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Partners: Faurecia Industries (FR), SiemensVDO Automotive AG (DE), MIRA Ltd (GB), Commissariat à lEnergie Atomique (FR), DaimlerChrysler AG (DE), Volkswagen AG (DE) Commission of the European Communities Directorate-General Information Society SAVE-U SENSORS AND SYSTEM ARCHITECTURE FOR VULNERABLE ROAD USERS PROTECTION Information Society Technologies: Systems and Services for the Citizen Project IST 2001 34040 Project funded by the European Community under the Information Society Technology Programme (1998-2002) Deliverable D6: Strategies in Terms of Vulnerable Road User Protection Authors: Co-Authors: Dr. Marc-Michael Meinecke Dr. Marian Andrzej Obojski, Dr. Dariu Gavrila, Mr. Erwan Marc, Mr. Richard Morris, Mr. Matthias Töns, Dr. Laurent Letellier Dissemination Level: PU Version: 3.0 Contract Date: Document Date: 01/03/2002 11/12/2003

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SAVE-U D6: Strategies in Terms of VRU Protection

Partners: Faurecia Industries (FR), SiemensVDO Automotive AG (DE),MIRA Ltd (GB), Commissariat à l�Energie Atomique (FR),

DaimlerChrysler AG (DE), Volkswagen AG (DE)

Commission of the European Communities � Directorate-General Information Society

SAVE-U

SENSORS AND SYSTEM ARCHITECTUREFOR VULNERABLE ROAD USERS PROTECTION

Information Society Technologies: Systems and Services for the Citizen

Project IST � 2001 � 34040Project funded by the European Community under

the �Information Society Technology� Programme (1998-2002)

Deliverable D6:Strategies in Terms of

Vulnerable Road User Protection

Authors:Co-Authors:

Dr. Marc-Michael MeineckeDr. Marian Andrzej Obojski, Dr. Dariu Gavrila,

Mr. Erwan Marc, Mr. Richard Morris,Mr. Matthias Töns, Dr. Laurent Letellier

Dissemination Level: PUVersion: 3.0

Contract Date:Document Date:

01/03/200211/12/2003

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Revision chart and history log

Version Date Reason1.0 11.09.2002 First draft version2.0 04.04.2003 Final Version presented during the

SAVE-U meeting in Grenoble3.0 11.12.2003 Revised version according to the

comments from the EuropeanCommission during Annual ProjectReview #2 (October 15, 2003)

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Contents

REVISION CHART AND HISTORY LOG .................................................................. 2

CONTENTS................................................................................................................ 3

CREDITS.................................................................................................................... 7

1. EXECUTIVE SUMMARY.................................................................................. 8

2. INTRODUCTION ............................................................................................ 10

3. IDENTIFICATION OF POSSIBLE ACTUATOR CONCEPTS FORVULNERABLE ROAD USER PROTECTION................................................ 11

3.1 Motivation..................................................................................................... 11

3.2 Classification of actuators for protection of vulnerable road users ....... 12

3.3 Definition of reversible and non-reversible protections methods........... 15

3.4 Four Phases for deployment of protection systems ................................ 17

3.5 Research of literature, patents and internet publications........................ 21

3.6 Description of different protection systems currently under investigation....................................................................................................................... 22

3.6.1 Automatic Braking ....................................................................................... 223.6.1.1 Components of a Braking System ........................................................ 233.6.1.2 Different Technologies of electronic controlled Braking Systems ......... 25

3.6.1.2.1 Electronic Controlled Brake Booster ............................................. 263.6.1.2.2 Electro-Hydraulic Brake (EHB)...................................................... 273.6.1.2.3 Electro-Mechanical Brake (EMB) .................................................. 30

3.6.1.3 Effect of different kinds of braking......................................................... 343.6.2 Airbags ........................................................................................................ 35

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3.6.2.1 Occupant Airbag ................................................................................... 363.6.2.1.1 Inflator ........................................................................................... 373.6.2.1.2 Bag................................................................................................ 383.6.2.1.3 Crash sensors............................................................................... 40

3.6.2.2 Exterior Airbag ...................................................................................... 423.6.2.3 Windshield airbag ................................................................................. 44

3.6.3 Hood lifting system ...................................................................................... 453.6.3.1 Hood lifting by bellows .......................................................................... 493.6.3.2 Hood lifting by pneumatic muscles ....................................................... 503.6.3.3 Sensor technology for deployment ....................................................... 523.6.3.4 Time flow of hood deployment .............................................................. 55

3.6.4 Active bumpers concepts ............................................................................ 583.6.4.1 Crash active and non crash active bumper systems............................. 603.6.4.2 Possible Concepts ................................................................................ 61

3.6.4.2.1 Pneumatic drive ............................................................................ 613.6.4.2.2 Hydraulic drive .............................................................................. 643.6.4.2.3 Electro hydraulic drive................................................................... 653.6.4.2.4 Mechatronical drive ....................................................................... 66

3.6.4.3 Summary and Prospects....................................................................... 673.6.5 Enhancement of driver's view...................................................................... 68

3.6.5.1 Technology of rain sensors for automatic windshield wiper control ...... 683.6.5.2 Rain Repellent Windshields .................................................................. 713.6.5.3 Headlights............................................................................................. 723.6.5.4 Active Night Vision ................................................................................ 73

3.6.6 Night vision.................................................................................................. 743.6.6.1 Physical basis ....................................................................................... 743.6.6.2 Current production application .............................................................. 753.6.6.3 Further development and prospects ..................................................... 77

3.6.7 Driver Warning ............................................................................................ 783.6.7.1 Warning signals .................................................................................... 793.6.7.2 Criteria of warning effects ..................................................................... 803.6.7.3 Categorisation of warning signal failure ................................................ 803.6.7.4 Recommendations................................................................................ 81

3.6.8 Pedestrian warning...................................................................................... 833.6.9 Electronic controlled Seat-Belt Pre-Tensioner............................................. 85

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3.7 Rules for road constructions to guarantee the visibility and safety ofVRU ............................................................................................................... 88

3.7.1 Problems and solutions ............................................................................... 883.7.2 Safety strategies in urban areas of Europe ................................................. 89

3.7.2.1 Installation of an accident scene management in Austria ..................... 903.7.2.2 Developing of Urban Management and Safety (DUMAS) ..................... 903.7.2.3 Efficiency of infrastructural measures for Pedestrian protection inFrance and the United Kingdom ........................................................................ 91

3.7.3 Examples..................................................................................................... 963.7.3.1 Tunnel and Subways ............................................................................ 963.7.3.2 Invisibility of VRU in case of parked cars .............................................. 993.7.3.3 Single-side illuminated road................................................................ 1003.7.3.4 School problematic ............................................................................. 101

4. IDENTIFICATION OF SYSTEM CONCEPTS FOR VRU PROTECTION ONVEHICLES................................................................................................... 103

4.1 Success of pedestrian protection in the EU in recent years.................. 103

4.2 Evaluation of actuators ............................................................................. 104

4.3 Deceleration ............................................................................................... 107

4.4 Driver Warning Strategies......................................................................... 111

4.5 Pedestrian Warning Approaches.............................................................. 111

4.6 Impact on sensor specifications and system specifications................. 1124.6.1 Sensor system specification versus application ........................................ 1124.6.2 Measurement accuracies � Maximum range............................................. 1134.6.3 Time scheme for deployment of warning signals or automatic decelerationactuators ............................................................................................................. 1224.6.4 Sensor specification .................................................................................. 125

4.6.4.1 Radar sensors .................................................................................... 1264.6.4.2 Video sensors ..................................................................................... 128

4.7 Sum up according analyzed actuators and sensors .............................. 132

5. CONCLUSION ............................................................................................. 135

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6. REFERENCES ............................................................................................. 137

7. LIST OF FIGURES....................................................................................... 143

8. LIST OF TABLES......................................................................................... 146

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Credits

This document was prepared by partners of the SAVE-U consortium. Please contactone of the following project partners for further information regarding this documentor the project.

Commissariat à l�Energie Atomique (CEA)/ France

DaimlerChrysler AG/ Germany

FAURECIA Industries/ France

MIRA Ltd./ United Kingdom

SiemensVDO/ Germany

VOLKSWAGEN AG/ Germany

Project Co-ordinator:

Name: Philippe MarchalCompany: Faurecia IndustriesPhone: +33-3 81 36 48 10Fax: +33-3 81 36 45 20E-mail: [email protected]

Workpackage Leader:

Name: Dr. Marc-Michael MeineckeCompany: Volkswagen AGPhone: +49-5361-9.20663Fax: +49-5361-9.57.20663E-mail: [email protected]

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1. Executive Summary

This document is one of the deliverables of the EC-Project �SAVE-U � Sensors andsystem Architecture for VulnerablE road Users protection�. It is the outcome ofWorkpackage WP3 entitled �Identification of system concepts for the protection ofVulnerable Road Users (VRU)�.

The objective of this document is to identify so-called active systems that are reallyuseful for protection of vulnerable road users (VRU) in case of critical trafficsituations between vehicles and VRUs.

The target set by the EU Commission was to reduce pedestrian fatalities by 30 %and severe injuries by 17 % by 2010.

This document provides an overview of what is currently under considerationregarding protection of vulnerable road users. There are many ideas, mainly comingfrom Europe, America and Asia, which are in a research stage. In this document asurvey about conference papers, patents and presentations on the internet is given.It is clear, this bibliography cannot summarise all approaches and all researchresults, but a high number of references from international sources are provided. Theabstract of each of these references is provided for better information for the reader.

A main part of this document is based on a �pure� technical description of actuatorsto understand physical details. The full breadth of actuators currently underdiscussion will be described from a technical perspective.

Starting from this technical description an evaluation of the actuators for VRUprotection systems will be derived. There are so-called passive, preventive andactive measures for VRU protection currently under consideration.

The actuators can be categorised into reversible and non-reversible (irreversible)protection measures. Current sensor systems for precrash applications or driverassistance system in general (e. g. cameras with image processing and radarsensors) have high performance, but the requirements in this field are much

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stronger. Consequently, the current sensors, which do not have a 100%-fault safestage, are only applicable for reversible protection systems.

Because of basic physical relationships passive measures can provide limitedprotection potential only. Therefore active and preventive actuators are helpful toenhance the protection effect for VRUs. For example, automatic vehicle decelerationin case of critical situations seems to be a potential approach for active VRUprotection (refer SAVE-U Deliverable D1 [SAV03]).

In addition to this warning strategies are of interest. But it is very important to providethe warning signal (acoustically, haptically or optically) early enough to the driver.Due to the typical reaction time of an average driver of about 1 second it is obviousthat the warning signal has to be provided to the driver more than 1 second beforethe contact vehicle with VRU. But 1 second before the potentially contact occurs it isnot 100% clear if the collision really will happen due to the unknown trajectories ofthe objects. Therefore, many false alarms seem to be inescapable. Consequently,driver warnings have to be investigated if they are really helpful or if they are onlydriver confusing.

The focus in this SAVE-U project will be on automatic deceleration and some studiesin terms of driver warning.

Detailed specification of the SAVE-U protection system that will be installed on twodemonstrator vehicles will be provided in the Deliverable D 22 as a result of WP 10�Building of prototypes and fitting on cars�.

Keywords: pedestrian, protection, actuators

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2. Introduction

This document is one of the deliverables of the EC-Project �SAVE-U � Sensors andsystem Architecture for VulnerablE road Users Protection�. It is the outcome ofWorkpackage WP3 entitled �Identification of system concepts for the protection ofUnprotected Road Users (VRU)�.

The objective of this document is to identify so-called active systems which are reallyuseful for protection of vulnerable road users (VRU) in case of critical trafficsituations between vehicles and VRUs.

This document provides first in chapter 3 an overview of what is currently underconsideration regarding protection of vulnerable road users. There are many differentsystems, mainly coming from Europe, America and Asia, which are underdevelopment or in a research stage. After a summary of a bibliography in this field itis really helpful to have �pure� technical information about actuators available tounderstand physical details. The full breadth of actuators currently under discussionwill be described from a technical perspective.

Most systems described in chapter 3 are currently in an early stage. Theeffectiveness for VRU protection of these systems can not be predicted todayexactly.

An evaluation of actuators is provided in chapter 4 in terms of efficiency for VRUprotection and in terms of impact on sensor specifications. Chapter 4 deals also withthe selection of system candidates for the SAVE-U project.

Finally, chapters 5, 6, 7 and 8 list the conclusions, references, figures and tables,respectively. The �Deliverable D6 Annex� contains the detailed bibliography on VRUprotection systems as a survey about conference papers, patents and presentationson the internet is given.

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3. Identification of possible Actuator Concepts for Vulnerable RoadUser Protection

3.1 Motivation

This chapter describes protection systems from a technical perspective that arecurrently under discussion, under development or in a research stage for futurevehicles. This description is important to understand and evaluate how they can beused for effective VRU protection. Especially, this is also helpful to be able to selectthese kinds of actuators which will be implemented into the SAVE-U demonstratorvehicles from DaimlerChrysler and Volkswagen at the end of the project.

The Figure 3.1 below illustrates a collision between vehicle and pedestrian. In thisfigure a collision with a child is depicted as a special variant case. It is obvious, thatthis situation is very dangerous for the pedestrian. The whole body of the pedestriancan be endangered, namely the legs, the torso, the thorax and the head.

Figure 3.1. Example of collision pedestrian versus vehicle.

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To avoid such kind of collisions or to reduce the impact of the contact differentprotection concepts are currently under research and/ or under development in theautomotive supply industry. An overview will be given about these concepts in thischapter.

First of all, a classification of these protection systems into four groups is introducedto clarify the differences between the different concepts. Second, the differentphases before the deployment of protection devices are explained. This partindicates particularly the conditions for deployment. The main section gives thetechnical description of actuators.

However, the list of protection systems that are identified is not only restricted toVRU protection devices. For example, the description of exterior airbags refers to thetechnology that is used in occupant airbags because exterior airbags will be actuatedin a similar way.

The other reason to describe pure occupant protection systems (like seat belt pre-tensioners) is that VRU and occupant protection cannot be considered totally isolatedfrom each other. As an example, if automatic deceleration is integrated into vehiclesin the next years then the installation of pre-tensioners could be necessary as well inorder to prepare the driver to the modification of vehicle behaviour.

Finally, in order to get a complete overview of the solutions for improving VRUsafety, important hints will be given too about the possibilities of enhancement ofroad infrastructure in addition to protection systems installed on vehicles.

3.2 Classification of actuators for protection of vulnerable road users

In the field of protection systems for vulnerable road users three different approachesare under discussion (see Figure 3.2). These terms are well known in the technicalcommunity of the European Commission.

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First, passive protection systems are possible. These systems are useful to reducethe accident severity if a crash really occurs. Passive systems can be divided intotwo sub-classes: pure-passive and crash-active methods. In details:

The class of pure-passive systems contains typically measures in thedomain of vehicle design layout.

A special variant of the passive protection systems are the so-called crash-active protection systems. These systems are passive in general. But onlyin the case if a crash occurs or if the crash is unavoidable then thoseactuators will be activated and the effect of protection increases.Consequently, the crash-active protection systems have the goal to reducethe accident severity with active components using countermeasures.

Second, active protection systems are possible. Critical traffic situations will bereduced in their criticality by using active components. For example, parameters ofthe brake system can be adjusted in case of critical situations.

The third category is entitled preventive protection methods. The intention is toavoid crashes or reduce severity of accidents in an early stage. Therefore, typicallythis method needs foresighted sensors.

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Systems for Protectionof unprotected road users

Systems for Protectionof unprotected road users

Preventive MethodsPassive Methods

Crash-ActiveMethodsPure Passive

Methods

Systems for Protectionof unprotected road users

Active Methods

reversible irreversible reversible irreversible reversible irreversible

reversible irreversible

Figure 3.2. Overview about passive and active methods for protection ofunprotected road users.

This document is focused on crash-active protection systems and preventivesystems. Pure passive protection systems are well known in the automotivecommunity from the literature. They will not be described in detail in this report.Active systems will be described briefly as well.

Some examples for pure-passive/ crash-active and active methods are given in thefollowing.

Examples of pure-passive methods are:- Soft front structures- Enhancement of driver�s view

Examples of crash-active methods are:- Lifting hood- Exterior airbags (e. g. Windshield Airbag)

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Examples of active methods are:- Brake-Assistant- Electronic Stability Program (ESP)

Examples of preventive methods are:- Driver warning- Automatic comfort braking- Pedestrian warning- Support of automatic emergency braking

The following protection systems are under discussion/ under development for futurevehicles. However, it is very important to evaluate the use of these systems forprotection of vulnerable road users. This will be done in the chapter after. In additionto this important hints will be given regarding to possibilities of enhancements ofinfrastructure.

In this deliverable not only VRU protection systems will be described. Also someoccupant protection systems are described, if this general technology is importantand similar for future VRU protection systems (e. g. occupant airbag � exteriorairbag).

In addition to the VRU protection system description pure occupant protectionsystems (like seat belt pre-tensioners) are described. The reason for this is, thatVRU protection and occupant protection cannot be considered totally isolated fromeach other. The serious view in the future is, that in the case if VRU protectionsystems (like automatic deceleration) will be integrated into vehicles in the next yearsthe installation of pre-tensioners could be necessary.

3.3 Definition of reversible and non-reversible protections methods

The actuators described in the paragraph before can also be differentiated by theirkind of deployment. There are reversible and non-reversible systems currently underdiscussion:

Reversible deployment:

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A trigger signal activates the actuator. A second signal can deactivate theactuator in that way, that the actuator has the same state as before the firstdeployment.

Non-reversible deployment:It is also the case, that the actuator will be activated by a trigger signal. Thedifference to reversible methods is that there is no possibility to deactivate theactuator. Therefore, irreversible methods can be deployed one time only. Afterthat, deployment components have to be changed in the garage.

The following table shows examples of reversible and non-reversible protectionsystems.

Reversible Systems Non-Reversible Systems Driver Warning Seat-Belt Pre-Tensioner

(electronically deployment) Automatic Comfort Braking Pedestrian Warning

Exterior Airbags Seat-Belt Pre-Tensioner

(pyrotechnically deployment) Active Bumpers

Hood Lifting(reversible version)

Emergency Braking(reversible version)

Hood Lifting(non-reversible version)

Emergency Braking(non-reversible version)

Table 3.1. Examples of reversible and non-reversible protection systems.

Some systems can be assigned to these two categories very easily. However, inTable 3.1 two examples are written, who can not be so easily classified, namelylifting hood and emergency braking. There are different technologies currently in thediscussion. Therefore, the classification of these actuators depends mainly on theconcrete realisation.

The main advantages and main disadvantages of reversible and non-reversiblesystems are summarised in Table 3.2.

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Reversible Systems Non-Reversible Systems No 100%-fault-safe sensors

required Eventually dosed trigger possible Activating (deployment)

and Deactivating(e. g. in case of a false alarm)of actuator possible

100%-fault-safe sensors required 100%-fault-safe sensor fusion

algorithm and scene interpretationrequired

High Risks:No focus on non-reversibleprotection systems in the SAVE-Uproject

Table 3.2. Consequences of reversible and non-reversible methods.

Due to the fact, that the SAVE-U sensor platform will consist of non-100%-fault safesensors, it is not realistic to deploy non-reversible actuators. The two SAVE-Udemonstrator vehicles will base on reversible methods, exclusively (see chapter 4).

3.4 Four Phases for deployment of protection systems

Different methods for protection systems were presented in the previous sections.Each of them needs its special individual deployment strategy. This section dealswith the general description for triggering a special protection system.

The deployment strategy of protection systems can be divided into the followingphases. Each phase is described in words and also is illustrated by a pictogram foreasier understanding:

Phase 0. Phase 0 is not really a phase for deployment, it is the time before. Thisis introduced for better understanding only. Before phase 1 (acquisitionphase) the VRU is invisible, as depicted in the following graph. There isno chance to detect the VRU with the sensor system in this area. Ofcourse, during this period the automatic deployment cannot doanything.

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Figure 3.3. Deployment of actuators: Phase 0 (VRU invisible)

Phase 1. The first phase can be identified as the acquisition phase. The objectmoves into the detection area/ operation area of a sensor or sensorsystem.For example, an object can be observed from a radar sensor atdistances less than radar maximum range (e. g. 25 m). The theoreticalradar maximum range is given by internal radar parameters like pulserepetition frequency, signal-to-noise-ratio and others.After an object had entered the detection area the sensor/ sensorsystem needs a special period for detecting. This period is calledacquisition time nAcquisitiot .

In case of radar the acquisition time depends on parameters likemeasurement time (update rate), signal stability, tracking strategies andothers. A rough rule for automotive radars is: Acquisition time is 8xmeasurement time. So, if a radar sensor needs 20 ms for ameasurement, the acquisition time is in the order of 160 ms.

Figure 3.4. Deployment of actuators: Phase 1 (acquisition phase)

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Phase 2. The second phase can be identified as tracking phase. During thisperiod Trackingt several measurements are collected, position data are

tracked over time and the trajectory will be estimated. To get therequired stability of the trajectory many measurements are necessary toincrease the measurement accuracy of a single measurement.

Figure 3.5. Deployment of actuators: Phase 2 (tracking phase)

Phase 3. Following the first two phases the deployment phase is located on thetime axis. The deployment of a protection system is based on theestimated trajectory of phase II. A protection will be deployed if:a) Trajectory (x-, y-position over time) of the VRU and the trajectory of

the host vehicle will have an intersection,b) the calculated time-to-collision (TTC) is equal to the required

deployment time ActuatorDeploymentt , of the specific actuator (e. g.

deployment time of a windshield airbag). The goal is to have tomaximum degree of protection available at the contact betweenobject and host vehicle,

c) Considering all the degrees of freedom of the object, of the hostvehicle (taking in account measurement accuracies of the sensorsystem), two cases are possible:

Case A (Non-reversible deployment):Test if the predicted collision is unavoidable. Deployment willbe done only in case of so-called unavoidable collisionsituations.

Case B (Reversible deployment):Test if the predicted collision has a high probability.

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SAVE-U will not deal with actuators like inflatable hood, windshieldairbags and so on, because this project is mainly sensor-orientedand not actuator-oriented. The actuator system, which will beintegrated on the two SAVE-U demonstrators, will realize thereversible deployment strategy (case B), because there are no100%-fault safe sensors currently on the market for a powerful non-reversible deployment.

Figure 3.6. Deployment of actuators: Phase 3 (deployment phase)

Phase 4. After the deployment phase the contact between object and hostvehicle occurs. At this moment, the protection system must offer thehighest level of protection effect, which is possible. Consequently, thecomplete sensor system must be well adjusted and parameterised toprovide this high protection effect to the collision object.

Figure 3.7. Deployment of actuators: Phase 4 (contact)

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In this description the four phases for deployment were introduced. The timing anddistance values (e. g. nAcquisitiot , Trackingt , ActuatorDeploymentt , ) are calculated in chapter 4 for

different vehicle velocities. Results can be found in Figure 4.10.

3.5 Research of literature, patents and internet publications

In the D6 Annex a large literature overview is presented. It consists of three mainsurveys: on published papers, on published patents and on web-pages on theinternet.

The orientation of the survey was to find an optimal contribution for choose suitablemethod and technology for most important components of SAVE-U system. Thisorientation was found as result of the theoretical analysis for sensor expectedcapabilities and actuator needed parameters (see chapter 3 and 4).

The survey is made as a composition of short summaries of found descriptions. Theadvantages and disadvantages of proposed solutions for Active Hood, AutomaticBraking, Driver Warning, Night Vision, and Advanced Front Lighting etc. arepresented.

Starting with the overview of technical solutions for active, passive and preventivepedestrian protection systems a description, how such systems work and how theirfeasibility for this tasks is was done.

In the second section of that chapter the research for recognize strategies fordeployment of protection systems is made.

The last scope of the literature research is focused on the description of sensors,accident statistics and regularities for VRU protection.

The same structure features the research on published patents. The analysis ofpatent - publications was made from the same point of view as the analysis ofpublications.

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In the parts of researches of internet publication the publications of relating solutionsoffered by car producers and deliverers of technical solutions for car manufacturerswas stressed.

3.6 Description of different protection systems currently underinvestigation

This paragraph will list potential protection systems able to improve VRU safety. Itwill describe especially the following systems:

Automatic braking Occupant airbag Exterior airbag Windshield airbag Active bumpers concepts Hood lifting system Enhancement of driver's view Night vision Driver warning Pedestrian warning Seat-belt pre-tensioner

In addition to vehicle-based actuator concepts hints for selected road constructionsitems (construction of road infrastructure) will be given.

3.6.1 Automatic Braking

In this paragraph technical aspects about electronic controlled braking will be given.

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Figure 3.8. Example of a conventional braking system.

3.6.1.1 Components of a Braking System

The braking system is the totality of brake environment inside of a vehicle, which isuseful to reduce the velocity, to reduce the acceleration, or to bring a vehicle to stop,or hold the vehicle in a standing position.

The braking system consists of the following elements: Energy supply environment:

The energy supply environment consists of components, which provide theenergy, which is necessary for braking, control of the brake, and eventually forto prepare energy for braking.The source for this energy is normally located inside the vehicle, but there isan other possibility, namely to have the energy source located inside of thetrailer. The source for brake energy can be the power of muscular strength ofthe vehicle driver or compressed air or others.

Brake activation environment:The brake activation environment includes components of a vehicle brake,which initiate the action of a braking system and control the braking system inthis way. This control signal can be transmitted by using mechanical,electrical, or pneumatic or hydraulic connections. It is possible to useadditional external energy supply to do that.

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The brake activation environment starts with that component of the brakingsystem on which the control force acts on. The activation of the brake can bedone for example:a) Directly by foot or handb) By indirect activation by the vehicle driverc) By change of the brake pressure or the electrical current in the

connection between vehicle and trailer in case of activating the brake orin case of failure in the braking system

d) By mass inertia or weight of the vehicleThe end of the brake environment is defined at that point, where the energyfor braking will be distributed among other brake components.

Figure 3.9. Example of a brake booster.

Transmission environment:The transmission environment includes components of the braking system,which transports the energy for braking from the brake activation environmentto the brake itself. The interfaces are well clear specified. The start point is theactivation environment ends and the energy supply environment ends. Theend point is specified at these components where the brake forces aregenerated.The transmission environment can base on e. g. mechanical, hydraulic-pneumatic (overpressure or negative pressure) and electrical concepts orcombination of these concepts (e. g. hydro-mechanical or hydro-pneumatic).

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Brake:The brake itself is defined as those components, which are able to generatethe forces to reduce the movement (velocity) or movement tendency.Examples for brakes are:a) friction brake (based on disks or drums)b) retarder/ decelerator (hydro-dynamical retarder or engine brake)

Figure 3.10. Components of a brake system.

Additional environment inside of a tractor vehicle necessary for vehicle trailer(for tractor vehicles only):This additional environment is necessary to supply the brake of the trailer withenergy and control signals. This environment consists of components of theenergy supply environment of the tractor vehicle and the coupling head of thesupply line (inclusive) and parts of the transmission environment between thetractor vehicle and the coupling head of the brake line (inclusive).

3.6.1.2 Different Technologies of electronic controlled Braking Systems

The general tendency of automotive research/ development is to have all functions ofvehicle dynamic under electronic control. So-called brake-by-wire, steer-by-wire oraccelerate-by-wire is well known in the scientific automotive world. A vehicle, whichincludes all these electronically controlled functions, is called X-by-wire vehicle.

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Currently different technologies of electronic controlled braking systems are underdiscussion. In the following, the main topics of those technologies will be described.

For VRU protection the electronic control capability of a braking system is veryimportant. There is no request of one specific braking system technology from a VRUprotection point of view.

3.6.1.2.1 Electronic Controlled Brake Booster

There are two basic types of brake booster: vacuum assistant and hydraulicallyassistant. Currently these systems are mainly in a research stage in the automotivemanufacturer industry.

Only a few years ago, this sort of system could not have existed - merely because ofthe rudimentary microprocessors available then.

Neither their storage capacity nor their working speed would have been sufficient tocope with the huge amounts of data and extremely short CPU times. But that's nolonger a problem thanks to the invention of digital signal processors, there is a realpossibility that the autonomous intelligent cruise control unit will go into seriesproduction.

These kinds of processors, which have not previously been used in cars, arecharacterised by a particularly high working speed and can evaluate data in splitseconds.

The engineers are also venturing into new technical territory with automatic brakecontrol. They have developed an electronically controlled brake booster with asolenoid valve that even responds to very gentle braking commands. It is all thanksto this innovation that automatic proximity control has been made possible: throughaccurately metered brake applications - which are hardly noticed by the driver - theexperts can keep the test car constantly at the correct distance and it can also reactvery quickly to new traffic situations should they arise.

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3.6.1.2.2 Electro-Hydraulic Brake (EHB)

Electro-hydraulic braking (EHB) systems are designed to allow electronic control ofvehicle braking while retaining a reduced hydraulic system. The hydraulic system isable to function as a back up in the event of a failure in the electronic control.

The EHB control unit receives inputs from sensors connected to the brake pedal. Innormal operation, a backup valve is closed and the controller activates the brakes ofthe wheel through an electric motor driven hydraulic pump. It is only if the controllergoes into a fail safe mode that the backup valve is opened allowing the brakes to becontrolled via a conventional hydraulic circuit.

With EHB we are advancing the technical potential of hydraulic brake systems: thehydraulic link between the brake pedal and the wheel brake is replaced by a by-wire-transmission which offers considerable advantages.

Figure 3.11. Electro-hydraulically Brake (EHB).

Compared to the operation of conventional braking systems, by depressing the brakepedal with the Electro-Hydraulic Brake System (EHB) the appropriate command istransmitted electronically to the electronic controller of the hydraulic unit. Thisdetermines the optimum braking pressure and actuates the brake callipershydraulically.

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Hydraulicunit

EHB brake system

Brake operating Signal interface(Gateway)

Braking function

Intelligent interface

Pedalsimulator

front wheels

Wheel modulatin valves

Car steering systems

Sepa-ratingvalves

Hydraulicenergysupplaysystem

rear wheels

highpresureaccumu-

lator

CAN

CAN

- brake booster- brake shifting- ABS, ASR, VDC- ECU

Hydraulicunit

EHB brake system

Brake operating Signal interface(Gateway)

Braking function

Intelligent interface

Pedalsimulator

front wheels

Wheel modulatin valves

Car steering systems

Sepa-ratingvalves

Hydraulicenergysupplaysystem

rear wheels

highpresureaccumu-

lator

CAN

CAN

- brake booster- brake shifting- ABS, ASR, VDC- ECU

Figure 3.12. Block diagram of an electro-hydraulic braking system [BOS02].

Components of the EHB: Electronic control unit Electronic pedal module with pedal feel simulator and sensors for monitoring

driver settings

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Figure 3.13. Comparison between a conventional brake system and an electro-hydraulic brake system (EHB).

The potential advantages of the EHB system include mainly comfort braking andpackaging, but there are some others:

Simplified calibration process as brake response and pedal feel can beadjusted in software

Improved connectability with other emerging systems like Adaptive CruiseControl.

Flexible installation due to the absence of the large vacuum servo.

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The Anti-lock Braking System (ABS) can be active without feedback from thepedal.

Optimized braking and stability behaviour Optimized pedal feel No pedal vibration during ABS mode Improved crash worthiness Improved packaging, less installation effort A high level of technology re-use for hydraulic system suppliers, while

incrementally building on development of advanced electronic systems likeanti-blocking system (ABS), electronic stability program (ESP), BrakeAssistant, adaptive cruise control (ACC) etc.

3.6.1.2.3 Electro-Mechanical Brake (EMB)

Electro-Mechanical Braking Systems (EMB), also referred to by some as Brake byWire, takes the place of conventional hydraulic braking systems with a completely'dry' electrical component system by replacing conventional actuators with electricmotor driven units. This move to electronic control helps to eliminate many of themanufacturing, maintenance, and environmental concerns associated with hydraulicsystems.

This new technology is also currently in a research stage. No serial products areavailable on the market at this moment. This braking system can only operate in42 V vehicle network.

Because there is no mechanical or hydraulic back-up system, reliability is critical andthe system must be fault tolerant. The implementation of EMB, therefore, requiresfeatures such as a dependable power supply fault tolerant communications protocols(i.e., TTCAN and FlexRay) and some level of hardware redundancy.

As in Electro-Hydraulic Braking (EHB), EMB is designed to improve connectivity withother vehicle systems, thus enabling simpler integration of higher level functionssuch as traction control and vehicle stability control. This integration may vary fromembedding the function within the EMB system, as in ABS, to interfacing to theseadditional systems using communication links.

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Another advantage of both EHB and EMB systems is the elimination of the largevacuum booster found in conventional systems. Along with reducing the dilemma ofworking with increasingly tight space in the engine bay, this elimination helps simplifyproduction of right and left-hand drive vehicle variants. An increase in flexibility forthe placement of components is also provided by EMB systems over those of EHBwith the total elimination of the hydraulic system.

EMB systems represent a complete change in requirements from previous hydraulicand Electro-Hydraulic Braking systems. The EMB processing components must benetworked using high reliability bus protocols ensuring comprehensive fault toleranceas a major aspect of system design.

The use of electric brake actuators means additional requirements including motorcontrol operation within a 42 V power system as well as high temperature and highdensity to the electronic components.

In addition to supporting existing communications standards such as CAN and K-line,EMB systems require the implementation of deterministic time-triggeredcommunications like those available with FlexRay� to assist in providing therequired system fault tolerance. The EMB nodes may not need to be individually faulttolerant but help to provide failsafe operation and rely on a high level of faultdetection by the electronic components.

These new system requirements must be met using high-end components at verycompetitive prices in order to replace established, cost effective technology, whilemaintaining strict adherence to the automotive qualification.

Delivering the large current requirements to stop a large SUV may cause limitedadoption at first. The first implementation will be on small car platforms.

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Figure 3.14. Electro-mechanical brake (EMB).

With the EMB we are getting involved in pure brake-by-wire technology, whichdispenses with brake fluids and hydraulic lines entirely. The braking force isgenerated directly at each wheel by high performance electric motors, they arecontrolled by an ECU and actuated by signals from an electronic pedal module. TheEMB includes all brake and stability functions such as ABS, EBD, TCS, ESP, BA andACC. It is virtually noiseless, even in ABS mode.

Components of the EMB Four wheel brake modules Electronic controller Electronic pedal module with pedal feel simulator and sensors for monitoring

driver settings

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Figure 3.15. Comparison between conventional brake system and electro-mechanical brake system (EMB).

The potential benefits of the EMB systems include: A reduction in system weight resulting in improved vehicle performance and

economy Simpler and faster assembly of the system into the host vehicle Pollutant source reduction through elimination of corrosive and toxic hydraulic

fluids

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Increased flexibility of placement due to removal of vacuum servo andhydraulic system

Reduced maintenance requirements Implementation of features such as 'hill hold' Freedom of design due to removal of mechanical components Shorter stopping distances and optimized stability More comfort and safety due to adjustable pedals No pedal vibration in ABS mode Virtually silent Environmentally friendly no brake fluid Improved crash worthiness Space saving, using less parts Simple assembly Capable of realizing all required braking and stability functions such as ABS,

ESP, BA, ACC etc. Can be easily networked with future traffic management systems. Additional functions such as an electric parking brake can be integrated easily.

3.6.1.3 Effect of different kinds of braking

In Figure 3.16 different types of braking are shown. The standard car driver brakingbehaviour will be compared with experienced drivers and braking with brake-assistant. It is directly to recognize that the normal driver needs support in brakingsituations.

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Start of braking,v0 = 50 km/h

Impact withpedestrian

Standard driver

Experienced driver

Brake-Assistant

vK= 40 km/h

vK= 25 km/h

vK= 35 km/h

Decelerations with different brake-systems

0

2

4

6

8

10

12

0 0,2 0,4 0,6 1Time [s]

Brake-AssistantExperienced driverStandard driver

Figure 3.16. Simulated effects of different kind of braking.

3.6.2 Airbags

Airbags are restraints systems. They participate to passive safety (crash-activesystems), that is to say their functions are to limit crash consequences. Airbags areautomatic crash protection systems. At the moment their purpose is to restrainautomobile driver and passengers during a crash. This reliable technology installedin automobiles in the late 1980's is now expected to be used also for exterior airbagsfor pedestrian protection.

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Inside airbags and exterior airbags are different in many parameters. For example,pressure conditions and environment conditions for the bag (e. g. weather) are totallydifferent. Therefore exterior airbags require special technologies.

In this section three different kind of airbags will be described, namely occupantairbags, exterior airbags and windshield airbags. The following paragraph 3.6.2.1 willgive first some information about the different components in an occupant airbagsystem, as the firing system is expected to be the same for exterior airbag.'

3.6.2.1 Occupant Airbag

It is obvious, that occupant airbags are not VRU protection systems. Nevertheless,there is one reason because this is described in this document. Namely, occupantairbags are serial products for many years, the technology is well known, manyresearch activities were done in this field and therefore the technology of occupantairbags can be a good base to understand exterior airbags for VRU protection.

Inside airbags and exterior airbags are different in many parameters. For example,pressure conditions and environment conditions for the bag (e. g. weather) are totallydifferent. Therefore exterior airbags require special technologies.

Airbags are restraints systems. They participate to passive safety, that is to say theirfunctions are to limit crash consequences for the automotive occupants. Airbags areautomatic crash protection systems; their purpose is to restrain automobile driverand passengers during a crash, so the inflation has to be quick. More precisely,airbags are designed to keep the occupant's head, neck and chest from hitting thesteering wheel, the dashboard or the interior packaging. Also, airbags met outaccelerations to the occupant and minimize the stress on the occupant by distributingthe restraint forces over as much as possible area.

The airbags concept appeared in the early' 1970s, but it's only in the late 1980s thatthey were installed in automobiles.

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Figure 3.17. Airbag deployment.

Basically, airbag systems consist of 3 main components: an air bag module, crashsensor(s) and a diagnostic unit.

The air bag module is composed of an inflator, an initiator and an air bag itself.These components will be described in detail in the following sections.

3.6.2.1.1 Inflator

Because of its function, the airbag has to be filled quickly. The first idea for earlyairbag developers was to use high-pressure air stored in a tank and to release it witha quick action valve. An other solution is to use a solid propellant which combustionproduces inflation gas. Sodium aside was the main ingredient of gas generator,because of its chemical reaction characteristics which are suitable for inflating airbags (quantity of gas generated), and the primary combustion product is harmlessnitrogen gas. A mixed solution is hybrid inflators, which use a combination ofcompressed gas and solid fuel.

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Figure 3.18. Passenger airbag with hybrid inflator(http://www.autoliv.com/appl_alv/Autoliv.nsf/pages/library_illustrations)

Figure 3.19. Airbag inflation device with solid propellant(http://www.howstuffworks.com/airbag1.htm)

3.6.2.1.2 Bag

One of the first bag or cushion was in neoprene-coated nylon. The idea was toreduce the porosity of the bag, but in fact it was observed that the bag reacted like aspring, that is to say return to the occupant the energy stored during the first contact.The consequence was a rebound of the occupant into the seat back and head

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restraint. As a consequence, technical solutions were found to increase thedissipation of energy: porosity of the bag and vents. Vent holes are placed on theunderside to assure the correct soft landing, away from the occupants and othersources of blockage. The bag is also folded into the steering wheel, the dashboard,the seat or the door. The folding is precise to make it unfold fast and safely.

Figure 3.20. Airbag Vents.

Delphi tries to use a variable vent to modulate the protection. In fact, the idea is todivert a part of the gas used to inflate the bag, into the cockpit of the vehicle. Thestate of the vent will be controlled by a pyrotechnic device.

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Figure 3.21. Piloted vents (Delphi)

3.6.2.1.3 Crash sensors

The sensing time is the duration between the crash (or the contact) and the order ofdeployment. To detect the crash and to determine if the airbags have to be inflatedor not, crash sensors are used. Crash sensors were at the beginning electro-mechanical device. The general principle is a mass retained in a rest position by amagnet and, when the acceleration is strong, the mass can break free of the magnetand move to realize an electrical contact. Designers tried to place a sensor in thebumper, but it wasn't a safe location. Those sensors have to be reliable, to generatean inflation when crash severity is high. Two kind of dysfunction could appear:inadvertent deployment or failed deployment. To decrease inadvertent deployment, agroup of sensors "secondary or saving" is used. They're wired in series with aprimary or discriminating group of sensors. The saving group is defined to trigger atlower crash severity than the discriminating group in order to prevent failures todeploy.

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+ -

airbag

Discriminatingsensor

Safingsensor

To Trigg at lower crashseverities

Figure 3.22. Configuration of discriminating and saving sensors (adapted fromStruble)

Figure 3.23. Crash sensor (http://www.lemurzone.com/airbag/crash.htm)

Nowadays, sensors electro-mechanical described above, have not disappeared, theyare always used to limit inadvertent deployment. But, main sensors areaccelerometers placed on an electronic control unit; they provide continuous

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information concerning acceleration and deceleration of the vehicle. Softwarecompares this information to crash data stored in a memory. Crash data are definedduring various crash tests of the vehicle.

3.6.2.2 Exterior Airbag

Airbags are restraints systems. They participate to passive safety, that is to say theirfunctions are to limit crash consequences. Airbags are crash-active protectionsystems. At the moment their purpose is to restrain automobile driver andpassengers during a crash. This paragraph will give first some information about thedifferent components in an occupant airbag system, as the firing system.

When a collision is unavoidable, the exterior airbag has to build an air cushionbetween the colliding object and the vehicle. To form an airbag system there has tobe the three major components detection subsystem, control, deploymentsubsystem, and airbag subsystem.

Figure 3.24 shows the configuration scheme of an exterior airbag system.

Figure 3.24. Configuration of proactive exterior airbag systems

All major components have to be adapted to specific needs and must interact withthe others. This feature can be supported by data exchange systems or vehicle bussystems as CAN or LIN.

The external airbag�s stiffness must be adapted to the car stiffness and the bumperstiffness. Otherwise, it would not absorb a proper amount of crash energy.

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In comparison to internal airbags, all used material has to consider hard conditionslike extreme temperatures, moisture and mechanical stress by particles hitting theairbag�s peripherals.

Inside airbags and exterior airbags are totally different in terms of pressureconditions. In addition to this bags for outside and inside use are totally different interms of environment conditions like weather and others. Therefore exterior airbagsrequire special technologies.

It is not yet quite clear which kind of airbag is the best for use as an exterior one.There are two alternatives. The exhausted system, like it is used in interior airbagsystems, and the closed system.

Figure 3.25. Closed end exhausted airbag system

The exhausted system will reach energy dissipation by creating a high speed air flowthrough a series of valves. The advantage of this system lies in the temporarily builtcushion (see Figure 3.25).

The detection system has to work proactive and its reliability is essential for thewhole airbag system. To achieve an optimal detection result and to disable specific

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weaknesses as well as to achieve a proper redundancy level the system should useactive sensors which emit and receive energy like radar and passive vision basedsensors like cameras at the same time. Active sensors enable to detect relativespeed and distance to a preceding object in a single step. What these sensorscannot do, is to identify an object. For this purpose passive sensors are neededwhich in contrast to active sensors tend to have difficulties with poor weatherconditions. Consequently, from a technical point of view today it is not possible todeploy airbags using these sensors.

3.6.2.3 Windshield airbag

In many accidents pedestrian�s serious injuries do not result from the collision withthe car�s front end, but from the impact on the windshield area.

In comparison to metal parts of the car, the windshield gives way when an objectcollides with it. As a result, most serious injuries do not result from the contact withthe windshield but on the a-pillar or the windshield frame.

Taking this in account it�s thought about an exterior airbag that covers the entirewindshield frame (see Figure 3.26).

Figure 3.26. Windshield airbag

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In addition to the chapter 3.6.2.2 �exterior airbag� it must be thought about the placethe windshield airbag could be installed.

One possibility could be to install several airbags at or in the windshield�s frame. Thiswould have the advantage of small quickly inflated airbags. On the other hand thiswould lead to a broader frame and could result in deteriorated driver�s view. For thissubject see chapter 3.6.5 �enhancement of driver�s view�.

Another possibility could be the storage of a single airbag either in a bay between thehood and the windshield or under the rear part of the hood. The first suggestionwould result in a shortened hatch and so restrict access to the engine. The secondone should be a more consequent way.

Unfortunately this system has a high risk in case of false alarms for the driver,because the windshield airbag reduces the view of the driver dramatically. To solvethis problem a 100% fault safe sensors would be required. Such sensors are notavailable today.

It has to be mentioned that this solution is linked with great construction effort, but incombination with bumper airbag and the hood lifting system it could be a reasonablepedestrian security package. Especially the hood lifting would enable to store theairbag under the hatch without additional constructive effort.

For further information about exterior airbag systems see chapter 3.6.2.2 �exteriorairbag�.

3.6.3 Hood lifting system

A special protection system has been developed to decrease the severity of head-to-bonnet impacts. The system is activated at the impact by a sensor located in thebumper, at speeds above 20 km/h. The sensor is able to discriminate objects with adifferent geometry (another car versus a leg), as well as with a different stiffness (apole versus a leg). Two actuators lift the rear part of the bonnet approximately100 mm. The actuators were tuned to have lifted the bonnet at 60 � 70 milliseconds

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after the leg-to-bumper impact, but before the head impact. The actuators/ liftingelements were also tuned to stay up during the upper torso impact, but still beenergy absorbing to keep the head loading down if the head impact is on top of thelifting elements.

It is obvious, that only the reversible variant can be of interest due to false alarms bythe current sensors.

Modern cars have very stiff parts underneath the bonnet with gaps even less than20 mm. Therefore, the deformation distance is too small to allow for the necessaryenergy absorption.

Figure 3.27. Intrusion measurement on an adult dummy head.

The hood lifting system is a possibility to increase the space between engine andhood, if this is necessary because of the package.

To quantify the load on the head the HIC (Head Injury Criterion) value wasintroduced. HIC is an internationally accepted, acceleration-based measurement forthe violence against the head in a crash. HIC-values under 1000 imply that the riskfor life-threatening head injuries is 15 percent or less. But the curve rises sharply; at2000 HIC the risk is almost 90 percent.

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The HIC values depend not only on the deflection but also on many other factors,e. g. contour, inertia, stiffness and stability. Assuming the space between hood andengine is large enough (in case of deflected hood or not deflected hood) anundershooting of the requested HIC of 1000 can not be guaranteed today. Ratherdue to a lot of vehicle technical requirements �hard� parts on the hood (e. g. hinges,locks) are inescapably. At these hard locations the HIC of 1000 can not be achieved.Additional needs coming from requirements like resistance against hailstorm anddenting increase the difficulties.

The very important tests from Gläser and Zellmer (see Figure 3.28) were done inideal conditions with enough free space. They don�t take into account the vehicletechnical boundary conditions like hinges and locks.

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Figure 3.28. Bonnet head form tests performed at BASt in Germany, 40 km/himpact speed (Zellmer and Glaser, 1994)

The pedestrian protection system consists of two parts. The first part of theprotection system comprises two actuators for the lifting of the rear part of the bonnet(refer section 3.6.3.1 and section 3.6.3.2). This creates a distance between thebonnet and the stiff parts underneath the bonnet.

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3.6.3.1 Hood lifting by bellows

The protection system, an active bonnet, comprises two lifting elements, which liftsthe rear corners of the bonnet (refer Figure 3.29). The lifting elements consist ofcompressed metal bellows, which are filled with gas from micro gas generators at theevent of an impact. The benefits with the design are several.

1. The design does not need any sealing to keep the gas from leaking. The onlyopening in the bellow is where the gas generator is attached. Therefore, it iseasy to keep the pressure up a long time in the bellow. This is important sincethere can be large variations for when the head impacts occur, depending onthe size of the person and the impact speed.

2. The bellow is insensitive to the angle of the impact. (Some lifting devices canabsorb energy only if they get the impact at a perfect angle.)

3. The dimensions of the actuator can be made small. The height of the devicecan be less than the lifting distance, which is not possible for a lifting devicebased on a piston.

Figure 3.29. Bonnet with protection system in activated (lifted) position.

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3.6.3.2 Hood lifting by pneumatic muscles

An active hood can also be lifted up with a pneumatic muscle. An example isdepicted in Figure 3.30. This device can be contracted by the influence ofcompressed air. The pneumatic muscle is composed of a membrane of contractionand adapted ends of connection.

The membrane of contraction consists of a rubber pipe tight with the air underpressure, surrounded by an extremely resistant fibre sleeving. These fibres form agrid in rhombus presenting the form of a three-dimensional latticed structure.

When an internal pressure is applied, the pipe dilates in the radial direction,generating a force of traction, as well as a movement of contraction of the muscle inthe axial direction. The force of traction is with its maximum at the beginning of thecontraction and decrease in a quasi linear way up to zero during the race. Thepneumatic muscle makes it possible to carry out races being able to go up to 25 %nominal length of the muscle (see Figure 3.31). The pneumatic muscle is an actuatorwhich works exclusively in traction. It cannot transmit efforts of pressure and doesnot have guidance. Dilation in the radial direction cannot be used for operations oftightening, because the movement of contraction can generate frictions which woulddamage the muscle.

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Figure 3.30. Example of a pneumatic muscle.

contraction [%]25%

2000

Power[N]

Figure 3.31. Contraction of a pneumatic muscle for hood lifting.

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To do a derivation for a sensor system, it is necessary to know the reaction time ofan active system. The following table depicts the reaction time measurement ofsome pneumatic muscles. In the test measurement, two pneumatic muscles lifted thehood. They lifted the hood to 80 mm and 90 mm on the mounting area (near thewindscreen).

muscle compressedair

liftinghigh

musclereaction

timeA 8 bar 80mm 45msB 8 bar 80mm 35msB 12 bar 80mm 32msB 8 bar 90mm 38ms

Table 3.3. Reaction time (measurement results).

3.6.3.3 Sensor technology for deployment

The task of the sensor is not only to sense the impact very fast, but also to detectwhether the impacting object is a person or some other object. The sensor systemconsists of two different components. A �membrane switch�-type contact sensorcovers the complete width of the bumper. It is placed in the foam just inside theplastic cover of the bumper. Two accelerometers are placed on the rear side of thebumper beam.

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Figure 3.32. Position of sensors in bumper (1: contact sensor, 2:accelerometers).

The contact sensor strip is placed in a groove in the surface of the foam between twolayers of a thin plastic material. The contact sensor is subdivided into elements, each100 mm wide. Each element has a number of switches and gives a signal if one ofthe switches is closed. This gives information about the width of the impacting object.It is also a first indication to the system that an impact is occurring, a so-calledarming of the sensor system. The accelerometers are placed 250 mm on each sideof the centreline of the car in order to get a good signal regardless of where theimpact is. The acceleration is integrated to a delta velocity. The maximum valueduring a chosen time period after first contact with the contact sensor is used. Thisvalue gives information about the stiffness of the impacting object, whether it is a legor a pole for example.

The sensor proved to be able to discriminate between different impacting objects.Figure 3.33 shows a sort of normalised sensor signals performed at 25 km/h. A cleardifference can be seen between the sensor output signals for the different impactingobjects. The smallest ratio between the lowest pole value and the highest leg valuewas a factor of 2.6. The tests at other impact speeds showed the same pattern. Inthe 20 km/h and 30 km/h tests, the lowest ratio was 1.8. The line separating thehighest leg values from the lowest pole values could therefore also be drawn for the20 km/h and 30 km/h test conditions. This line is however velocity dependent. At20 km/h it is at a lower level and at 30 km/h at a higher level than at 25 km/h. At30 km/h the bumper beam structure started to yield in some tests. Also in two25 km/h tests permanent deformation of the bumper beam occurred. In those tests

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the sensor output was much greater than in the tests, in which the bumper beamremained intact. Therefore, the ratio pole to leg form signals were much greater than2, ranging from 4 up to 18.

Figure 3.33. Sensor tests at 25 km/h

In all the tests with the active bonnet (refer Figure 3.34), the HIC value was belowthe threshold level of 1000. The highest active bonnet HIC value was 778, comparedto the standard bonnet values ranging from 877 to 7056. The reduction in HIC valuesranged from 18 to 90 %, where the highest values decreased the most. Also the testperformed on top of the lifting point resulted in a HIC value below 1000 (774).

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Figure 3.34. Head-impact results at 40 km/h (25 mph) using the proposedEuropean test limit with a standard hood and with an active hood from Autoliv.

HICPointStandard Active

Reduction

Above suspension 16497 1213 -92%Table 3.4. Results from head form tests at 50 km/h, comparing the active

bonnet with the standard bonnet.

3.6.3.4 Time flow of hood deployment

Figure 3.35 shows a crash test with a pedestrian dummy and a complete car frontwith the protection system installed. The bonnet lifting devices are activated atapproximately 30 ms after the impact and the bonnet is fully raised at 70 ms. This

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test was run at 40 km/h. A prior test was run at 30 km/h. In both tests, the bonnetstayed up until the head impacted the bonnet.

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Figure 3.35. Crash test in 40 km/h with a pedestrian dummy and an activebonnet.

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3.6.4 Active bumpers concepts

The idea of constructing active bumper systems is not really new, but as crash-activeones. They only make sense if they deploy before a collision and a collisionespecially with pedestrians is difficult to predict. Actual development is only instarting position. In the lack of realised solutions this article will show a collection ofinventions and aspects concerning the development of active bumpers.

The main concept of protecting pedestrians in accidents with cars is to avoidhazardous contact between the pedestrian and the car. This includes themodification of fall trajectories in order to prevent the head�s impact on a hardsurface.

There are several ways of reducing the effect of a pedestrian�s impact on a car�sfront end.Three of them will be described in the following:

1. The first way is to soften the impact by using exterior airbag systems. Thistopic will not be dealt with in this paragraph.

2. The second way is to increase the absorption distance. In this case the totalfront-end section is deployed and is moved into the front direction.

3. The third way of protection aims to deviate the contact of car and the legs of apedestrian into a vertical direction and to limit the knee flexion. This can bedone by deployment of only a low part of the front-end section.

Figure 3.36. Example of an active bumper system [6]

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When the front-end shape of the car is adapted to enhance the impact position ofpedestrians it must be considered that the fall of small people is different of the onefollowed by tall people.

P3 Dummy (3-year old child), the car front-end optimisedfor EEVC-Tests

HII Dummy (50%-male), the car front-end optimised forEEVC-Tests

Figure 3.37. Impact of a 3-year old child (P3) and 50%-male dummy (HII) on ahood [WEB00]

For both the second and third way of protection there are two solutions to deploy aprotection mechanism. The first possibility is an irreversible deployment with anexplosive charge comparable to airbag systems.

The second possibility is a reversible deployment system. This could be a electro-hydraulically driven system.

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3.6.4.1 Crash active and non crash active bumper systems

Active bumper systems can be divided into crash active systems and non crashactive ones. Like it is mentioned above the main problem in the development ofcrash active protection systems was that sensor technology and computertechnology was not able to deal with the problems of pedestrian recognition. Todaythe point where it is possible to do first steps into the direction of crash activepedestrian protection systems seems to be reached.

In spite of this all crash detection units share the problem of reliable detection. Thebiggest difficulties lie in the boundary region of a possible crash and an avoidablecrash which is the most interesting region for pedestrian protection.

As long as recognition systems are not able to work reliably in this region atemporary solution could be to use active bumper systems only in situations of heavycollision. Due to the better predictability of the behaviour of these objects this wouldmean to use active bumpers when two vehicles collide or a vehicle tends to run intoa stationary object.

Anyway a criterion for the moment of deployment is obstacle�s and car�s momentaryspeed. The driver�s reaction time influences the deployment too. This means withincreasing speed the recognition moment is shifted to an earlier point of time beforethe collision.

Today�s way out of the danger of false deployment could be the development of noncrash-active pedestrian protection systems, because these can renounce at obstaclerecognition systems.

Modern vehicle networks like CAN and LIN can provide the bumper�s control unitwith needed information about the car behaviour. Especially the vehicle speed isessential for the momentary adjustment of the bumper. In adaptation to the speedthe bumper can move into a position that is suitable to prevent a pedestrians head toimpact on hard vehicle parts like the A-pillars or to enhance the car deformationzone. The set-up of a real bumper will have to be found in simulations and try-outs.

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3.6.4.2 Possible Concepts

Active bumpers need a device that drives them to their extended position. Thefollowing paragraphs will show various possibilities how actuating mechanisms canbe realised.

3.6.4.2.1 Pneumatic drive

This protection system is similar to exterior airbag systems and shows off similardifficulties. In contrast to a usual airbag this system has a solid sliding casing aroundthe airbag.

In comparison to an airbag without a case it has the advantage of a defined shapewhat could be used to produce a well defined collision process. In reverse it has thedisadvantages of a harder surface and the same difficulties in recognising dangeroussituations like any exterior airbag system. On the one hand the reaction time ofrecognition systems is extremely short, because people�s behaviour is difficult toforesee for more than a fraction of a second. On the other hand false deploymenthas to be avoided by all means.

With view on quick bumper�s movement the big advantage of pneumatically drivensystem is that the moving part of the bumper does not have to be too solid, whichmeans not too heavy, because the inflated cushion has a bearing function.

An inflatable bumper is depicted in Figure 3.38 as an example for realisation.

Gas generatorThis unit would contain an envelope with a gas generator that inflates the envelope.Because of the opportunity of producing gas continually this concept is well suitablefor non crash active systems. Adaptive to the car�s momentary speed the envelopecould be inflated or deflated which would result in an optimised front-end contour.

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Figure 3.38. Cross section of inflatable bumper [6]. Legend: 1: vehicle�scontour, 2: support, 3: guiding, 4: airbag, 5: gas generator, 6: pressure

measuring instrument.

For crash active systems the amount of gas that is available in a fraction of a secondis probably too small.

Air reservoirUsing an air reservoir that is inflated at engine start could eliminate the deficit oflimited amounts of gas. This is comparable to pneumatic brake boosters andpneumatic suspension.

Pyrotechnical, displacement principlePyrotechnical charges can be used as expendable gas generators. In comparison togas generators they can produce much gas in a short time. Concerning the activebumper�s function as well as the recognition system this concept would lead to aprotection system that is really similar to an exterior airbag system. Due to the non-reversible operation or the gas source this system can only be used in crash-activesystems. In interest of reliable inflation a number of small airbags should be usedinstead of one big bag. An alternative could be the use of one big bag with more thenone pyrotechnical charge. The Figure 3.39 shows front and rear airbags. Theassociated covers are removed in order to show the placement of the bags.

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Figure 3.39. Inflatable units at front and rear end [6]. Legend: 2: bumpers,4: airbags.

The kind of active bumper shown below uses pyrotechnical charges to generate gasthat drives pneumatic cylinders. Due to the irreversibility of the charges� activationthis concept is only suitable for crash-active protection systems.

Figure 3.40 shows an example for a complete deployment system including sensorsand control units.

Figure 3.40. Scheme of scanning and deployed active bumper system [7].Legend: 1: radar receiver, 2: wire, 3: radar transmitter, 4: computer, 5: speedsensor, 6: obstacle,7: frame, 9: pyrotechnical mechanism, 10: deformation

mechanism.

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Taking into account that the entire bumper is moved involves light weight design ofthe moving parts in order to guarantee short reaction times.

Pyrotechnical, reaction propulsionAn alternative pyrotechnical drive uses the reaction propulsion (refer Figure 3.41).The advantage of this concept is that if once activated it is possible to realise welldefined working duration without any electronic control. It has to be made sure thatthe hot exhaust gas does not injure someone and does not burn parts of the car.

Figure 3.41. Reaction propulsion drive for active bumpers [4]. Legend:7: support , 9: cartridge, 11: charge, 13: rod, 15: support, 17: nozzle, 19: stroke.

3.6.4.2.2 Hydraulic drive

The hydraulic drive is, if designed consistently, suitable for crash-active and for noncrash active protection systems as well.

In Figure 3.42 the crash bar is connected to the car�s body. If the superior systemsends the signal to deploy the crash bar two cams that hold the rod in rear positionare unlocked. As soon as the rod is released it displaces the crash bar to the frontposition. This kind of hydraulic driven active bumper works digitally, that means it hasonly two rest positions.

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Figure 3.42. Hydraulic active bumper [9]

The system described above is meant to be used crash-active. Like the inflatablebumper it could also be used in a continuously working unit. In this case it wouldneed some technical changes. The cams could be omitted and the hydraulic rammust enable linear motion.

To enhance the working speed of the rods the hydraulic systems needs high oilpressure. As the hydraulic rods are necessarily placed in the car deformation zonedamage can not be ruled out. This means that it has to be compromised betweenquick rod extension and people safety in the case of rod damage.

3.6.4.2.3 Electro hydraulic drive

In order to improve reaction time and to reduce the car hydraulic components,hydraulic control components of the bumper system can be replaced by electroniccomponent. The main result of this measure is a remarkable weight reduction.

Figure 3.43 shows a rod with locked rams. These rams could be controlledelectromagnetically. The speed of the release can be adjusted by the transmissionratio of the crank train.

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Figure 3.43. Electrical release unit of a hydraulic rod [9]. Legend: 16: housing,20: jack, 22: body, 24: stem, 30: package, 56: blocking, 57: broach, 58: block,60: flange, 62: guiding, 63: annular reinforcement, 66: wheel, 68: rod, 70: rod,

74: positioning stop, 76: complementary stop.

3.6.4.2.4 Mechatronical drive

In this concept the hydraulic components shown in the previous paragraph have tobe replaced by electromechanical and electromagnetic ones. The mechatronicalbumper is a prospect for the at least medium-term future, but as soon as sufficientpower supply is available in cars, the development could go on.

Pneumatic or hydraulic lines leakages and environmental contamination bydischarged hydraulic fluid would be a part of the past. Dysfunction of electriccomponents should be easier to detect then small leaks in pneumatic and hydrauliclines. Additionally the implementation of redundancy is easier. The precision ofpositioning in combination with the low wear of contact less positioning systemswould still increase the reliability of mechatronical systems. As a consequence, theirreliability should be even better than the one given by hydraulic systems.

This mechatronical concept seems to be suitable for non-crash-active protectionsystems. The mode of operation of these bumpers would be comparable to theearlier mentioned continuously working protection systems.

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The suitability for crash-active operation is poor. Although the reaction time ofprovided actuators is good, it is difficult to realise quick shifting combined with longshift ways.

3.6.4.3 Summary and Prospects

The crash bar and its suspension have to be solid enough to absorb a crash�senergy. On the other hand a crash-active system has to be moved as quickly aspossible. This means that stress has to be laid on lightweight design. This is valid forthe energy absorbing components as well as for the driving mechanisms.

There are several suitable concepts for the extension of active bumpers. Due to theopportunities of weight saving and future development potentials the most promisingapproaches seem to be pneumatic driven systems and mechatronical drives thathave still to be developed.

The main problem in building active protection systems will remain the ability offoreseeing human behaviour. A pedestrian protection system has to react as soon asa danger occurs. It has to deploy a certain time before a collision, but it must bemade sure that it does not deploy if a crash is still avoidable.

As a matter of fact today�s most effective way of protecting accident�s victims fromserious harm is to avoid a collision. If this is not possible at all, the best opportunity isto reduce the impact speed. As it will be mentioned in the chapter below the severeof injuries is proportional to the square of the impact speed. In reverse a reduction ofspeed to the half amount reduces the car�s energy to a quarter of the originalamount.

Without an impact speed reduction all protection systems will not be able to preserveserious injuries. Even if the legs of a pedestrian are protected through theverticalisation of his fall trajectory he still can hit his head when colliding with thewindshield or rolling down the car�s roof. The basis of all future development has tobe the intensified improvement of braking systems.

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3.6.5 Enhancement of driver's view

Travelling by car under poor visibility conditions is a dangerous thing. While thevolume of traffic is only 20%, the rate of mortal accidents during night hours is about40% of all.

Low beam headlights have a range of 120 m at maximum and have to compromiseon good and glaring lighting. To avoid glare hazard there are proposals to lightstreets with polarized light or UV-light. Due to the weak efficiency those ideas weren�tbrought to realisation. Active and passive systems that detect IR-light seem to bemore promising.

In the same direction lies the enhancement of today�s headlamp technology.

If poor sight is not caused by darkness but by rain, snow or dirt that is thrown on thewindshield it would be useful to have sensors for automatic wiper control andautomatic headlight activation or adjustment. These could be supported by moisturerepelling glass surfaces.

Coming to constructional features it would be possible to improve the driver�s view byincreasing the fraction of sight through material on the passenger cell. An examplefor this is the Volvo Security Concept Car which has frame worked a-posts withPlexiglas filled frames and b-posts that are outlined in a view enhancing way.However, this concept will endanger the occupants in case of rollover.

These technologies are useful to guarantee a good view to the traffic situation.Invisibility of obstacles or pedestrians can be reduced by the four techniquesdescribed in the following.

3.6.5.1 Technology of rain sensors for automatic windshield wiper control

Most of all rain detectors in the automotive domain are using light emitting diodes(LED) and light sensitive diodes for rain recognition. The rain sensor is locatedbehind the windshield that means inside the vehicle (refer Figure 3.44).

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The transmitter LED (see Figure 3.45) transmits light or infrared radiation. Theemitted radiation is directed through the windshield glass. The external surface of thewindshield reflects the radiation directly to the receiver diodes due to total reflectance(interface glass � air). The intensity of the radiation can be measured.

Figure 3.44. Rain sensor: Localisation of transmitter LED and receiver diode.

In case of a totally dry windshield (no rain) the receiver LED receives approximatelythe full emitted intensity in fact of the total reflectance. Consequently it is necessaryto adjust the angle between radiation direction and the windshield surface to get100% of reflection.

In the other case of rain water drops or a film of water are located on the windshield.Due to the totally different refractive index no total reflectance occurs. The result isthat the radiation will be divided into two parts. One part of the radiation goes throughthe windshield glass into the environment and the other part can be measured by thereceiver LED.

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Figure 3.45. Principle of rain detection by reflection measurement techniqueson the windshield.

An electronic control unit (see Figure 3.46) calculates the difference betweenmeasured radiation in case of rain and the value of radiation in case of drywindshield. That value is the base to control the wipe intervals or the wipe velocity ofthe windshield wipers depending on the heaviness of the rain.

Newly, most of rain sensors are operating in the domain of infrared radiation insteadof visible light. This is the reason because the newer rain sensors can be locatedbehind the non-transparent parts of a windshield glass (e. g. behind the black partsof the glass). Therefore, the rain sensor can be integrated invisibly.

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light conductor heating

windshield raindrop optical connection

electronic

aperture

photo diode light emitting diode

interface

Figure 3.46. Detailed structure of a rain sensor.

3.6.5.2 Rain Repellent Windshields

One classic of nanotechnology is the so-called lotus effect, which due to a specificsurface structure makes self-cleaning surfaces possible. The water droplets rollingoff the water-repellent surface clean this surface by simply carrying awaycontaminating particles. The model for this technique is the leave of the lotus plant(refer Figure 3.47), which thanks to micro naps and a sophisticated run-off systemcan effectively use rainwater for cleaning and carries it off together with the dirt.Sanitation, roof tiles, windows and car lacquers can thus be improved. At the sametime, cleaning efforts and chemicals can be economized.

Lately advances in nano layers have made possible to develop water-repellingwindshields. Nano layers of silicon are used to reproduce the lotus effect(http://www.ptb.de/en/blickpunkt/nanowelten/lotus.html).

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Figure 3.47. Even water-based adhesive drips off the lotus leave (photo: Prof.Barthlott, University of Bonn)

This technology is currently in use for the windshield glass in the BMW Z8 Coupé[FIR99].

3.6.5.3 Headlights

In the past constructional effort has led to the development of modern halogen, gas-discharge and projection headlights.

Modern headlamps have reached a level where the brightness of emitted light has tocompromise with the danger of glaring oncoming drivers or pedestrians.

For the reason of stability and efficacy enhancement of headlight-bulbs with only onefilament and constant light level that is dimmed by flaps are under construction.An old idea that could not be sufficiently realised in former days is the use ofheadlights that are not fixed to one direction, but light the bending road.

An important field is the development of IR-headlights. IR-headlights can light thearea in front of a car up to 200 m without glaring the human eye. As many wellknown headlight systems have strong fractions of IR-light with wavelengths around

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1000 nm, combined with enhanced night vision systems they could lead to distinctadvances in driving security.

3.6.5.4 Active Night Vision

Passive night vision systems are described in chapter 3.6.6 �night vision�. Thosesystems detect heat that is emitted by creatures or machines and are used for long-range vision.

In contrast to passive systems, active night vision emits IR itself and detects thereflected fraction. From this point of view active night vision is similar to radar.

IR-light with a wavelength directly above visible light is of especially good use in nightvision systems. This IR-light is called Near-IR (NIR). A reason for the good suitabilityof this IR is the similarity to visible light. Many lamps produce NIR of wavelengthsbetween 780 nm and 1000 nm, many materials have similar characteristics for visiblelight and NIR and CCD-cameras and CMOS-cameras work with NIR.

Figure 3.48. Active night vision with IR-headlamps (photo: HELLA)

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The brightness of the NIR-picture depends on the distance between car andreflecting object. The nearer an object is the brighter it is on the picture. This meansthat a traffic sign is presented brighter than a far-off pedestrian. From the picture�sintensity the driver can�t take any information about the potential danger of an object.

Due to this reason active night vision systems are suitable to improve driver�s viewon short ranges. Because of their more specific picturing passive systems are ofbetter use for long distance sight improvement than active ones. [FRA], [MAZ99],[MIT00].

3.6.6 Night vision

The night vision system increases the range of sight during night driving and counterlight on country roads. It uses an infrared camera to detect the heat of pedestrians,bikers, animals and broken down cars. Because the extension of sight with thesystem is up to five times the normal distance, the driver can identify all objectsmuch earlier, react at an earlier time and avoid an imminent accident.

The following chapter describes the passive night vision system that is based on heatemitted by objects mainly.

In contrast to this description, active night vision will be discussed in the chapter3.6.6 entitled �enhancement of driver�s view�.

3.6.6.1 Physical basis

The use of infrared radiation based equipment in order to represent pictures is calledthermography. Mostly the kind of presentation is a black and white picture. There aretwo different possibilities for black and white presentation: �white-hot� and �black-hot�. That means, the objects are either white ahead of a black background or blackahead of a white background. In the case of use in darkness, the white-hot effect isbetter, because the objects appear brighter ahead of the darker background of theenvironment.

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Figure 3.49. Comparison of direct and IR vision (Valeo)

On mobile use it is desirable to have a large reach of corresponding radiation.Compared with near and middle infrared, distant infrared (also called thermalinfrared) has the largest transmission characteristic. Its range of wavelength liesbetween 5.0 µm and 1 mm. Also the wavelength range is ideal, because themaximum of radiation density is at ambient temperatures.

Thermal differences in the environment are generated into image signals byassistance of an infrared camera. These signals are finally represented on a virtualdisplay.

3.6.6.2 Current production application

At the moment the night vision system is installed only in a few production cars. Itconsists of two components: an infrared camera and a virtual display.

There are several possibilities to place the camera: behind the front grille, under therear edge of the hood or behind the windshield. Which position is used depends onthe type of car and size of camera.

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Figure 3.50. Infrared camera (Raytheon)

The virtual display which is called �Head-Up Display� (HUD) is a special screen thatis placed in front of the driver. According to the vehicle it can be placed atop theinstrument panel, as windshield HUD (see Figure 3.52) or like a sunshade.Compared to other displays it has decisive advantages. First of all the scale of theHUD content is nearly 1:1. This eases the distance estimation to the object. Second,the virtual clearance between image and driver amounts two to three meters. Thatreduces the work of the eyes and thus the fatigue of eyes and driver. The HUD iseasy comprehensible and does not stress the driver.

Figure 3.51. Two examples of head-up displays. Left: IR camera imageprojected, Right: Navigation data, speed information and object information

projected.

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In comparison to these so-called passive infrared systems, where no extraillumination of the scene is necessary, active infrared systems are possible. Activeinfrared systems need an additional headlamp for illumination of the observation areain front of the vehicle. The following picture shows such an extra-component.

Figure 3.52. IR filter in headlamp (Valeo)

3.6.6.3 Further development and prospects

Market researches give information about improvements for the night vision system.

Customers desire for example a bigger image cut-out and a better curve tracking.Corresponding solutions are in process.

Car manufacturers see great store by other points. For them aesthetic and economicaspects are as well in front as ergonomic and required space aspects.

By the system layout there are conflicts between a wide view angle and a large reachin case of the camera and between the 1:1 presentation and the limitation of requiredspace in case of the HUD. That means a wide view angle reduces the possibilities ofdetecting objects and lies to problems with required space by the HUD. Because ofthat these conflicts have to be studied for each vehicle in order to find an optimum forthe special types.

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The development of a mirror HUD has the advantage to show several otherinformation of interest (e. g. velocity or info of navigation in only one display). Thisaspect is of great interest for customer�s acceptance as well as for reduction ofaccident risk.

The future of this night vision system lies in image processing as well as in fusionwith other sensors.

At the moment it is not a real safety system but a good driver assistance system thatoffers a great benefit in subjective safety [BÜT02].

3.6.7 Driver Warning

A very interesting protection approach is to inform the car driver about thedangerousness of the actual situation. This is called driver warning methods. A bigadvantage of the warning strategies is that the car driver will be pointed out to thevulnerable road user and can drive manoeuvre himself to avoid the collision. Therequirements for the actuators are very low. An example of the general set-up isdepicted in the following figure.

Figure 3.53. Example for driver warning system.

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3.6.7.1 Warning signals

An emergency signal paradigm is usually one where two components are operatingin tandem.

The first component consists of a mechanical device that uses sensor logic todetermine if and when to trigger a signal [GET95]. It involves proper setting of thesensor decision threshold. If the criterion is set too strictly, false signals will beminimised, but there is the possibility that dangerous situations will go unsignalled. Ifthe criterion is set too leniently, fewer dangerous situations will go unsignalled(missed signals), but the false signal rate will rise. The solution to this dilemmarequires designing the physical components of the system to optimise the trade-offbetween minimised false signals and maximised sensitivity.

The second component of an emergency signal response paradigm is the humanoperator, who is responsible for detecting, evaluating, and responding (or notresponding) to the signal that is generated by the sensor-based signalling system.Consideration of the second component is necessarily a more complex process thanmanipulating the first component, due to the cognitive and perceptual processes ofthe human operator.

Warnings are artefacts [EDW94]. They are representations of the situations to whichthey refer.

Most warnings serve two functions. These are the alerting function, which issomewhat abstract, being emotive, or motivational, or both, and the informingfunction, which is more explicit. E. g. an auditory warning, contains no information atall beyond the fact that something has gone wrong. Vice versa, e.g. a warning textmay contain minimal iconic information, but may contain lots of information.

Our knowledge of the situation in which the warning occurs is also relevant [EDW94].Together the factors which have an alerting function can be seen as the iconicaspects of warning. Such aspects act almost instantaneously and require littleconscious information processing. Generally, one of the aims of a warning is toproduce a rapid alerting response, which is appropriate to the product or situation.

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The alerting function results from more than just e.g. the signal word, but results fromthe entire warning-in-context.

3.6.7.2 Criteria of warning effects

"A warning is rated information" [KOP98]. A good warning should include: Element which attracts the attention Reason for the warning Consequences if the warning is not observed Instruction for actions

There are different false warnings [KOP98]: Time dependent false warning: too early, too late Logical false warning: no warning in critical situation and vice versa Qualitative false warning: too many, too less, too strong, too weak

3.6.7.3 Categorisation of warning signal failure

Pritchett [PRIT97] investigated the pilot's non-conformance to alerting system. Pilotnon-conformance changes the final behaviour of the system, and therefore mayreduce actual performance from that anticipated.

The pilots� perceived need to confirm the alerting system�s commands may involveseveral factors, including:

The pilot may be concerned that the alerting system will fail to act as it should. The pilot may feel the alerting system cannot consider relevant information or

has different objectives. The pilot may place greater confidence in his own decisions than in the

alerting system�s.

This pilot non-conformance can be associated with following reasons for warningsignal failures:

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False signals: In theory, most design and training for emergency signals isbased on the assumption that when presented the signal is authentic and thusheeded. However, false signals may result as the product of an over-sensitivesensor system (conservative decision criteria) [GET95]. In many cases, agiven signal may be correctly generated based on a threshold violation, butmay be invalid or insignificant given the specifics of the operational situation.Such inappropriate signals may create a nuisance that diverts operatorattention. Elimination of all false signals is ideal, but attempts to achieve thatgoal by altering sensor detection decision criteria can lead to overly strictdetection systems that fail to signal true emergencies. Instead, it is thehuman�s responsibility to make the appropriate response decision.When the alerting system is designed to prevent catastrophic events in theavionics, variance in the sensor measurements and unpredictability in thesystem dynamics requires its reasoning to be conservative [PRIT97]. While aconservative design helps ensure prompt, adequate reactions to dangeroussituations, it also increases the frequency of false alarms and excessivecommands from the alerting system. Although the alerting system isperforming to specifications, false alarms may appear to the pilot as failures ofthe system.

Missing signals: Failure of signalling systems may take another form: insteadof generating spurious signals, they may fail to inform about legitimate danger.In many of these cases, the problem may be related to the first component ofthe signalling system: the mechanical sensor [USH94]. If the sensor�s decisioncriterion (tolerance level) is set too strictly, then the sensor may.

3.6.7.4 Recommendations

The basic properties of the human "sub-systems", which have to be considered indeveloping warning systems in vehicles, are [STE2001].

1. There is considerable human variability in height, reach and strength.Design such that systems are physically big enough for a large male to useyet are still usable for a small female who may have limited strength andreach.

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2. Human performance in sustained attention tasks is poor in comparisonwith machine sensor systems. Warning systems should be designed not tobe reliant on the driver maintaining a continuous awareness of the systemstate or road conditions.

3. People can detect detailed information in a relatively small area in thedirection they are looking, the visual area outside of this �foveal� region ismore sensitive to movements and flashing lights and can involuntarilyattract the drivers� gaze. Average glance duration should be less than1,2 s. No glances should be longer than 2 seconds. Total task time shouldbe less than 15 seconds.

4. People have limited colour recognition. Avoid using too many colours inwarning systems displays to support good discrimination of information.Preferably, three distinct colours should be used and not more than 10.The need for blue-green or white/yellow discrimination should be avoided.

5. The vehicle is a relatively noisy environment, and human hearing decayswith increasing age, particularly at high frequency. Caution should beadopted in the pitch, frequency and use of auditory warnings.

6. Humans can react quite slowly to warning systems that must providereasonable time for the human to respond to a signal. Under optimalcircumstances, assume one second is required; more realistically providethree seconds or no need to respond in a rapid time frame.

7. The driver�s ability to react to and respond appropriately to warningsystems operations will be affected by their fundamental level of drivingtask capability. The warning systems should not compromise driver safetyparticularly during periods of high task workload.

8. Some individuals adopt a level of risk that is personally acceptable and ifthe situation is perceived to be safer, it has been suggested that they willundertake riskier activities, e.g., faster driving and shorter headways.Design of warning systems should recognise the variation in personallyacceptable levels of risk.

9. Humans have limited short-term memory. Systems should not require theuser to remember or recall more than seven items in order to operate aninterface or resume operation of the system.

10. Errors will be made by users and should be considered in the systemdesign. Warning systems should be designed to be tolerant of humanerror.

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11. Humans have automatic reactions and expectations when interacting withmachines and with the environment. Warning systems should allow forthese that controls and displays behave in a manner that meets withexpectations.

12. Humans and machines both have strengths and weaknesses. Allocatefunctions between the human and warning systems to exploit the tasks thateach can undertake effectively to optimise overall system performance andenjoyment.

The general conclusions from the comparison of visual and auditory displays forwarning messages in vehicles are that short important warnings are basically betterpresented auditory if any complex information content can be transferred later orvisually, the message is repeatable, the signal-to-noise ratio is sufficient and if theannoyance effect can be reduced. Similarity, in the context of vehicles with complexsubsystems, high priority should be given to tactile warnings.

3.6.8 Pedestrian warning

It is necessary to clarify the wording at first. Pedestrian warning is a term, which issometimes misunderstood. Sometimes people talk about pedestrian warning, butwhat they are had in mind is driver warning. This inaccurateness can be observed inmany publications. If the term pedestrian warning is in use in this report, it meansthat the vulnerable pedestrian located on the road will be warned by a specialcomponent installed on the vehicle.

Dangerous situations can be differentiated into two most important situations: dangerous situation, where the car has normal speed and a collision with

pedestrian has big probability, Alert situation where the car is at low speed, e.g. driving on a parking.

There are two kinds of signals to signal a pedestrian an arising danger: acoustic signals, Visual signals.

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Warnings can be differentiated depending on the kind of car control system: prevent, e.g. when moving backwards the car makes a noise, no matter if

somebody is behind the car or not, no detection system is needed, Intelligent, e.g. the car�s control system recognises something is in its the

way.

AcousticAlert situation Dangerous situation

(only intelligent warning) Beeping sound informs about a car

moving backwards (prevent). Cars, especially electric ones,

become increasingly quiet.Loudspeakers are amplifying soundin slow speed passages (prevent)

Car announcing �Attention, I turn left�,�Attention, I turn right� when movingon parking (prevent or intelligent).

If the car recognises something onthe way, it uses the signal horn(intelligent).

Acoustic signal when starting flasherlights could warn pedestrians.

Signal horn, differentiated volume orspecial �pedestrian horn�.

Table 3.5. Possible acoustic reactions to alert and dangerous situations

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VisualAlert situation Dangerous situation

(only intelligent warning) Static or/and flashing light for

backwards (prevent, intelligent). Additional flasher lights, visible

(prevent).

Using flash light. Increase brightness or flash rate

depending on distance. Special light effects, e.g. with yellow

or orange light.Table 3.6: Possible visual reactions to alert and dangerous situations

3.6.9 Electronic controlled Seat-Belt Pre-Tensioner

A pre-tensioner is a further device, which participate to passive safety. Its function isto limit slack from the seat-belt when a crash is detected. The slack reduction isbenefit for the occupant because the belt load during a crash is reduced. Of course,the ignition of pre-tensioners and airbags is completely linked, because thosedevices have to be well synchronized to offer an optimized protection. This devicehelps also to optimize occupant position for effective restraint capabilities of theairbags systems.

Of course, seat-belt pre-tensioners are not related to protect vulnerable road users(VRU), but to protect occupants. Actually this actuator needn�t to be described in thisreport. But due to the fact that this technology of these pre-tensioners can be ofinterest for the car driver in case of automatic braking, this additional section wasincluded. In this case especially the reversible variant (so-called electronic controlledseat-belt pre-tensioner) is of interest.

In contrast to the pyrotechnical seat-belt pre-tensioner the electronic controlledvariant provides a reversible (reset able) deployment possibility. An example isdepicted in Figure 3.54.

A reset able pre-tensioning seat-belt retractor will remove slack from the belt and pullthe occupant into proper position in the seat. The system will include a motorizedretractor. The motor can be controlled e. g. by pulse width modulation (PWM).

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The reset able pre-tensioning seat-belt retractor will be able to help increase seat-belt comfort while also helping to reduce the probability of airbag-inflation-inducedinjury.

Figure 3.54. Reversible seat-belt pre-tensioner.

There is currently one European car manufacturer only on the market who haddecided to integrate reversible seat-belt pre-tensioners into cars. This was done byDaimlerChrysler in the PRE-SAFE system. PRE-SAFE gains advance warning of animpending collision due to unprecedented collusion between the active and passivesafety systems. PRE-SAFE is linked up to the anti-lock braking system, Brake Assistand the Electronic Stability Program (ESP), whose sensors identify critical drivingmanoeuvres and relay appropriate messages to the control units of these standard-fitted active safety systems.

PRE-SAFE belt tensioners return to their original status if the accident is averted.The precrash protective measures initiated by PRE-SAFE ensure that by the time anaccident takes place, the seating position of the occupants has been optimised andthe seat belts and airbags can operate more effectively. In other words, PRE-SAFEis not intended as a substitute for the tried-and-trusted restraint systems such as thefront airbags, belt tensioners, side bags and window bags but as a complement tothem. It does not encroach on their operation and efficiency in any way.

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If the accident is prevented, the advance tensioning of the seat belts is automaticallyterminated and the occupants can reset the seats and the sunroof to their originalpositions. This reversible design means that PRE-SAFE is instantly ready to go intoaction again if required.

Emergency braking triggers pre-crash activation of the belt tensioners. If the BrakeAssist system on board the S-Class carries out an emergency braking operation, thePRE-SAFE system is triggered too, and takes appropriate precautionary measures:

Figure 3.55. Reversible seat-belt retractor and its force diagram.

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The reversible PRE-SAFE belt tensioners prevent the driver's and front passenger'sbodies from moving too far forward during braking. The belt tensioner, driven by apowerful electric motor, can reduce the belt slack within just 120 milliseconds. Theengineers have carried out measurements which show that the forward movement ofa front passenger who was not expecting sudden emergency braking is reduced byup to 150 millimetres.

3.7 Rules for road constructions to guarantee the visibility and safety ofVRU

3.7.1 Problems and solutions

Accidents between motor-vehicles and pedestrians are not only caused by motor-vehicles and their drivers, however it is necessary to change the habits in daily streetuse.

It is also important to make changes in town-planning in order to reduce the risk ofaccidents. The following paragraphs are intended to inspire creativity in this area.

Problems and Solutions concerning pedestrian accidents [PRO01] are listed in thefollowing.

Problem Accidents caused by young drivers:The rate of 18 to 24 years old in fatal traffic accidents is 22 %. Therate of these persons in population is only 8 %. In comparison withthe 25 to 34 years old group is the risk to get killed in fatal trafficaccidents tree times higher. In comparison with the 35 to 54 yearsgroup is the risk five times higher. This general problem occurs inthe area of pedestrian accidents as well.

Solution Young drivers have very little driving experience, especially in criticalsituations. They need more driver-education, for example specialaccident-prevention-training as offered by the different drivers clubs.

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Problem Pedestrians who get out of bussesSolution Especially in the vicinity of school buses there should to be a station

that is separated from the street, with the possibility to get in and outof the bus without a step.

Problem Drivers that don�t keep 1 m distance from the kerb.Solution Where possible keep 1 m distance between roads and footpaths. Or

make a side stripe 1 m away from the kerb like it has to be inGermany (Kammergericht Berlin, AZ 12-U-785/90).

Problem CyclistsSolution Cycle paths; Improved technical equipment for cyclists, improved

training, especially for children.

Problem Stagnation of the sensibility towards pedestrians in road trafficSolution Continual safety instruction. There is a lifetime learning procedure

Problem Accidents with ChildrenSolution Better street planning (speed limits, blind corners, safe crossing

points, etc.) more regards to the needs of children (refer also chapter3.7.2).

3.7.2 Safety strategies in urban areas of Europe

In Europe several strategies for increasing safety in urban areas were investigated.One example is the German activity in this area described in [GDV01]. In this studyinsurance industry, research institutes and the police academy analysed differentmeasures to increase the safety. A special proposal for VRU protection in thisreference is the installation of street refuges for pedestrian crossings.

Further activities in this area coming from European countries like Austria, Denmark,the United Kingdom of Great Britain, the Netherlands and France are described inthe following paragraphs.

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3.7.2.1 Installation of an accident scene management in Austria

Approximately a quarter of all accidents occur on places where other accidents hadoccurred in the time before. So, there are accumulating regions.

In Austria the government had decided to collect all the relevant accident data to findout the accumulating regions [ÖST02]. They had defined a standard procedure tofind out and reconstruct these places. To be able to reconstruct the streets on thoseplaces with a minimised delay a close co-operation between the official departmentswas agreed.

The urban safety concepts have to be elaborated on the communal level in order toconsider the local needs. Under the support of the Austrian Federal Ministry of Traffican integrated demonstration project at a model community is going to be realised �the project should show a potential of possibilities to improve the communal roadsafety in the future. In Austria a big potential for that seems to be the design of cross-town links because there occur the majority of the traffic problems.

3.7.2.2 Developing of Urban Management and Safety (DUMAS)

The rural safety concepts also include measures for the rearrangement of the designof road space and for traffic calming all over the country. This is the part of theEuropean research project for �Developing of Urban Management and Safety�(DUMAS) to install the integrated safety management at the cities and thecommunities.

Road and Speed Classification Systems have been developed in Denmark, UnitedKingdom and the Netherlands as integrated parts of national guidelines for planningand designing of urban roads. A more detailed description can be found in[DUMAS9], [DUMAS12], [DUMAS13]. As an instance of a road and speedclassification system, the Danish one is roughly illustrated below. It has two roadclasses and a number of speed classes. Table 3.7 indicates a few basic andsimplified road layout recommendations for each road and speed class.

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Road class Speed class Examples of road characteristic90-110 km/h - Motorway, highway.

- VRU not allowed,- no parking.

60-70 km/h - VRU separated from motor traffic,- VRU crossings only at grade separatedor signalised junctions,- parking not allowed on carriageway,- limited access, no speed reducers,- 2-6 lanes, lane width 3,5m

50 km/h - VRU separated from motor traffic,- crossing facilities needed for VRU,- medium access,- no angle or perpendicular parking,- 2-4 lanes, lane width 3.00-3.25m

Traffic RoadMajor roads servingthrough going traffic andtraffic between urbanareas.

30-40 km/h - cyclists mixed with motor traffic,- pedestrians separated,- high degree of access,- no angle or perpendicular parking,- 1-2 lanes, lane width 2.75-3.00m

30-40 km/h - Cyclist mixed with motor traffic,- pedestrians separated,- high degree of access,- 1-2 lanes, lane width 2.75-3.00m

Local RoadMinor road servingonly local traffic ine. g. residential areas.

10-20 km/h - VRU mixed with motor traffic,- 'shared' areas,- motor traffic must give way,- 1-2 lanes, lane width 2.75m

Table 3.7. Simplified example of the Danish road and speed classificationsystem.

3.7.2.3 Efficiency of infrastructural measures for Pedestrian protection in France and the United Kingdom

The French company Orientations and the English research office TMS Consultancyhave carried out a study for establish an Efficiency of infrastructural measures forpedestrian protection in France and in United Kingdom in 1998 [ORI98]. This workwas organized by ACEA. Orientations and TMS have studied 150 and 196 places,

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respectively, where accidents involving pedestrians had occurred and where steps toimprove the road safety for pedestrians had been taken.

They have developed criteria relating to the urban environment and the volume oftraffic in order to obtain a representative selection of the different kinds of existingsituations.

MethodologyWithin the scope of the study the 346 sites (6 area types) were selected where11 types of infrastructural measures were introduced (see Table 3.8). During the3 years before and 3 years after the introduction of the measures, the statistics ofaccidents/ victims/ injuries are collected. The collected data were analysed andchecked by statistics from the point of view of reduction of accidents/ victims etc.assigned to the measures.

Additionally the calculation of saved social costs (scaled to 1 year) and cost forimplementation of the measures was made. The following values were calculatedand compared among each other:

the reduction of pedestrian victims first year rate of return (FYRR) severity index

Vehicles / Day < 7000 < 7000 < 7000 > 7000 > 7000 > 7000Pedestrian Presence limited medium high limited medium high

Number of Sites AreaType 1

AreaType 2

AreaType 3

AreaType 4

AreaType 5

AreaType 6

AllAreas

Measure TypeTraffic management 1 5 6 5 5 21Road markings 2 7 6 2 15Street lighting 3 1 7 5 2 15Refuge 4 1 7 12 2030kph zone 5 13 8 5 26Horizontal traffic calming 6 8 8 5 13 17 10 61Vertical traffic calming 8 21 12 1 6 5 45Pedestrian crossings 9 3 2 6 8 20 11 50Guard rails 10 2 4 16 14 36Packages (horiz./vertical) 11 1 9 1 1 5 17Traffic signals 12 5 15 20 40All Measures 62 46 28 55 90 65 346

Table 3.8. Overview of the analysed sites from France and UK allocated to areatypes and infrastructural measures

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For the analysis of the collected data, the following formulas are implemented:

victims(after) - victims(before)Reduction of victims =victims(before)

number of killed & severe injured victimsSeverity index =number of accidents

The parameter �First Year Rate of Return (FYRR)� act as indicator for evaluating ofthe benefit of the infrastructural measure for the first year after implementation. It isdefined to

saved costs due to the measureFYRR =costs for implementation of the measure

Example:The FYRR = 150% means the community saves social costs at an amount of 150%of the invested costs for the respective measurement (first year!).

For each area type and for each infrastructural measure the reduction of pedestrianvictims are calculated (see Table 3.9).

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Vehicles / Day < 7000 < 7000 < 7000 > 7000 > 7000 > 7000Pedestrian Presence limited medium high limited medium high

Drop of Victims AreaType 1

AreaType 2

AreaType 3

AreaType 4

AreaType 5

AreaType 6

AllAreas

Measure TypeTraffic management 1 -71% -38% -63% -28% -45%Road markings 2 -54% -48% -50% -51%Street lighting 3 0% -44% -36% -39% -39%Refuge 4 -40% -56% -34% -41%30kph zone 5 -58% -32% -52% -51%Horizontal traffic calming 6 -50% -17% -20% -33% -36% -55% -39%Vertical traffic calming 8 -69% -70% 0% -66% -55% -67%Pedestrian crossings 9 -91% -100% -39% -65% -57% -16% -49%Guard rails 10 -67% -68% -55% -26% -43%Packages (horiz./vertical) 11 -75% -24% -83% -80% -23% -29%Traffic signals 12 -52% -46% -36% -42%All Measures -61% -44% -40% -55% -49% -32% -46%

Table 3.9. Reduction of pedestrian victims of the single area types and due tothe single infrastructural measures.

The diagram below show the severity index calculated before and after theimplementation of the infrastructural measures for different measures types and fordifferent area types.

0%

10%

20%

30%

40%

50%

60%

MeasureType 1

MeasureType 2

MeasureType 3

MeasureType 4

MeasureType 5

MeasureType 6

MeasureType 8

MeasureType 9

MeasureType 10

MeasureType 11

MeasureType 12

All

"before" "after"

Severity Index of Different Types of Measures

Figure 3.56. Severity index of different types of measures.

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0%

10%

20%

30%

40%

50%

60%

AreaType 1

AreaType 2

AreaType 3

AreaType 4

AreaType 5

AreaType 6

All

"before" "after"

Severity Index of Different Area Types

Figure 3.57. Severity index of different area types.

Vehicles / Day < 7000 < 7000 < 7000 > 7000 > 7000 > 7000Pedestrian Presence limited medium high limited medium high

FYRR AreaType 1

AreaType 2

AreaType 3

AreaType 4

AreaType 5

AreaType 6

AllAreas

Measure TypeTraffic management 1 37% -13% -7% 101% 4%Road markings 2 131% 98% 534% 124%Street lighting 3 628% 793% 35% 88% 261%Refuge 4 1188% 1085% 90% 318%30kph zone 5 97% 62% -8% 73%Horizontal traffic calming 6 364% 33% 56% 2% 65% 106% 94%Vertical traffic calming 8 163% 50% 59% 127% 34% 96%Pedestrian crossings 9 994% 216% 288% 162% 208% 147% 249%Guard rails 10 21% 2035% 920% -75% 796%Packages (horiz./vertical) 11 19% 154% 420% 11% 15% 43%Traffic signals 12 177% 935% 216% 433%All Measures 183% 99% 24% 220% 187% 106% 145%

Table 3.10. Results of the FYRR-calculation of the single area types and of tothe single infrastructural measures

Results:The introduction of infrastructural measures results in:

Reduction of pedestrian accidents/ victims by 46% (killed: 63%, injured:severe 34%, slightly 34%)

Reduction of �non� pedestrian accidents by 30%

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Reduction of all accidents by 37% Drop of the severity index from 32% to 26% Savings of social costs of 200 Million � FYRR of 145% for all measures in all areas FYRR of single areas and measure vary, FYRR is linked to the suitability of

the measure to the local characteristics of the site Guard rails, refuges, street lighting and pedestrian crossings seem to be the

most profitable measures, FYRR over 250%, varies according to area type

Whatever their nature, and whatever the area type, studied infrastructural measuresare reducing the number of accidents and the number of victims. The amount ofreduction, and in particular the Rate of Return, varies, and seems to be closely linkedto the suitability of the measure to the local characteristics of the treated sites, andnot only to simple criteria of vehicle and pedestrian traffic volume.

Guardrails, refuges, street lighting and pedestrian crossings seem to be the mostprofitable measures in terms of economic return, with a rate of return over 250% theyear following the works, but their efficiency varies according to the area type.

3.7.3 Examples

In this paragraph, some examples are given to understand the problematic of theinfluence of the infrastructure. The examples are illustrated by a lot of pictures to getan eidetic impression.

3.7.3.1 Tunnel and Subways

In conformity with the German DIN standard 67524 Part 1 and 2 this is one of theexamples on how it is possible to make streets safer in simple ways. It could behelpful if different countries shared their experiences to develop international safetystandards for tunnels and subways.

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The following diagram (Figure 3.58) shows how light intensity can be graduallyreduced at the entrance of a tunnel in order to minimize the feeling of driving into ablack hole (www.strassenbeleuchtung.de/technik/tunnel.htm).

A = ApproachB = Insight areaC = Sight adjustment areaD = Inside areaE = Exit area

Figure 3.58. Siteco lighting engineering.

The following pictures illustrate the problematic of invisible vulnerable road users intunnel environments. In this example it is shown that VRUs can be overlooked by thedriver at the exit of a tunnel. A solution for this problem could be to increase thediameter of the tunnel in section E (exit area).

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Figure 3.59. Invisibility of VRU at the tunnel exit

Figure 3.60. Tunnel exit - View from inside the car

In addition to this there are some requirements from the VRU protection point of viewfor tunnel constructions:

If the diameter of the tunnel construction is increased at the entry points thenthe visibility of VRUs in this area is increased as well.

VRU

VRUnot visible

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Increasing the tunnel diameter or graduation of illumination at the entry pointscould increase the chance for the eyes to adapt to the changed light intensity.

3.7.3.2 Invisibility of VRU in case of parked cars

Parking areas are also potential locations for dangerous situations. As illustrated inthe following pictures the visibility of crossing pedestrians (e. g. children) isdramatically reduced. To avoid these critical situations a simple proposal is toincrease the distance between parking area and driving lane (see Figure 3.61 andFigure 3.62).

Figure 3.61. Cars blocking sight on pedestrian

VRU

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Figure 3.62. View from inside the car

3.7.3.3 Single-side illuminated road

Pedestrians on the unlighted side of the road are difficult to see (refer Figure 3.63).This situation is still worsened by the need of eye adaptation.

VRUnearly not visible

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Figure 3.63. Single-side illuminated road

3.7.3.4 School problematic

As everybody knows, the way to school sometimes is a dangerous way. Especially infront of the school building and if the school is next to a strongly frequented streetdangerous situations can occur. The town planning departments have to look for away to make streets safer.

Darkregions

Wellilluminated

region

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Figure 3.64. Children in front of a school building, far-off pedestrian crossing

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4. Identification of system concepts for VRU protection on vehicles

4.1 Success of pedestrian protection in the EU in recent years

The European Community has had impressive success in achieving the highestpedestrian protection level on the globe. In the years 1980 to 2000, the fatality rateper million inhabitants in Europe decreased by 65 % from 40 to 14 [DEK02].

The target set by the EU Commission in 1999 was to reduce pedestrian fatalities by30% and severe injuries by 17% by 2010. According to actual traffic data andstatistical expectations, this target will be reached without any European directiveand test procedure. This trend results from design measures, the influence of activesystems on the behaviour of a car during the pre-crash phase and is also due to roadsafety instruction programs.

In absolute numbers, the pedestrian fatalities in 13 EU member states dropped from14,631 to approximately 6,000. This means a reduction of about 60%. The samereduction can be assumed for the seriously injured pedestrians, based on theGerman national data.

Taking into account this constant decrease of pedestrian casualties over the last 20years, it can be expected that a further decrease of about 30% of pedestrian fatalitiesin Europe will occur over the next 10 years. These 30% correspond to the target setby the European Commission and will be reached without any ECE directive orregulation. In the following years the actual provisions on the car and theinfrastructural changing, for example traffic calming measures, will affect the futuretrend in a positive way. The same trend can be expected for the reduction ofseriously injured pedestrians. The target set from the EU commission is a value of17%.

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4.2 Evaluation of actuators

In chapter 3 many different safety concepts were described in detail from a puretechnical point of view. Interesting questions are now: Which of these safetyconcepts are really useful for the protection of vulnerable road users? Which is themost efficient one for protection of vulnerable road users?

To find the answer to these questions an evaluation of all of these actuators wouldbe helpful. Aspects like effectiveness, feasibility and side effects will determine theanswer. To perform this evaluation, a matrix is defined where actuators are listed onthe horizontal axis and criteria on the vertical axis (see Table 4.1). �+� indicatespositive evaluation level, �-� indicates negative level and �0� indicates neutral level.

In Table 4.1 six criteria are defined for evaluation:

Reversible/ Irreversible/ No Deployment:The type of deployment of actuators is very important to distinguish, whichkind of actuators can be (realistically) triggered without (or with a very lownumber of) false alarms. Using today�s sensors and fusion techniques no100% fault safe deployment is possible. Consequently, non-reversiblesystems cannot be triggered with the required low rate of false alarms.Systems that can be triggered in a reversible way and systems, that don�tneed a deployment, make sense for VRU protection. Therefore, the SAVE-Usystem will base on reversible systems only.

Passive/ Crash-active/ preventive Methods:These three categories were defined very well in the chapter 3. For the SAVE-U project only systems that can be triggered by a sensor fusion processor areconsidered. So, pure-passive methods are really helpful for VRU protection,but are not part of this project.

Protection of VRU or occupants:It is easy to distinguish the protection effect between protection of caroccupants or VRU of actuators. For the SAVE-U demonstrators only VRUprotecting actuators are of interest.

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Protection potential from accident statistic point of viewAccident statistics are helpful to distinguish between actuators, that are helpfulor not. For example, it is possible to re-calculate the accidents in the accidentdata base in case of early (automatic) braking to find out how injuries orfatalities can be reduced or avoided. In other cases, some actuators arehelpful in a very small number of accidents only. These calculations can beused for selection the actuator that has a big positive influence in VRUprotection. Only the actuators that have a powerful protection effect are ofinterest for the SAVE-U demonstrator vehicles.

Avoidance or reduction of first impact:It is helpful to clarify which kinds of actuators are useful to avoid or to reducethe first impact vehicle versus VRU.

Avoidance or reduction of secondary impact (including tertiary impact):Parallel to the primary impact, the secondary and tertiary impact is veryimportant for the VRU to be considered [KOV99]. This criterion is oftenforgotten in technical papers or discussions. The secondary impact is thecollision between VRU and the infrastructure (e. g. road) after the impactbetween VRU and vehicle. In addition to the secondary impact the so-calledthird impact is defined. The third impact is the collision between VRU and asecond vehicle (occurs after the first and the secondary impact). There aremany accidents were the severity of injury of the secondary/ tertiary impact ismuch higher than the severity of injury of the first impact. Due to basicmechanical equations (like impact law) the secondary/ tertiary impact can bereduced only by reduction of collision speed.

This matrix gives the possibility of a very easy evaluation of the actuators by usingthe indicators. A ranking of actuators is possible by reading of the last row of thematrix, result of the evaluation. The actuators with the highest numbers (brakingdistance reducing measures, driver warning, and enhancement of driver�s view,pedestrian warning and night vision) are the most potential ones. The automaticbraking seems to be the most efficient actuator for VRU protection.

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Reversible/Irreversible/

NoDeploymen

t

Rev.

+

Rev.

+

Irrev.

-

Rev.

-

Irrev.

-

Irrev.

-

No

+

Rev.

+

Rev.

+

No

+

Passive/Crash-active/

PreventiveMethod

Prev. Prev. Crash-active

Pass. Prev. Crash-active

Pass.

Protectionof VRU orOccupants

VRU+

VRU+

VRU+

VRU+

VRU+

Occ.-

VRU+

Protectionpotential

fromaccidentstatisticspoint of

view

++ + + + + 0 +

Avoidance/reduction offirst impact

++ + + + + 0 +

Avoidance/reduction ofsecondary

impact

++ + 0 + + 0 +

Total: 8+ 5+ 2+ *) 5+ 5+ 0 5+Table 4.1. Overview about protection systems and their protection potential.

Legend: �+�: positive evaluation level, �0�: neutral evaluation level, �-�: negative evaluation level. *) valid for reversible variant only.

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The SAVE-U project is sensor-oriented, not actuator-oriented. Consequently, theactuators that will be integrated into the two demonstrator vehicles will be from thedomain of preventive systems. In the demonstrators, no actuators will be integrated,that are not deployable, because the sensor platform makes sense for deployableactuators only. In addition to this the general direction of this project will be to focusonly on reversible systems. Concluding, the SAVE-U demonstrators will havereversible preventive systems on board.

In Workpackage WP 10 �Building of prototypes and fitting on cars� a selection and adetailed description of SAVE-U protection systems will be given. The results will besummarised in the Deliverable D 22.

At the moment, it seems that automatic deceleration, driver warning and pedestrianwarning are potential candidates for SAVE-U demonstrators. To introduceDeliverable D 22 in Workpackage WP 10 a brief discussion about these potentialactuators will follows below.

4.3 Deceleration

From an accident research point of view the braking is the most efficient protectionsystem for vulnerable road users (see also chapter 3.6.1.3). The reason for this is,that severe of injuries is related to collision speed square (vCollision

2) in the relevantinterval between 30 km/h and 50 km/h SAVE-U focus on.

The following two figures illustrate the effect of deceleration on the collision speedand the collision speed square during the contact versus braking time. In both figuresfour selected situations are depicted for easy comparison: Initial speeds of 50 km/hand 40 km/h and deceleration of -1 m/s2 and -2 m/s2.

In the first diagram (Figure 4.1), it is highlighted that in case of initial speed of50 km/h, deceleration of -2 m/s2 and braking duration of 1 s the speed reduction is inthe order of 14%. In the same situation, but assuming initial speed of 40 km/h, thespeed reduction is increased up to 18%, approximately.

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Speed reduction by deceleration of 1 m/s2, 2 m/s2

0

10

20

30

40

50

60

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 1,3 1,4

time [sec]

v_0=50 kmh, a=-1m/s^2v_0=40 kmh, a=-1m/s^2v_0=50 kmh, a=-2m/s^2v_0=40 kmh, a=-2m/s^2

Reduction

14 %

Reduction

18%

Figure 4.1. Collision speed versus braking duration. Initial speed 50 km/h (bluelines), 40 km/h (green lines). Deceleration a = -1 m/s2 and a = -2 m/s2,

respectively.

The reduction of collision speed square is much more important than the speedreduction under the same conditions, due to the quadratic relation.

This is shown in Figure 4.2. For example, it is highlighted, that in case of initial speedof 50 km/h, deceleration of -2 m/s2 and braking duration of 1 s the collision speedsquare of the contact is reduced of 27%, approximately. In the same situation, butassuming initial speed of 40 km/h, the reduction of collision speed square isincreased up to 33%.

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Reduction of Collision speed square by decelerationof 1 m/s2, 2 m/s2

0

50

100

150

200

250

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 1,3 1,4

time [sec]

v_0=50 kmh, a=-1m/s^2v_0=40 kmh, a=-1m/s^2v_0=50 kmh, a=-2m/s^2v_0=40 kmh, a=-2m/s^2

Reduction

27 %

Reduction

33 %

Figure 4.2. Reduction of collision speed square vCollision2 during the contact

versus braking duration. Initial speed 50 km/h (blue lines), 40 km/h (greenlines). Deceleration a = -1 m/s2 and a = -2 m/s2 respectively.

Decrease of the collision speed square vCollision2 is directly related to the reduction of

severity of injuries (see Figure 4.3). Especially in the region of 30 km/h up to50 km/h, where the gradient of the curve has its maximum, the cumulative frequencyof MAIS 2+ casualties is nearly linear proportional to the collision speed. This intervalwas indicated in Deliverable D 1 as an operation area with a high potential, where itis expected to get the maximum of reduction in severity of injuries.

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Car-to-pedestrian accidents

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 10 20 30 40 50 60 70 80 90 100

collision speed [km/h]

Figure 4.3. Cumulative frequency of MAIS2+ casualties versus collision speed.

The objective of the SAVE-U demonstrators will be to brake with brake pressures inthe comfort braking area instead of emergency braking. This corresponds todecelerations of -1 m/s2 up to -4 m/s2. The SAVE-U braking system will not be ableto brake with 1 g (1 g = -9,81 m/s2 = acceleration of the gravity), which is a commonvalue in emergency braking systems. The braking concept on the SAVE-Udemonstrators bases on reversible actuator methods. This includes that rare falsealarms (e. g. false automatic braking), will not effect/ endanger third parties in thetraffic (e. g. following vehicles).

The advantage of using braking as an actuator system is twofold. First, the impact ofthe primary impact (so-called collision) will be reduced dramatically, as it wasillustrated in the figures above. In addition to this, the second advantage is, thatbraking is the only protection method which reduces also the impact of thesecondary impact (collision VRU versus street) and third impact (collision VRUversus second vehicle).

A big advantage of comfort braking is that it is a reversible method, of course, andthe deployment can include different brake pressures to find the optimal braking

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course with respect to measurement accuracies of the trajectory, and other technicalparameters.

4.4 Driver Warning Strategies

A basic principle in the community of driver assistant system engineers is: �It is muchmore effective for both pedestrian and host vehicle to avoid a crash, than to reducethe accident severity of a crash�.

Following this rule, in many critical road situations the possibility of the collision canbe minimised if the car driver is warned early enough. Then the driver is asked toreact directly: The eyes will be directed to the front immediately. Collision has a goodchance to be avoided with manoeuvre-driving.

The warning can base on three methods: acoustical, optical and haptical. Thetoday�s view is that the DaimlerChrysler demonstrator will have acoustical and opticalwarnings on board. For the Volkswagen demonstrator haptical warning is a potentialcandidate, which can be integrated, because the wake-up effect is very importantand helpful. For example, haptical warnings can be provided from two sources to thedriver:

Vibrating steering wheel. Hard braking jerk.

4.5 Pedestrian Warning Approaches

It makes sense to warn the pedestrian in a dangerous traffic situation as well as thedriver. The reason for this is the same reason as mentioned in the section 3.6.7entitled �driver warning� above.

But the selection is much more difficult to decide, which warning method is reallypossible. From a technical point of view using signal-horn or headlamp flashing canbe helpful in some cases to avoid a crash or to reduce the severity of a crash. But

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this is only the view from one perspective. Another perspective is the currentsituation of regulations. For example in Germany it is not allowed to automaticallyuse headlamp flashing or signal-horn for pedestrian warning.

Following these boundaries, pedestrian warning can be investigated in this projectonly on proving grounds, not in real traffic situations.

4.6 Impact on sensor specifications and system specifications

In this section general remarks on sensor specifications and system specificationsfor VRU protection on vehicles will be given. Examples of specification parametersare:

measurement resolutions of positions and dynamics measurement accuracies of positions and dynamics measurement rate (update rate) camera resolutions area of coverage overlapping areas of different sensors detection probabilities probability of false positives classification capabilities multi-target situation capability and further parameters

4.6.1 Sensor system specification versus application

In the following Table 4.2 some hints of specifications are summarised. It is verydifficult to fill out this table with �the correct�/ �the exact� values, because theparameters depends directly on the concrete realisation of protection systems andthe man-machine-interaction. Therefore, values in this table have to be understoodas examples or typical values coming from experiences in this domain.

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Maximum range 40 m 40 m 20 m 20 m 20 m 20 m 40 m

Minimum range 0 m 5 m 0 m 0 m 0 m 0 m 5 m

Detection probability

Probability of false

alarms

0 % 0 % 0 %

Classification

probability

False alarms in

Classification

0 % 0 % 0 %

Measurement Rate

(Update Rate)

20 Hz�

100 Hz

20 Hz�

100 Hz

20 Hz�

100 Hz

20 Hz�

100 Hz

20 Hz�

100 Hz

20 Hz�

100 Hz

20 Hz�

100 HzTable 4.2. Hints of system specifications for different VRU protection actuators(legend: = as high as possible (>>99,9 %); = as low as possible (<<0,1 %)).

4.6.2 Measurement accuracies � Maximum range

A very important requirement regarding sensor system performance is the accuracyof positions and velocities. The following calculations and graphs will provide animpression of what kind of accuracy is necessary to achieve the required accuracy ofthe trajectory for deployment.

In section 3.4 some equations and calculations regarding coverage area of sensors�field of view (maximum range) are given. It is obvious that a maximum range of 30 m

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up to 40 m is necessary to collect all data early enough before the crash occurs. It isalso obvious that a large coverage angle is required.

In addition to this mathematics, the descriptions in this section will focus mainly onmeasurement accuracies.

Typically, most of the sensors (e. g. radars or cameras) provide information aboutthe scene in a polar coordinate system ( R and parameters). Consequently, the

measurement accuracies of a single sensor measurement are given in a polarcoordinate system (e. g. standard deviations R and or variances 2

R and 2 ). A

normal statistical description includes also the cross-correlation between range andangle measurement. All these data are summarised in the so-called covariancematrix as follows:

22

22

R

RRC .

The values in this matrix are given by the sensor system. If there is no mathematicalcalculation available for this values, values can be derived from experimental tests(practical method).

It is clear that the risk assessment (deployment calculation) is based on Cartesiancoordinate system. The covariance matrix can be transformed in this domain byusing the following rule:

T

R

RR

yxy

xyxcartesian TTC 22

22

22

22

,

where T stands for the transformation matrix, which is the Jacobean matrixcontaining the partial derivations. TT indicates the transposed of matrix T . T can be

calculated by

)cos()sin()sin()cos(

RR

yRy

xRx

T .

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Using this statistical approach a graph of measurement accuracies (= standarddeviations R and ) at each Cartesian position ),( yx can be calculated, if the

polar standard deviations are given.

Example:Assuming the polar standard deviations of mR 5,0 and rad2102,53

(variances of 22 25,0 mR and 2322 107,2)3( rad ) the following position errors

can be estimated in the x - y -plane. Normally it depends on the measurement

principle and the concrete realisation of the detection algorithms of a sensor, if thecovariance values are zero or not. In this simplified example the covariance valueswill be neglected, radmmR 002 . Therefore, the result is much easier to

understand than assuming the �full� covariance matrix, which will be necessary forexact calculations.

Figure 4.4 provides a 3D-graph regarding the measurement accuracies in eachposition in the x-y-plane.

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Figure 4.4. Measurement accuracy of a single measurement in the x-y-plane.

It can be seen that the accuracy of a single measurement depends mainly on theposition of the object. Near objects can be measured in this example with anaccuracy of approximately 30 cm. Objects, that are located at 40 m (maximum rangeof coverage area in this example) can be measured with 2 m accuracy,approximately.

Figure 4.5 shows the accuracy of a single measurement on the x-axis only. Thepicture will be used in the following for comparisons.

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Figure 4.5. Measurement accuracy of a single measurement in x-direction(y = 0 m).

These two previous graphs give a feeling of what level of performance a single(isolated) measurement can provide in the x-y-plane with the assumptions describedabove. In Figure 4.5 it was assumed, that each measurement provides one result.Normally this is not that case, due to physical characteristics (e. g. wave propagationand multi-path propagation aspects) and characteristics of detection algorithms. Atypical mean value for the detection probability is about 70 %. Of course, objects,which are far, have a lower detection probability. Objects, which are close to thesensor, have a higher detection probability.

Figure 4.6 illustrates a typical measurement result. In this example, it was assumedthat there is an incoming object positioned on the x-axis (starting at 40 m distance,approaching up to 0 m distance). The black dots represent the real positions; theblue dots represent the measured positions. Further assumptions are: measurementtime = 50 ms, range accuracy = 0,3 m, angle accuracy = 3 °, vehicle speed= 50 km/h.

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Figure 4.6. Measured position assuming detection probability of 70 %.

But, the result of the tracked position over time is much more interesting. It is wellknown, that tracking will enhance the accuracy of a single measurement. Someexamples are shown below to give an impression of what kind of improvementstracking algorithms will provide.

The basic approach of tracking is to calculate a state estimation for eachmeasurement cycle )(~ tx which is based on two input vectors, first the measuredvector )(tx and second the prediction of the measurement before )(� tx . A commonly

used tracking filter in this domain is the Kalman filter. It is a so-called optimum filter,which minimises the estimation errors. But, to demonstrate to behaviour of a trackingalgorithms a 1st order recursive filter (so-called �filter) will be used in thisillustration. The estimation is

)(�)()1()(~)(~

)(~ txtxtytx

tx ,

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where stands for an adjustable parameter. The prediction can be calculated byusing a dynamic model (e. g. a model of constant velocity):

TTtvTtxtytx

tx )(~)(~)(�)(�

)(� .

After these basic formulas for the state vector, the focus will base on themeasurement accuracies. The question is, what is accuracy of the trackedtrajectory? The accuracies will follow the equation:

)(�)()1()(~ 22 tCinvtCinvinvtC .

This formula is not very demonstrative. So, using examples will help to understandthe results. The following Figure 4.7 provides some example trajectories, the exactones and the measured/ tracked ones. In this graph typical values for detectionprobability of p = 70% and filter parameter 5,0 are used.

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Figure 4.7. Measured position (blue) and tracked position (red) assumingdetection probability of 70 %.

It is obvious that the measurement accuracy will be enhanced by tracking. Theenhancement of tracking is quantified in Figure 4.8. This figure shows the accuracyof a single measurement (blue line, refer Figure 4.5) compared with a trackedtrajectory (red line) if a detection probability of 100 % is assumed. Real detectionprobabilities are lower; consequently the enhancement of a real sensor system willbe located in between the blue and the red line.

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Figure 4.8. Accuracy of a single measurement (blue) and theoretical trackaccuracy (red) assuming detection probability of 100 %.

Summary:High measurement accuracy is very important to be able to trigger the deploymentsignal for actuators. The example given in section 3.4 shows that an automaticbraking system has to be activated at approximately 20 m distance to the object if avehicle speed of 50 km/h is assumed. To avoid unnecessary warnings to the driver,a high probability for a collision is necessary for deployment. Consequently, hightrajectory accuracy has to be achieved at 20 m. The trajectory accuracy must belower (that means: better) than the vehicle�s width.

Maximum range versus braking acceleration:The maximum range depends on different parameters. Of course, one parameter isthe quality of the trajectory as discussed above. In addition to this, the trigger timebefore contact is a second important value.

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The objective of this section is to illustrate the relation between braking accelerationand maximum range. This will be shown in the following Figure 4.9 by continuing theexample introduced above.

Maximum range versus initial speed

0

5

10

15

20

25

30

35

Initial speed [km/h]

maximum range (a=-1m/s^2)

maximum range (a=-2m/s^2)

maximum range (a=-3m/s^2)

maximum range (a=-4m/s^2)

maximum range (a=-5m/s^2)

maximum range (a=-6m/s^2)

maximum range (a=-7m/s^2)

maximum range (a=-8m/s^2)

maximum range (a=-9,81m/s^2)

Figure 4.9. Maximum range versus braking acceleration(a = -1 m/s2 � -9,81 m/s2).

The result of these basic calculations is, that a maximum range of 35 m seems to benecessary. In real operating systems a safety margin could be necessary. Themaximum range of 35 m - 40 m seems to be a good choice. The same value is alsomentioned in [MEN02].

4.6.3 Time scheme for deployment of warning signals or automaticdeceleration actuators

First information regarding the time scheme for deployment of warning signals orautomatic deceleration actuators were already provided in section 3.4. In this section

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much more detailed calculations will be given. The same nomenclature will be usedas in section 3.4.

The trigger for the deployment will be generated if the time-to-collision (TTC) is equal(or lower) than the required deployment time of the actuator:

ActuatorofDeploymentforTriggertTTC ActuatorDeployment ,

In addition to this requirement above, it could be helpful, if further criteria have to befulfilled to start the trigger signal. This depends on the specific characteristic of theactuator under consideration. For example, for the deployment of driver warningsystems (e. g. acoustical warning) the parameter ActuatorDeploymentt , is not so easy to

determine, because this value will be influenced by additional requirements fromdriver acceptance.

It is not planned to use a non-reversible protection method in the SAVE-U project.But also in this cases the deployment criteria should be modified, for example like thefollowing equation determines

ActuatorofDeploymentforTriggereunavoidablisCrashtTTC ActuatorDeployment )()( , .

The distance between the observed dangerous object and the host vehicle DeploymentR

at the moment of deployment the actuator is given by the equation

ActuatorDeploymentDeployment tvR , ,

where v stands for a constant collision speed.

Example:The SAVE-U demonstrator vehicles will have an electronic controlled brake boosteron board. From an accident research point of view a good protection potential forvulnerable road users (VRU) is possible if the brake trigger will be provided 1 sbefore the contact. Assume that the deceleration is in the order of 1 m/s2 and theinitial speed is 50 km/h (= 13,9 m/s) the deployment range is

mssms

smtatvR ActuatorDeploymentActuatorDeploymentDeployment 4,13)1()1(

2119,13

21 2

22

,, .

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The object range at the moment the tracking starts is much more farther away. It canbe calculated by

)( ,ActuatorDeploymentTrackingTracking ttvR .

If we assume that the tracking needs N = 10 successful measurements for a stabletrajectory (typical value for radar systems), the detection probability is p = 0,7 and themeasurement rate is f = 20 Hz the value for TrackingR is given by:

ActuatorDeploymentActuatorDeploymentTrackingTracking Rfp

NvRtvR ,,

mmsmR

sTracking 3,234,13

207,0109,13

1.

Following the description above the required detection range nAcquisitioR of a sensor/

sensor system can be fixed using the equation:

)( ,ActuatorDeploymentTrackingnAcquisitionAcquisitio tttvR .

The minimum detection range nAcquisitioR (coverage range) is the example above is

specified by:

TrackingTrackingnAcquisitionAcquisitio Rfp

NvRtvR

mmsmR

snAcquisitio 2,313,23

207,089,13

1

if the same detection probability of p = 0,7 is valid for this far area.

This was an example for vehicle speed of 50 km/h. Of course, it is possible tocalculate the equivalent values for other vehicle speeds. This is done in the intervalbetween 25 km/h and 50 km/h. The results are summarized in Figure 4.10.

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Figure 4.10. Time Scheme for deployment of warning signals or automaticdeceleration actuators.

It is visible that the maximum range is directly related to the vehicle speed. In theSAVE-U project it was decided to have an upper boundary at 40 km/h. At this speedand with the described conditions the maximum range will be in the order of 25 m.

4.6.4 Sensor specification

An efficient VRU protection system requires several elements from the sensors pointof view. Firstly, sensors must cover the field of view which is relevant to deal with amajority of situations. Secondly, they have to provide sufficient information to permitreliable VRU detection and differentiate them from other objects such as a tree,vehicle or roadside furniture. Thirdly, the VRU relative distance and velocity from thevehicle is compulsory to activate the protection systems correctly.

The sensor performance will determine whether object detection and recognition at agiven distance from the moving vehicle is feasible. However, the detection of humantargets by sensors is possible and has been demonstrated over the years inapplications ranging from surveillance radars to supermarket door openers and

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vehicle or building security detectors. In such applications a false detection does notrepresent a major concern. A missed detection by a door opener is not lifethreatening. In a pedestrian protection system, it may lead to act in a way that couldat least annoy the driver or in worst cases endanger life.

4.6.4.1 Radar sensors

Active sensors, such as the radar system used in SAVE-U, possess the followingspecific characteristics:

Radar systems can detect objects and measure range and dynamics in adirect way

Require less computing powers as they acquire a considerably lower amountof data,

More robust to bad weather conditions, not influenced by illumination condition Can work in harsh environment and then match automotive specifications Very easy to integrate on a car (invisible behind a bumper)

But the SAVE-U radar sensors also have some drawbacks: A low angular resolution, Wide variation in reflection caused by obstacles shape or material, Object classification difficult, Geometrical fading effects between sensor and target in a real measurement

environment (e. g. real road conditions).

The short range radar sensors used in this project will operate according to thefrequency modulated continuous wave (FMCW) principle. The basic idea behindFMCW is to transmit a RF signal showing linearly increasing instantaneousfrequency over time T. This frequency ramp is called slope, the resulting RF signalis called chirp. The signal propagates to the object, where it will be reflectedaccording the object RCS. The received RF signal is detected and down convertedusing the instantaneous transmit frequency. By doing so, the signal time of flight(delay tL) of a radar echo results in a constant frequency shift fb (beat frequency) ofthe received signal (called IF signal). The frequency shift is additively influenced bythe Doppler frequency shift fd generated by the radial relative target velocity. Theafter all frequency shift is df=fd - fL for an up going frequency ramp (up slope). After

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A/D-conversion of the IF signal, a spectral analysis (for example a FFT) is applied tothe samples of the received signal within the interval T. The detected peaks in eachspectrum represent the frequencies of the IF signals caused by the different targets.Therefore radar sensors are able to measure range and velocity in a direct way.

The radars used in this project measure runtime, power and Doppler frequency shiftof electromagnetic waves, emitting from the sensor and reflected back from objectsin the field of view. Runtime is a measure for the distance and Doppler frequencyshift for the velocity. These SAVE-U sensors cannot provide a direct anglemeasurement.

Radar measures only point targets (reflection centres) even on extended object.Vehicles, trees, traffic furniture�s, bicycles and human beings are detected. Streetand pavement are not seen, because of the low angle of incidence to the road andtherefore the lack of significant reflections.

If we consider the radar equation:

24321

)4()()(

RGGPP emitreceive ,

where R is the measured range and G1, G2 the antenna gains depending on thetarget angle (antenna diagram).

With the receive power and the formula above, an estimation of the Radar CrossSection (RCS) for each detected object could be calculated. RCS is used to classifybetween objects, pedestrians have a typical RCS between 0.01 m2 and 1 m2 for24 GHz radars while cars have values between 0.1 m2 and 1000 m2.

The general physical effect of a signal being erased by the radar wave (fading)causes in a fluctuation in the signal amplitude. The fading effect is geometrical, i. e. itdepends on the sensor and target height. The signal amplitude depends on thereflectivity of the road as well. According the fluctuation of the signal amplitude theclassification of objects is not possible in the worst case.

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Another criterion is the velocity. Pedestrians have a typical velocity of 2 m/s up to5 m/s, while bicycles can easily reach 10 m/s. One natural way for radar detectionand rough classification is to combine the RCS and velocity criteria.

4.6.4.2 Video sensors

Vision-based sensors are defined as passive sensors and have some real qualitiesfor VRU detection:

High spatial resolution at reasonable cost Visual information can be retrieved (such as lane markings localization, traffic

signs recognition, obstacle identification)

Unfortunately, vision sensors present also some disadvantages, which are: For high resolution sensors, a very heavy computing power is required Not well adapted to work in bad weather conditions Not adapted to work at night except for IR sensors

Single camera set-up is the basic optical arrangement (but stereo vision is possibleas well, refer section 1.3.2.2 in the annex). Some parameters of camera must beconsidered carefully: spatial resolution, view angle and dynamic range.

Spatial resolutionThe spatial resolution is concerned with the object detection. Spatial resolution isdecided by the resolution of camera. Higher resolution camera can produce finer andmore precise image thus improves the obstacle perceptibility. It is especiallyimportant for a detection of small obstacles in large distance. On the other hand,higher resolution image increases the computation time and cost which are bothcritical factor in the field of automotive implementation. One has to make a trade-offbetween the low and high camera resolutions.

Choosing a camera resolution means to answer to what is the minimum size of anobject to be detected and what is the minimum pixel number needed for a reliabledetection and classification.

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Given the physical size of obstacle at distances of 25 m and 35 m, the number ofimage pixels of the obstacle can be calculated with camera parameters. Forcalculation purpose we consider only pedestrian detection and classification withouttaking into account lighting or weather conditions.

In terms of resolution, the most critical axis is the horizontal one due to the smallwidth of a pedestrian. This one is then considered to evaluate camera specificationsand we state to detect 40 cm (vertically) on the horizontal axis and120 cm (horizontally) on the vertical axis.

For automotive application, video sensors present a maximum resolution of640 x 480 pixels. The sensor size is fixed to a ½� format 6.4 mm x 4.8 mm.

The height h and width w of the object projection on the sensor plane can becalculated:

fDWv

fDHh

and then object size in pixels are given by

8.4480

4.6640

vvp

hhp

(see results in the Table 5.3)

Focal length (mm) 25 20 15 10

D = 25 m hp

vp

40

120

32

96

24

72

16

48

D = 35 m hp

vp

29

86

23

69

17

51

11

34

Horizontal angle of view 14.6° 18.2° 24.1° 35.5°

Vertical angle of view 11.0° 13.7° 18.2° 27.0°

Table 4.3. Camera parameters.

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View angleThe minimum size of a patch of pixels which enables a good detection is very difficultto determine. It depends of lightings conditions, pedestrian clothing and also ofalgorithms used for detection and classification. But this size is a key factor to specifya video sensor. One has to be sure that this size does not implicate a too small angleof view. The value of the angle of view must insure the detection in advance ofpotential dangerous situations for VRU. For that goal, VRU have to enter the field ofview at a time which permits an early detection.

dc

dv

dc

dv

Figure 4.11. Configuration camera field of view.

If we consider the collision point (in red), the VRU and the vehicle reach this pointafter T second express by dv/vv = dc/vc. The minimum angle of view is then given by

)arctan(2)arctan(2vcv

dd v

c

v

which express that the angle is directly linked to the relative speed between VRU andvehicle.

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Vv (vehicle velocity)m/s

Vvru (VRU velocity)m/s

(minimum angle of view)Degree

16.7 (60 km/h) 6.9 (25 km/h) 44.9

1.0 (3.6 km/h) 6.813.9 (50 km/h) 6.9 (25 km/h) 52.8

1.0 (3.6 km/h) 8.211.1 (40 km/h) 6.9 (25 km/h) 63.7

1.0 (3.6 km/h) 10.3Table 4.4. Minimum camera coverage angle versus different vehicle and VRU

velocities.

The Table 5.4 gives an idea for the values of the angle of view. However, the choiceof the angle is always a trade-off between the minimum patch of pixels, the cameraresolution, the computing power available and the scenario requirements.

Video sensor intensity dynamicIn an automotive application, the sensor is really pushed to the limit. The variation ofillumination is huge: on sunny day very bright light could saturate the sensor, while atnight, images are taken only with the headlight illumination. The average illuminationis varying but also inside a single image very high variation of lights may occur due tobacklighting effects for example. The maximal intensity variation of an image, whichis acceptable, is given by the dynamic range of the sensor. For classic CCD sensors,the ratio between the lowest and the highest variation is limited up to 60dB, which istoo low for automotive application. CMOS sensors with logarithmic response preventsaturation of the image and permits contrast of more than 120 dB.

However, CMOS sensors show a lack in sensitivity, which make them blind in poorlevel of light. This is the reason why in the SAVE-U project, an infra-red camera willbe used especially at night. Recently the emergence of a new generation of infraredsensors � the micro bolometer technology � based on an infrared thermal detectionmechanism which is particularly suited to operate at ambient temperature hasopened the opportunity for achieving low cost infrared imaging systems for bothmilitary and commercial applications. In fact, Infrared detection offers largeadvantages in comparison to sensors working in visible spectrum. Obviously Infrared

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detection is not affected by poor conditions of light or bad weather conditions. TheSAVE-U project relies on a high performance amorphous silicon micro bolometer14 bit sensor which has been developed at CEA/LETI, particularly relevant toautomotive applications. In the footsteps of MEMS devices, micro bolometer sensorshave taken benefits from the latest silicon technology advances. Unique surfacemicromachining technique has been developed in order to release above a fullcustom CMOS readout circuit, very thin membranes made from amorphous siliconthat are very sensitive to infrared incoming radiations heating. One of the key point ofLETI micro bolometer technology has been to elect amorphous silicon material whichis strictly compatible with standard silicon processing. In fact, this basic option leadsto high yield monolithic arrangement fully compatible with commercially availableCMOS silicon wafers. This feature guaranties low cost attainment particularly suitedfor large market diffusion.

4.7 Sum up according to analyzed actuators and sensors

The above chapters 3 and 4 presented possible implementation of actuators andsensors as a SAVE-U system included modern, best in each class systems availableon a market or in development. Their efficient function in defined situations dependson many factors. In the concept of the project a common work of all components withutilization of information delivered by platform sensors are foreseen. The function ofeach component of the system can not be treated as isolated. Each componentshould be optimally integrated in such a way, that its best performance is used andthe actuators and sensors are acting in a mutual co-operation. The accuracy ofdelivered data by each sensor is additionally very important by consideration ofparticular traffic situation.

The sensor physical properties determine accuracy of the delivered data andchanges in time and space. It would be of great advantage to obtain how theaccuracy of the measured data and the interpretation of each parameter haveinfluences on the efficiency of the whole system as a complex system consisting ofdriver, vehicle, pedestrian and environment.

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It is well-known, that these interactions � however easily to suppose qualitatively -are very difficult to obtain quantitatively. The practical evaluation of the systemperformance seems to be the more reasonable way.

They are a lot of parameters and factors, which however important for effectiveoperation of the system, are not possible to measure and therefore can not wholly betaken into account for the elaboration of algorithms. Such factors are: complexity ofscenario (visibility, lighting), state of road surface, personal condition of the drivers(tired, healthy, old, young, gender etc.) and state of the vehicle. These factors arenot stable and can change also in a very short time.

The estimation of possible influence these factors have on the quality of function ofthe system can be made approximately and subjectively only.

In the two tables below an estimation attempt for possible interactions and theirimportance for the drivers and the protection potential for pedestrian was made. Itsummarizes the considerations above: in the first one (Table 4.5) the possible impactfor the proper function of each actuator, in the second one (Table 4.6) the impact ofmeasurement accuracy of parameters for different kinds of sensors.

Actuator

TrafficUserVehicleDriver + + *) 0 0 0 0 + 0 + +Pedestrian/VRU + 0 + + + + 0 + 0 0

Table 4.5. Evaluation of influence of actuator on driver and pedestrian,respectively. Legend: �+� = helpful; �0� = not directly helpful; *) = if a warning

can be applied early enough to the driver.

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TrajectoryMeasurementSensor

Technology x Y Vx Vy

Objectclassification

capability

Objectgeometry

measurementRadar ++ + ++ 0 + +Video

- mono- stereo

+++

+++

00

00

++++

++++

Laser ++ ++ 0 0 0 ++Table 4.6. Evaluation of the sensor measurement capabilities (without

tracking).

In this place it is necessary to explain the difference of terms like measurement andestimation for the reader. The meaning of measurement in the Table 4.6 is that theseparameters can be observed directly by recognising of physical effects (like time-of-flight or Doppler frequency) by the sensor. In contrast to measurement the parameterestimation can provide additional values for not measured parameters. But it is wellknown from the information theory by Shannon that the estimation can not increasethe information value (entropy) of the measurement. Estimation can only help to findan approximation for not measured values by using a model. Usually this is the taskfor tracking algorithms.

The Table 4.6 shows that the radar is good at position and dynamic measurement,video is good at position measurement and classification. Consequently, thecombination (fusion) of both seems to be a very suitable solution for the VRUdetection problem and for enhancing VRU�s safety.

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5. Conclusion

This document is the Deliverable D 6 entitled �Strategies in Terms of PedestrianProtection� of the EC-funded project SAVE-U. It contains the outcome ofworkpackage WP3.

The description starts with a survey on published information about the state of theart of protection systems for vulnerable road users (see D6 Annex). The survey isbased on published conference papers, patents and presentations from the internet.This bibliography provides an overview of the wide range of these kinds of actuatorsystems (like active hoods, active bumpers, night vision systems, driver warning,pedestrian warning, automatic braking, etc.). The state of the art bibliography isfollowed by a detailed technical description of the full spectrum of actuators currentlyunder investigation. This is an introduction to understand the technology and theconsequences for deployment. In addition to this �on-board-systems� hints topossibilities in terms of road constructing to avoid accidents will be presented.

The technical description is the base for a serious evaluation of actuator methods forVRU protection. There were several criteria developed for evaluating, namely:

Reversible/ Irreversible/ No Deployment Passive/ Crash-active/ preventive Methods Protection of VRU or occupants Protection potential from accident statistic point of view Avoidance or reduction of primary impact Avoidance or reduction of secondary/ tertiary impact

Actuators which can be triggered in a reversible way seem to be the only realisticway to enhance VRU�s safety using current sensors. Irreversible actuators need100% fault safe sensors (with performance like current crash-sensors for airbagdeployment). If they need a pre-trigger, than none of today�s sensors will be able tocontrol these actuators adequately.

All measures which need no deployment are pure-passive methods. Of course, theyare useful, but not investigated in the SAVE-U project.

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The discrimination between passive, crash-active and preventive actuators describesthe deployment time before collision: Pure-passive methods don�t requiredeployment; crash-active methods can provide protection potential just as the crashoccurs (contact moment). But the preventive deployable actuators can be triggeredsome milliseconds or seconds before the contact occurs. So, they have more time tomitigate the collision severity and therefore they were selected for the SAVE-Uproject.

The criteria of VRU or occupant protection indicate in a very clear manner, whichcollision partner can be protected by this actuator.

The fourth criterion deals with an accident statistic consideration. If the accidentstatistics shows that this actuator can protect VRUs than this is marked in thiscriterion.

The reduction of primary and secondary/ tertiary impact is an additional item. Most ofthe actuators discussed in the scientific world reduce the primary impact (say:Collision VRU versus vehicle) only. The secondary and tertiary impact (say: VRUversus road surface, VRU versus second vehicle, respectively) shows also very highinjury levels in the accidents. Therefore the goal must be to reduce both, primary andsecondary/ tertiary impacts for most effective VRU protection approach.

Based on these conclusions it was decided in the current project stage to usepreventive system actuators for SAVE-U, namely automatic soft braking and driverwarning concepts. The number of false alarms must be very low. This can beguaranteed by deploying the signal only in the case that an unavoidable collision ispredicted.

More technical details regarding sensor performance and system performance will besummarized in Deliverable D7 outcome of work package WP 4.

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6. References

[1] US 4 518 183:�extendable safety impact bags for vehicles�date of patent: May 21, 1985

[2] DE 24 38 828 C2:�Stoßfänger für schwere Fahrzeuge (bumper for heavy vehicles)�date of patent: May 07, 1987

[3] DE 44 29 755 A1:�Ausfahrbare Stoßstange für Kraftfahrzeuge zur Minderung undVermeidung von Auffahrunfällen (extendable bumper for motor vehiclesfor decrease and avoidance of bumper-to-bumper collisions)�date of disclosure: Feb. 29, 1996

[4] DE 195 14 191 C2:�Sicherheitssystem für Fahrzeuge (security system for vehicles)�date of patent: July 09, 1998

[5] DE 197 50 299 A1:�Fahrzeug (vehicle)�date of disclosure: may 20, 1999

[6] DE 198 18 586 C1:�Schutzvorrichtung für ein Kraftfahrzeug (protection device for motorvehicles)�date of patent: September 30, 1999

[7] DE 198 06 039 A1:�Erweiterung der Knautschzone bei PKW bzw. KFZ (extension ofdeformation zone at motor vehicles)�date of disclosure: August 19, 1999

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[8] DE 199 05 784 A1:�Kraftfahrzeug mit einer Aufprallschutzvorrichtung (vehicle with crashprotection device)�date of disclosure: September 9, 1999

[9] EP 0 894 677 A1:�Agencement d�une poutre de pare-chocs dans un véhicule automobile(hydraulic bumper bar for motor vehicles)�date of disclosure: February 3, 1999

[ABOWD] ABOWD Peter � Visteon �Head-Up Display�

[ATZ01] �Automobiltechnische Zeitschrift (ATZ)�9/2001, page 780ff.

[BEE02] Benno Beesten, Stefan Hagen, Matthias Rabe:�Out-of-position simulation � possibilities and limitations withconventional methods�Symposium Airbag 2002, Karlsruhe, 02.-04.12.2002.

[BIN] Bin Ran, Henry X. Liu:�A Framework for the Development of a Proactive Exterior AirbagSystem�

[BOS02] Robert Bosch GmbH �Kraftfahrtechnisches Taschenbuch� Edition 24, ISBN3-528-13876-9, 2002.

[BÜT02] Büttner, C.:�Sichtverbesserung bei Nachtfahrten, Infrarottechnologie für dieFahrzeuganwendung�Raytheon GmbH, 2002

[CERTIN] CERTIN Laurent / Florence NATHAN - PSA Peugeot Citroën Night Vision Human / System Interface

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[DEK02] F. A. Berg; M. Egelhaaf; J. Bakker, H. Bürkle, R. Herrmann, J.Scheerer:�Pedestrian Protection In Europe - The Potential of Car Design andImpact Testing�DEKRA Automobil GmbH, Unfallforschung, Stuttgart; DaimlerChryslerAG, Unfallforschung, Sindelfingen, 2002.

[DUMAS9] Transport In The Urban Environment.�The Institution of Highways and Transportation�June 1997.

[DUMAS10] �DUMAS - Hastighedsplan for Gladsaxe kommune.�Cowi, 1996.

[DUMAS11] Kenneth Kjemtrup and Lene Herrstedt :"Speed Management and Traffic Calming in Urban Areas in Europe: AHistorical View".The Danish Road Directorate, 1992.

[DUMAS12] �Byernes Trafikarealer�Volume 0-10 (Danish Road Standards for geometric design of urbanareas � Recommended guidelines.) The Danish Road Directorate,1991. Volume 0, 4, 7 and 10 in English.

[DUMAS13] �Towards safer roads.�Publication from the Transport Research Centre (AVV) of the Ministryof Transport and Public Works, Rotterdam, the Netherlands.

[EDW94] Edworthy, J; Meredith, C.S.:Cognitive psychology and the design of alarm sounds.Medical Engineering and Physics, Band 16 (1994), Heft 6, 445-449.

[FRA] U. Franke, D. Gavrila, S. Gorzig, F. Paetzold, C. Wohler:�Autonomous Driving approaches Downtown�Daimler-Benz Research.

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[FIR99] �F.I.R.S.T. � Fully Integrated Road Safety Technology�BMW AG Presse- und Öffentlichkeitsarbeit, 1999.

[GAV01] Gavrila, Dariu M.:�Sensor-based pedestrian protection�IEEE Intelligent Systems, vol. 16, no. 6, pp. 77-81, 2001.

[GET95] Getty, Fl. J., Swets, J. A., Pickett, R. M. and Gonthier, D.:�System operator response to warnings of danger: a laboratoryinvestigation of the effects of the predictive value of a warning onhuman response time�Journal of Experimental Psychology: Applied, 1995, 1(1).

[GDV01] �Sicherung des Verkehrs auf Straßen �SVS- - Auswertung vonStraßenunfällen Teil 2 � Maßnahmen gegen Unfallhäufungen�

Gesamtverband der Deutschen Versicherungswirtschaft (GDV), Institutfür Straßenverkehr Köln (ISK), Forschungsgesellschaft für Straßen- undVerkehrswesen Köln, Polizei-Führungsakademie Münster, Februar2001.

[HAL01] Rikard Fredriksson Yngve Håland:�EVALUATION OF A NEW PEDESTRIAN HEAD INJURYPROTECTION SYSTEM WITH A SENSOR IN THE BUMPER ANDLIFTING OF THE BONNET�S REAR PART�Autoliv Research, Sweden Jikuang Yang Chalmers University ofTechnology, Sweden Paper number: 131, 2001. www.autoliv.com,11/2002

[KOP98] Kopf, M.:�Warnungen und ihre Auswirkungen auf den Fahrer.�BMW AG, EW-11, München, 1998.

[KOV99] Kovanda, Jan; Riva, Riccardo: �Vehicle-Human Interaction� Edizioni Spiegel, Milano, Italy, ISBN 88-7660-104-X, 1999.

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[LIU02] Liu, X., Oh, J., and Recker, W.: �Adaptive Signal Control with On-line Performance Measure�

Transportation Research Board 81th Annual Meeting, Washington DC,January 2002.

[MAZ99] �Mazda Develops Advanced Safety Vehicle Mazda ASV-2�Mazda, October 7,1999

[MEN02] Mende, Ralph; Rohling, Hermann: �New Automotive Applications for Smart Radar Systems�

German Radar Symposium, Bonn/ Germany, September 3-5, 2002.

[MIT00] �MMC announces Mitsubishi ASV-2�Mitsubishi, June 19, 2000.

[NIL02] Takehiko Suzuki, NILIM:�TEST OF LASER-TYPE PEDESTRIAN DETECTORS IN SNOWYAND COLD AREAS�(Presented by Mr. Norio Kamagami, Ishikawajima Harima HeavyIndustries, Japan)ITS World Congress, Chicago, 2002.

[NIS03] �Nissan Offers Pre-crash Seatbelt Technology�http://www.nissan-global.com/EN/STORY/0,1299,SI9-CH179-LO3-TI740-CI571-IFY-MC109,00.html

[ORI98] �Study of the efficiency of infrastructural measures for pedestrianprotection � final report � global study of France and U.K. sites�

Orientations, L�ingeniere des deplacements, Jan 1998.

[ÖST02] �Österreichisches Verkehrssicherheitsprogramm 2002-2010 �Strategien für mehr Sicherheit auf der Straße�Bundesministerium für Verkehr Innovationen und Technologie, WienAustria, 2002.

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[PRIT97] �Pilot non-conformance to alerting system commands�1997 IEEE International Conference on Systems, Man, andCybernetics. Computational Cybernetics and Simulation,12-15 Oct. 1997, Orlando, FL, USA, Band 3 (1997), 2125-2130.

[PRO01] �Programm für mehr Sicherheit im Straßenverkehr�Bundesministerium für Verkehr-, Bau- und Wohnungswesen, 2001.

[SAV03] Dr. Dariu Gavrila, Philippe Marchal, Dr. Marc-Michael Meinecke:�SAVE-U - Deliverable D1A: Vulnerable Road User Scenario Analysis.�EU-Project SAVE-U, 21.02.2003.

[STE2001] Stevens, A.: Information form response relevant to warnings. TRL Limited, Crowthorne, Berkshire, GB, 2001.

[USH94] Usher, D.M. �The alarm matrix. In N. Stanton (Ed.), Human Factors in Alarm Design� Taylor & Francis, London, 1994, 139-146.

[VIENOT] Françoise VIENOT�Photobiliology laboratory of �Museum National d�Histoire Naturelle�

Mesopic Vision

[WEB00] Pia Weber, Christian Strube:�Fußgängerschutz, Lösungsansätze für fußgängerschutzoptimierteFahrzeuge�Volkswagen AG, 2000

[WHI01] �White Paper � European transport policy for 2010: time to decide�Office of the official publications of the European communities,Luxembourg, ISBN 92-894-0341-1, 2001.

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7. List of Figures

Figure 3.1. Example of collision pedestrian versus vehicle. ..................................... 11Figure 3.2. Overview about passive and active methods for protection of unprotected

road users. ........................................................................................................ 14Figure 3.3. Deployment of actuators: Phase 0 (VRU invisible)................................. 18Figure 3.4. Deployment of actuators: Phase 1 (acquisition phase) .......................... 18Figure 3.5. Deployment of actuators: Phase 2 (tracking phase)............................... 19Figure 3.6. Deployment of actuators: Phase 3 (deployment phase)......................... 20Figure 3.7. Deployment of actuators: Phase 4 (contact)........................................... 20Figure 3.8. Example of a conventional braking system. ........................................... 23Figure 3.9. Example of a brake booster.................................................................... 24Figure 3.10. Components of a brake system............................................................ 25Figure 3.11. Electro-hydraulically Brake (EHB). ....................................................... 27Figure 3.12. Block diagram of an electro-hydraulic braking system [BOS02]. .......... 28Figure 3.13. Comparison between a conventional brake system and an electro-

hydraulic brake system (EHB). .......................................................................... 29Figure 3.14. Electro-mechanical brake (EMB).......................................................... 32Figure 3.15. Comparison between conventional brake system and electro-

mechanical brake system (EMB)....................................................................... 33Figure 3.16. Simulated effects of different kind of braking........................................ 35Figure 3.17. Airbag deployment. .............................................................................. 37Figure 3.18. Passenger airbag with hybrid inflator

(http://www.autoliv.com/appl_alv/Autoliv.nsf/pages/library_illustrations) ........... 38Figure 3.19. Airbag inflation device with solid propellant

(http://www.howstuffworks.com/airbag1.htm).................................................... 38Figure 3.20. Airbag Vents......................................................................................... 39Figure 3.21. Piloted vents (Delphi) ........................................................................... 40Figure 3.22. Configuration of discriminating and saving sensors (adapted from

Struble).............................................................................................................. 41Figure 3.23. Crash sensor (http://www.lemurzone.com/airbag/crash.htm) ............... 41Figure 3.25. Configuration of proactive exterior airbag systems............................... 42Figure 3.26. Closed end exhausted airbag system................................................... 43Figure 3.27. Windshield airbag................................................................................. 44

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Figure 3.28. Intrusion measurement on an adult dummy head. ............................... 46Figure 3.29. Bonnet head form tests performed at BASt in Germany, 40 km/h impact

speed (Zellmer and Glaser, 1994)..................................................................... 48Figure 3.30. Bonnet with protection system in activated (lifted) position. ................. 49Figure 3.31. Example of a pneumatic muscle........................................................... 51Figure 3.32. Contraction of a pneumatic muscle for hood lifting............................... 51Figure 3.33. Position of sensors in bumper (1: contact sensor, 2: accelerometers). 53Figure 3.34. Sensor tests at 25 km/h........................................................................ 54Figure 3.35. Head-impact results at 40 km/h (25 mph) using the proposed European

test limit with a standard hood and with an active hood from Autoliv................. 55Figure 3.36. Crash test in 40 km/h with a pedestrian dummy and an active bonnet. 57Figure 3.37. Example of an active bumper system [6].............................................. 58Figure 3.38. Impact of a 3-year old child (P3) and 50%-male dummy (HII) on a hood

[WEB00] ............................................................................................................ 59Figure 3.39. Cross section of inflatable bumper [6]. Legend: 1: vehicle�s contour,

2: support, 3: guiding, 4: airbag, 5: gas generator, 6: pressure measuringinstrument. ........................................................................................................ 62

Figure 3.40. Inflatable units at front and rear end [6]. Legend: 2: bumpers, 4: airbags........................................................................................................................... 63

Figure 3.41. Scheme of scanning and deployed active bumper system [7]. Legend:1: radar receiver, 2: wire, 3: radar transmitter, 4: computer, 5: speed sensor,6: obstacle,7: frame, 9: pyrotechnical mechanism, 10: deformation mechanism........................................................................................................................... 63

Figure 3.42. Reaction propulsion drive for active bumpers [4]. Legend: 7: support ,9: cartridge, 11: charge, 13: rod, 15: support, 17: nozzle, 19: stroke. ............... 64

Figure 3.43. Hydraulic active bumper [9] .................................................................. 65Figure 3.44. Electrical release unit of a hydraulic rod [9]. Legend: 16: housing,

20: jack, 22: body, 24: stem, 30: package, 56: blocking, 57: broach, 58: block,60: flange, 62: guiding, 63: annular reinforcement, 66: wheel, 68: rod, 70: rod,74: positioning stop, 76: complementary stop. .................................................. 66

Figure 3.45. Rain sensor: Localisation of transmitter LED and receiver diode. ........ 69Figure 3.46. Principle of rain detection by reflection measurement techniques on the

windshield.......................................................................................................... 70Figure 3.47. Detailed structure of a rain sensor........................................................ 71Figure 3.48. Even water-based adhesive drips off the lotus leave (photo: Prof.

Barthlott, University of Bonn)............................................................................. 72Figure 3.49. Active night vision with IR-headlamps (photo: HELLA)......................... 73

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Figure 3.50. Comparison of direct and IR vision (Valeo) .......................................... 75Figure 3.51. Infrared camera (Raytheon) ................................................................. 76Figure 3.52. Two examples of head-up displays. Left: IR camera image projected,

Right: Navigation data, speed information and object information projected..... 76Figure 3.53. IR filter in headlamp (Valeo) ................................................................. 77Figure 3.54. Example for driver warning system. ..................................................... 78Figure 3.55. Reversible seat-belt pre-tensioner........................................................ 86Figure 3.56. Reversible seat-belt retractor and its force diagram. ............................ 87Figure 3.57. Severity index of different types of measures....................................... 94Figure 3.58. Severity index of different area types. .................................................. 95Figure 3.59. Siteco lighting engineering. .................................................................. 97Figure 3.60. Invisibility of VRU at the tunnel exit ...................................................... 98Figure 3.61. Tunnel exit - View from inside the car................................................... 98Figure 3.62. Cars blocking sight on pedestrian ........................................................ 99Figure 3.63. View from inside the car ..................................................................... 100Figure 3.64. Single-side illuminated road ............................................................... 101Figure 3.65. Children in front of a school building, far-off pedestrian crossing ....... 102Figure 4.1. Collision speed versus braking duration. Initial speed 50 km/h (blue lines),

40 km/h (green lines). Deceleration a = -1 m/s2 and a = -2 m/s2, respectively.108Figure 4.2. Reduction of collision speed square vCollision

2 during the contact versusbraking duration. Initial speed 50 km/h (blue lines), 40 km/h (green lines).Deceleration a = -1 m/s2 and a = -2 m/s2 respectively..................................... 109

Figure 4.3. Cumulative frequency of MAIS2+ casualties versus collision speed. ... 110Figure 4.4. Measurement accuracy of a single measurement in the x-y-plane....... 116Figure 4.5. Measurement accuracy of a single measurement in x-direction (y = 0 m).

........................................................................................................................ 117Figure 4.6. Measured position assuming detection probability of 70 %. ................. 118Figure 4.7. Measured position (blue) and tracked position (red) assuming detection

probability of 70 %........................................................................................... 120Figure 4.8. Accuracy of a single measurement (blue) and theoretical track accuracy

(red) assuming detection probability of 100 %. ............................................... 121Figure 4.9. Maximum range versus braking acceleration (a = -1 m/s2 � -9,81 m/s2).

........................................................................................................................ 122Figure 4.10. Time Scheme for deployment of warning signals or automatic

deceleration actuators. .................................................................................... 125Figure 4.11. Configuration camera field of view. .................................................... 130

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8. List of Tables

Table 3.1. Examples of reversible and non-reversible protection systems. .............. 16Table 3.2. Consequences of reversible and non-reversible methods. ...................... 17Table 3.3. Reaction time (measurement results). ..................................................... 52Table 3.4. Results from head form tests at 50 km/h, comparing the active bonnet with

the standard bonnet. ......................................................................................... 55Table 3.5. Possible acoustic reactions to alert and dangerous situations................. 84Table 3.6: Possible visual reactions to alert and dangerous situations..................... 85Table 3.7. Simplified example of the Danish road and speed classification system. 91Table 3.8. Overview of the analysed sites from France and UK allocated to area

types and infrastructural measures ................................................................... 92Table 3.9. Reduction of pedestrian victims of the single area types and due to the

single infrastructural measures.......................................................................... 94Table 3.10. Results of the FYRR-calculation of the single area types and of to the

single infrastructural measures.......................................................................... 95Table 4.1. Overview about protection systems and their protection potential. Legend:

�+�: positive evaluation level, �0�: neutral evaluation level, �-�: negative evaluationlevel. *) valid for reversible variant only. .......................................................... 106

Table 4.2. Hints of system specifications for different VRU protection actuators(legend: = as high as possible (>>99,9 %); = as low as possible (<<0,1 %))......................................................................................................................... 113

Table 4.3. Camera parameters............................................................................... 129Table 4.4. Minimum camera coverage angle versus different vehicle and VRU

velocities. ........................................................................................................ 131Table 4.5. Evaluation of influence of actuator on driver and pedestrian, respectively.

Legend: �+� = helpful; �0� = not directly helpful; *) = if a warning can be appliedearly enough to the driver................................................................................ 133

Table 4.6. Evaluation of the sensor measurement capabilities (without tracking). . 134