Ray et al 1

1. Assistant Professor of Civil Engineering, Center for Computer Aided Design,University of Iowa, Iowa City, IA 52242. 319-335-3383. mhray@ccad.uiowa.edu.

2. Mechanical Engineer, Safety Design Division, Federal Highway Administration,2800 Georgetown Pike, McLean, VA 22101 703-285-2508Martin.Hargrave@fhwa.dot.gov

3. Provost, Worcester Polytechnic University, 100 Institute Road, Worcester, MA01609-2280 508-831-5222, jfc@wpi.edu

4. Graduate Research Assistant, Center for Computer Aided Design, University ofIowa, Iowa City, IA 52242. hiranmay@icaen.uiowa.edu.

SIDE IMPACT CRASH TEST AND EVALUATION CRITERIA FOR ROADSIDE SAFETY HARDWARE

M. H. RAY,1 M. W. HARGRAVE,2 J. F. CARNEY III3 AND K. HIRANMAYEE4

Abstract Reducing the severity of side impact collisions has been an emerging area of researchduring the past decade by a variety of organizations and research communities. Themotor vehicle manufacturing and regulatory communities in both the United States,Europe and many other countries have developed dynamic side impact test andevaluation criteria to reduce the severity of vehicle-to-vehicle side impact collisions. Similarly, the international research community has developed test procedures forperforming impacts into poles, one of the most severe types of side impact collisions. This paper presents preliminary side impact test and evaluation procedures for roadsidesafety hardware like guardrails, guardrail terminals, luminaire supports, utility polesand signs. The purpose of this paper is to summarize recommendations for performingroadside hardware side impact crash tests, describe the results of several side impactroadside hardware crash tests, compare the proposed test and evaluation procedures toother major side impact test and evaluation procedures, and discuss areas requiringfurther research.

INTRODUCTIONEach year about 225,000 people are involved in side-impact collisions with roadside objects like treesutility poles and guardrail terminals. It has been estimated that the societal cost of side impact collisionswith fixed roadside objects exceeds three billion dollars annually.(1) One in three vehicle occupantsinvolved in side impacts with roadside objects are injured and one in one hundred is fatally injured. Sideimpacts with roadside objects are a significant cause of human trauma and improved roadside hardwaredesign can help to alleviate that suffering. Developing roadside hardware with better side impactperformance is an emerging factor in improving roadside safety in the next decade but before roadsidehardware can be designed for side impacts, the roadside safety community must develop a consensus onhow side impact crash tests should be performed and what constitutes successful performance.

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Figure 1. Orientation for sideimpact crash tests.

The purpose of side impact crash tests is to assess the risk ofinjury to vehicle occupants in the event of a side impact crash andto develop techniques for minimizing this risk. Many agenciesand research organizations have recommended a variety ofmethods of performing and evaluating side impact crash tests. Each group has specific goals in proposing side impact test andevaluation criteria: the motor vehicle manufacturing communityseeks to improve the performance of vehicles, the biomechanicsresearch community seeks to implement more effective occupantprotection strategies, and the roadside safety research communityseeks to develop roadside safety hardware that performs well inside impact crashes. Ultimately all these groups are seeking toreduce the risk to vehicle occupants by improving the part of thevehicle-occupant-roadway system for which they haveresponsibility.

Often research communities develop procedures and evaluationcriteria in isolation from each other leading to difficulty in exchanging, interpreting, or using information. Ensuring that procedures and evaluation criteria are consistent with other disciplines wherever possiblecan greatly improve the quality and quantity of information exchange and thereby help researchers anddevelopers to find solutions more quickly. The purposes of this paper are to (1) present recommendationsfor performing side impact crash tests of roadside hardware, (2) describe the experience to-date in usingthe recommendations, (3) examine side impact test and evaluation criteria from the perspective ofharmonizing roadside safety standards with the other existing standards wherever possible and (4) toidentify areas needing additional research.

Figure 1 shows definitions for a variety of orientation angles that will be used throughout this paper. Theimpact angle ö is the angle between the forward direction of the target device and the forward direction ofthe impacting device. Both the target device and the impacting device can have a velocity vector that isnot coincident with the forward direction of the device. This angle is called the side-slip angle, Ù. Theside-slip angle for the impactor is denoted Ùi and for the target device is denoted as Ùt .

ROADSIDE HARDWARE SIDE IMPACT TEST AND EVALUATION CRITERIABackgroundNarrow objects subject the side of a vehicle to highly concentrated loadings that are difficult to resistwithout extensive vehicle deformation. An investigation of the Fatal Accident Reporting System (FARS)and National Accident Sampling System (NASS) showed that narrow objects, like the luminare supportshown in Figure 2, accounted for 60 percent of the side impact fixed-roadside object accidents and that 80percent of the fatalities in side impact accidents involved narrow fixed roadside objects like trees andutility poles.(1)

The roadside safety hardware community has recognized the severity and importance of side impactaccidents for many years. While 60 percent of all side impacts involve vehicles striking each other, nearly40 percent involve single vehicles striking fixed objects like trees, utility poles, light poles and guardrailterminals.(1) The first side impact crash test of a roadside safety feature was performed in the UnitedKingdom in 1969 when a small car was directed laterally across a wetted pavement into a luminaresupport.(2) In the United States the first side impact crash tests of roadside features were performed byButh, Olson and Samuelson at the Texas Transportation Institute for the Federal HighwayAdministration (FHWA) in the mid 1970's.(3) Two 45-km/hr, 90-degree impacts were performed toassess the breakaway performance of 9-m tall slipbase luminaires.(4) These early researchers recognizedthe potential severity of side impacts with narrow poles but they also discovered that performing and

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Figure 2. Result of a 50 km/hr impact of an 820-kgvehicle with a slipbase luminaire support.

Vehicle Type: NCHRP 820CTest Inertia 820 kgDummy mass 75 kgMaximum Ballast 50 kgGross Static 915 kgEngine Location FrontDrive Axle Location FrontNumber of doors Two

Test ConditionsLateral Velocity 50 km/hr or 60 km/hrLongitudinal Velocity 0 km/hrImpact Angle, ö 90 degreesYaw Angle, Ùi 0 degrees/secImpact Point Center of driver-side door

Dummy PositionDummy Type Part 572 F (SID)Position Impact side (driver side)Seat Horizontal Position Maximum rearwardSeat Back Position Normal upright Restraints All available restraints

Table 1. Recommended Test Conditions for RoadsideHardware Side Impact Crash Test.

evaluating such impacts was verychallenging.

The difficulty in performing these testsresulted in very little practical research aimedat improving the performance of roadsidehardware in side impacts until the mid1980's. The FHWA began the developmentof a state-of-the-art roadside hardware testfacility, the Federal Outdoor ImpactLaboratory (FOIL), at its McLean, Virginia researchfacility in the early 1980's. FHWAresearchers were aware of the research beingperformed by NHTSA in the area of sideimpact crash testing so they included thecapability to perform side impacts whendesigning the FOIL and performed a series offull-scale side impacts into luminaresupports.(4)

In 1988 the FHWA sponsored research to develop recommendations for performing full-scale side impactcrash tests of roadside safety hardware like guardrails, guardrail terminals, utility poles and luminaresupports. The recommendations were published in an FHWA report and they were also included asAppendix G in NCHRP Report 350, the test and evaluation procedures used by the roadside safetycommunity for all other types of full-scale crash tests.(5)(6) This paper summarizes and providescommentary on those recommendations.

RecommendationsThree basic principles guided the selection ofthe test and evaluation conditions for sideimpact crash testing of roadside objectssummarized in Tables 1 and 2. Roadsideobject side impact test and evaluationprocedures should:

C Be relevant to real-world roadsideobject side impacts,

C Conform wherever possible toexisting roadside safety hardwaretest and evaluation criteria (e.g.,NCHRP Report 350),

C Conform wherever possible toexisting side impact test andevaluation procedures (e.g.,NHTSA’s FMVSS 214, the EU sideimpact directive, and ISO standards) and

C Be repeatable.

Table 1 summarizes the impact conditionsand Table 2 summarizes the evaluation

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criteria recommended for side impact roadside object crash tests.

Crash test impact conditions should be relevant to the types of collisions that occur in the field. There aretwo basic approaches to selecting field relevant test conditions: the practical-worst-case approach and theaverage-condition approach. While NHTSA has generally adopted test conditions for typical (e.g., theaverage) impact conditions, the roadside safety community has traditionally used a practical worst casephilosophy. With this approach, the test conditions are selected, while not necessarily the most severe, aremore demanding than the average impact. For example, 90 percent of fixed roadside object side impactsoccur at a lateral velocity of 50 km/hr or less and nearly all such accidents occur at velocities of less than60 km/hr.(7) An impact velocity of 50 km/hr represents the 90th percentile impact velocity and 60 km/hrrepresents essentially the 100th percentile of side impact fixed roadside object impact velocities. The 50km/hr and 60 km/hr impact speeds recommended in Table 1, therefore, do represent two field-relevantpractical worst case scenarios.

Of equal importance is the expected harm in side impact collisions. Roughly half of severe occupantinjuries (e.g., AIS>3) occur when the total change in velocity is less than 50 km/hr and almost two thirdsof moderate and severe injuries (e.g., AIS>2) occur at velocities below 50 km/hr.(8) The basic 50 km/hrimpact velocity represents a reasonable worst case test condition in terms of expected impact speeds aswell as expected harm that is relevant to the way such collisions occur in the field. The higher 60 km/hroptional impact velocity was included to provide a test condition that represented even the most extremeside impact events. Obtaining good side impact performance at the higher 60 km/hr impact velocity,however, is expected to be significantly more difficult to achieve than at the 50 km/hr impact velocity.

Roadside hardware crash tests have been performed in the United States for over 30 years so there is aconsiderable body of expertise on performing full-scale tests. NCHRP Report 350 constitutes the latestfull-scale crash test and evaluation procedures used in the roadside safety research community.(6) Conforming where ever possible to current crash test recommendations in Report 350 was anotherimportant consideration when developing side impact test and evaluation recommendations. The vehicleselected as the test vehicle is the same 820-kg small passenger car that has been widely used in roadsidehardware crash testing for the past 15 years. Other aspects of testing like the instrumentation needs anddata acquisition specifications were taken directly from industry-wide guidelines like SAE J211 that arealso recommended in Report 350.(9)

While every effort was made to conform to Report 350 where possible, there are several areas whereReport 350 recommendations were not followed. For example, Report 350 discourages the use ofanthropometric test devices (ATD) because roadside hardware impacts are much more complex than thetypical unidirectional vehicle crashworthiness tests. Report 350 recommends the traditional flail spaceapproach instead and suggests that ATD only be used for ballast reasons. While the approach in Report350 may be a valid assessment of the use of dummies in redirectional crash tests, it did not correspond tothe situation in side impact crash tests. Instead the NHTSA approach of assessing performance based onthe response of the ATD was adopted. The reasons for this will be further explained in a later section.

Like the roadside safety research community, the vehicle crashworthiness research community hasdeveloped a great deal of expertise in performing and evaluating full-scale crash tests. The roadsidehardware side impact recommendations took advantage of this experience whenever possible byconforming to current NHTSA crash test procedures like FMVSS 214.(6) The ATD recommended foruse in roadside hardware side impact crash tests is the same test device specified by NHTSA for use inFMVSS 214 tests, the so-called side impact dummy (SID). The SID used in FMVSS 214 wasrecommended for use in roadside hardware side impact tests so that the evaluation parameters areidentical to FMVSS 214 requirements. Underlying this recommendation is a presumption that ATD,though they are far from perfect, are the best human surrogates for full-scale testing. One of the basic

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Figure 3. Side impact collision of a mid-size passengercar and a breakaway cable terminal in Iowa.

assumptions in developing roadside hardware side impact recommendations was that it is better to linkroadside hardware evaluation parameters directly to the biomechanics and injury tolerance researchperformed by NHTSA and the automotive industry rather than to try and develop independent correlationsto occupant injury. Other specifications in FMVSS 214 were adopted as-is into the roadside hardwareside impact test procedures including the positioning of the dummy, the location of the front seat, and theinstrumentation requirements.

Test conditions, though easily specified, can prove to be very challenging to implement in an actual crashtest. Vehicles in actual side impacts often experience complex motions including yaw rotations, rollingand pitching. To replicate such motions in a test would be very difficult and even if such motions wereachieved they may not be repeatable. The full-broadside impact orientation (e.g., ö=90o and Ùi=0o) wasrecommended for the following reasons:

C Mounting the vehicle at orientations other than 90o would be experimentally difficult and maynot be repeatable,

C Full broadside collisions (e.g., between 75o and 105o ) represent about 30 percent of all sideimpact with fixed objects, and

C Full broadside impacts make the use of ATD more legitimate.

The following sections describe particular aspects of the recommended roadside object side impact testprocedures.

Test ArticleAccident data indicate that side impacts arenot hazardous when the struck object is broadtherefore impacts where a vehicle slidessideways into the middle of a guardrail,median barrier or bridge rail are not likely tocause serious injury. Narrow objects, on theother hand, account 60 percent of thecollisions and 80 percent of the side impactfatalities.(1) Figure 3 shows a typical sideimpact accident involving a breakaway cableguardrail terminal and a mid-size vehicle thatleft the roadway during a snow storm in Iowa. Side impact crash tests should be performedon all narrow roadside objects like sign andluminare supports, guardrail terminals,narrow crash cushions and breakaway utilitypoles.

VehicleThe typical 820-kg small passenger vehicleused in other Report 350 crash tests was recommended for use in roadside hardware side impact crashtests. Unlike other types of accidents, there does not appear to be a relationship between vehicle mass andthe likelihood of severe occupant injury.(1) Only two-door models be used since the larger span betweenthe A and B pillars on two-door models creates a more demanding test. A small vehicle was chosen as thetest vehicle in order to minimize the amount of energy and momentum available to activate a breakaway,collapsing or yielding device. The roadside hardware side impact recommendations only specify a smallvehicle because side impact tests are supplementary to the more usual full-scale tests recommended inReport 350. If a guardrail terminal, for example, is soft enough to result in acceptable side impact

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StructuralAdequacy

NCHRP-B The test article shall readily activate in a predictable manner bycollapsing, breaking away, fracturing or yielding.

OccupantRisk

NCHRP-F The vehicle shall remain upright during and after the collisionalthough moderate rolling, pitching and yawing are acceptable.

SI-H The Head Injury Criteria (HIC) measured using a side impact dummy(Part 572 subpart F) shall be less than 1000.

SI-T The Thoracic Trauma Index (TTI) measured using a side impactdummy (part 572 subpart F) shall be less than 90.

SI-P The pelvic acceleration measured using a side impact dummy (part572 subpart F) shall be less than 130 g’s.

VehicleTrajectory

SI-V After the collision the vehicle trajectory shall not intrude into theadjacent traffic lanes.

Table 2. Roadside Hardware side impact crash test evaluation criteria.

performance with a small car and also has sufficient capacity to pass the end-on pickup truck terminaltests, there is probably no reason to test larger mass cars in a side impact crash test.

Impact ConditionsAs summarized in Table 1, the recommended impact conditions involve a full broadside impact (ö=90o

and Ùi=0o) at the center of the vehicle door at a basic impact velocity of 50 km/hr. A supplemental higherspeed 60 km/hr test is also recommended for situations where the performance of a device may bevelocity sensitive. A full broadside impact was selected for a variety of reasons. While the mean fixed-roadside object side impact angle is 56 degrees, full broadside impacts (those occurring between angles of45 and 105 degrees) represent over 60 percent of side impacts. Full-broadside impacts are lessdemanding experimentally and therefore result in a more repeatable test. Lastly, using full broadsideimpacts ensures that the SID is loaded in only the lateral direction early in the impact event. The centerof the door was selected because it is the practical worst case impact location on a two-door vehicle. Forthese reasons, the basic 50 km/hr full broadside test provides a field-relevant practical worst case testscenario.

Evaluation CriteriaThe usual Report 350 evaluation catagories are summarized in Table 2: structural adequacy, occupantrisk, and vehicle trajectory. Structural adequacy demands that response of the test device be consistentwith the intended performance of the device: breakaway device should breakaway and collapsing devicesshould collapse.

The most discerning response measures, however, usually involve the occupant risk criteria. There arethree occupant risk evaluation parameters shown in Table 2, all three are consistent with evaluationcriteria used in FMVSS 201 and 214 crash tests:

C The thoracic trauma index (TTI), C The head injury criteria (HIC) and C The pelvic acceleration.

The TTI and pelvic accelerations are identical to those used in FMVSS 214 side impact crash tests for two

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door passenger cars. The head is the most frequently injured part in side impacts with tall narrow objectslike luminares and utility poles so some measure of head trauma must be included in roadside safetyhardware side impact evaluation criteria.(1) The HIC is generally considered a frontal crash measure butit was included in these recommendations because NHTSA is also using the HIC to evaluate lateral headimpacts with the upper interior structure of the vehicle in FMVSS 201 tests.(10) The HIC is the bestavailable measure of the probability of serious head injury available from the biomechanics researchcommunity. A TTI of 90 represents a probability of severe occupant injury (e.g., AIS>3) of 0.16 and aHIC of 1000 represents a probability of severe occupant injury of 0.18 (e.g., AIS>3).(11)(12) The twoATD response measures, therefore, represent the same level of occupant risk of injury (there are no curvesfor relating pelvic accelerations to the probability of AIS>3 injuries).

Experience obtained during side impact crash tests of luminare supports showed that the ATD position atthe time of impact can have a dramatic affect on the HIC and TTI. This is generally not a problem inFMVSS 214 tests since the test device (e.g., the vehicle where the ATD is located) is not moving whereasin a roadside hardware crash test the ATD is accelerated with the impacting vehicle. Therecommendations shown in the FHWA report include normalizing equations to account for out-of-positionATDs. These normalizing equations have not been included in Table 2 because they were based on a verysmall sample of tests. Controlling ATD position and accurately accounting for an out-of-position ATD ina roadside hardware crash test is an area where additional research is required.

The vehicle trajectory criteria requires that the vehicle not intrude into adjacent traffic lanes after collisionand that it remains upright. Minimizing the chance of a second collision is the objective of the vehicletrajectory performance criteria.

Full-scale Crash TestsThe recommendations for roadside object side impact test and evaluation procedures summarized inTables 1 and 2 represent the best compromise between field relevance, harmony with other testingstandards and ease of testing. These procedures have been used to evaluate a slipbase and collapsingluminaire supports and four guardrail terminals as summarized in Table 3. All the tests summarized inTable 3 involve full-broadside nominal 50 km/hr impacts at approximately the center of the door on atwo-door 820-kg vehicles.

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Test Vehicle Device

Struct Occupant Risk Traj

Pass TTI HICPelvicAccel.

Pass Pass

1469-SI-6-85 88 Champ Slipbase Pole Yes 193 8026 198 No Yes

91S001 83 Colt Collapsing Pole No 145 398 — No Yes

91S003 83 Colt Collapsing Pole Yes 97 503 — Close Yes

91S036 85 Civic BCT No 117† — — No Yes

91S037 84 Civic ELT No 120† — — No Yes

91S038 84 Civic MELT No 103† — — No Yes

91S046 84 Civic MELT-SI Yes 37† — — Yes Yes

† TTI was estimated based on regression equations shown in (13).

Table 3. Summary of side impact roadside hardware crash tests using the recommended proceduresand evaluation criteria.(20)(13)

Slipbase Luminaire SupportTest 1669-SI-4-85 was a part of a test series of eight side impacts performed at a variety of velocities andimpact points.(20) The 1988 Plymouth Champ struck a slipbase luminaire support at 48 km/hr at a pointin line with the ATD head. The vehicle rolled into the pole at impact at an angle of 6.1o. The slipbase didnot activate resulting in 914 mm of vehicle crush and unacceptable ATD responses. None of the ATDresponses summarized in Table 3 for this test were acceptable. This test illustrates that high ATDresponses are common even when the amount of residual crush is relatively small.

Collapsing Luminaire SupportTwo tests of a collapsing luminaire support (tests 91S001 and 91S003) were performed as part of a seriesof side impact crash tests into a variety of luminaire and guardrail terminal systems (e.g., the 91Sxxx testseries).(13) In the first test a 1983 Dodge Colt struck the pole at 48 km/hr at a location midway betweenthe A and B pillars and centered on the occupant head. The pole activated and started collapsing asdesigned but the inertia of the pole caused a buckle to form about 4.5 m up the pole. The vehicle engagedthis “hook” causing large loads into the anchor bolts causing the welds between the anchor bolts and thereinforcing rods to failed. The weld failure separated the pole from the base. The vehicle sustained 406mm of crush on the side door and remained in contact with the pole. The ATD responses, given in Table3, show an unacceptably high TTI value and a low HIC value (the pelvis accelerations, unfortunately,were not measured). An investigation of the on-board film indicated that the ATD was 290 mm from theedge of the window, leaning in-board considerably farther than the usual 165 mm. This test exceeded theallowable TTI so the occupant risk criterion was considered not satisfied. Since the anchor bolt weldfailed, however, the test was considered to have not met the structural adequacy criteria.

Another test was run (test 91S002) in order to determine if the poor quality of the weld in the first testaffected the results. The second test involved a 1983 Dodge Colt striking the pole at 48 km/hr centeredont he occupant head as before. The response was similar to the first test with the pole initially activatingbut then buckling about 4 m above the ground. As in the previous test the vehicle engaged the buckle andpulled the pole failing at the base. The vehicle came to rest in contact with the pole and the impact caused

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229 mm of static crush, much less than the earlier test. The ATD responses in this test indicated anacceptable HIC and a TTI just over the acceptable limit of 90 g’s.

Breakaway Cable TerminalTest 91S026 was the first-ever side impact crash test of a guardrail terminal. A breakaway cable terminal(BCT) was struck by a 1985 Honda Civic Si at 59 km/hr at a point in the center of the driver-side door. The vehicle was perpendicular to the travelled way and the front of the vehicle was pointing toward thetravelled way. On impact the BCT nose collapsed against the first breakaway post of the BCT. The firstpost did not break causing 991 mm of static crush on the vehicle. An ATD was not included in thevehicle since it was expected to be a very severe impact with substantial deformations that would causeserious damage to the ATD. Since all components of the BCT are located below the ATD shoulder theHIC was considered to be nondiscerning. The TTI, based on regression equations based on pole tests, wasestimated to be 117 g’s. Since the estimated TTI was well above the n 90-g limit, the occupant riskcriteria was deemed unsatisfied. In addition, the structural adequacy criteria was deemed unsatisfied sincethe first post did not break and the system did not activate. The results of this test are shown in Figure4(a).

Eccentric Loader Breakaway Cable TerminalThe most notable difference between the eccentric loader BCT (ELT) and the BCT with respect to sideimpacts is the different shape of the nose. The ELT uses a corrogated steel culvert section and includes asteel loader arm inside the nose. It was hoped that the larger stiffer nose of the ELT would help distributethe load on the vehicle and result in better performance. The results shown in Figure 4(b), however, weremuch the same. The 51 km/hr impact did not fail the first post so the ELT did not activate as design. Thevehicle sustained 759 mm of crush and the TTI was estimated to be 120 g’s. The test failed both thestructural adequacy and the occupant risk criteria.

Modified Eccentric Loader Breakaway Cable TerminalThe modified eccentric loader BCT (MELT) uses a standard BCT nost with two horizontal plates inside.

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Figure 4. Results of 50 km/hr broadside side impacts with four guardrail terminals.

The results of this 48-km/hr side impact were much the same as those for the BCT and ELT as illustratedby Figure 4(c). The first post of the system, while seriously split, did not fail and the system did notactivate. The vehicle sustained 800 mm of static crush and the estimated TTI was 103 g’s so this test wasconsidered a failure as well based on both the structural adequacy and occupant risk criteria.

Modified Eccentric Loader Breakaway Cable Terminal further Modified for Side Impacts One additional test was performed using a MELT was a variety of modifications to improve the sideimpact performance. All the splice slots between the nose and rail were lengthened, the nose wasextended downward to contact the vehicle sill, and the first two posts were weakened with vertical slots. The results of test 47 km/hr test were considerably better resulting in the first and second posts breakingaway. The vehicle crush was 279 mm and the estimated TTI was a low 37 g’s. This test was consideredto have passed all the criteria listed in Table 2.

OTHER SIDE IMPACT TEST AND EVALUATION PROCEDURESSide impact test procedures and evaluation criteria from the National Highway Traffic and SafetyAdministration (NHTSA), the European Union (EU), and the International Standards Organization (ISO)are briefly reviewed and compared to the roadside safety side impact test and evaluation proceduressummarized in Tables 1 and 2.(14) (15) (16) While there are other standards (eg. Canadian, Australianand Japanese) the three discussed herein are considered the foundations for all other side impactstandards.

National Highway Traffic and Safety AdministrationThe automobile design and regulatory communities have been investigating side impacts for nearly 20years. Vehicle-to-vehicle side impacts account for approximately 60 percent of all side impact collisions

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TTI'GR%GLS

2

so NHTSA focused its research primarily on impacts between vehicles. NHTSA research in the 1970'sultimately lead to the adoption of FMVSS 214 in 1973. This first side impact standard involved aquasi-static door crush test on production vehicles. The door was crushed with a cylindrical impactor thatwas hydraulically pushed into the door until 305-mm of crush were obtained. The force-deflectioncharacteristics of the door were then used to assess the strength of the door.

Researchers and policy makers soon realized that the static crush test probably was not an effective meansof assessing side impact crashworthiness in actual collisions so NHTSA began research aimed at developing test and evaluation procedures for a full-scale side impact crash test. Sections S5 and S6 wereadded to FMVSS 214 in 1990. All passenger vehicles manufactured after September 1, 1993 are requiredto meet the requirements in subsections S5 and S6 of FMVSS 214 test and trucks, buses and multipurposevehicles with masses less than 2,725-kg will be required to meet the standard after September 1, 1998.Subsections S5 and S6 include test and evaluation criteria for a dynamic side impact crash test thatinclude a moving deformable barrier (MDB) striking the side of a production vehicle at a velocity of 54km/hr.(14) The impacting MDB and the struck vehicle are perpendicular at the time of impact (ö = 90E)but the four wheels of the MDB are “crabbed” at 27° such that the line of forward motion of the movingdeformable barrier forms an angle of 63° with the center line of the test vehicle (Ù i = 27E). The vehicle isimpacted such that a longitudinal plane tangent to the left forward edge of the moving barrier passesthrough the impact reference line within a tolerance of ± 50 mm. The ATD used must conform to therequirements of subpart F of part 572 of FMVSS 214, the so-called side impact dummy (SID).

There are performance requirements for both the ATD responses and the response of the vehicle. Vehicleresponses are described in section S5.3 and specify that the door must remained attached to the vehicleand latched during the test. Sections S5.1 through S5.2 describe the two ATD response requirements: theThoracic Trauma Index (TTI) and the maximum allowable pelvic acceleration. The TTI may not exceed85 g for passenger cars with four doors and 90 g for passenger cars with two door cars. The TTI iscalculated based on the accelerations recorded at the upper and lower ribs and the T12 spinal segmentaccording to the following equation:

where GR is the greater of the peak accelerations of either the upper or lower rib expressed in g's and GLS

is the lower spine (T12) peak acceleration expressed in g's. The second ATD response criteria requiresthat the peak lateral acceleration of the pelvis must not exceed 130 g's.

European Union DirectiveThe European side impact directive was adopted by the European Parliament and the Council of theEuropean Union (EU) on May 20, 1996. The EU side impact test involves a MDB striking a stationarytest vehicle at 50 km/hr. Unlike FMVSS 214 test, the forward motion of the MDB is perpendicular to thelongitudinal direction of the impacted vehicle (ö = 90E and Ù i = 0E).

The EU test specifies the use of a different ATD, the BioSID, with corresponding different evaluationparameters. The five BioSID performance criteria are:

C The head performance criteria (HPC) may not be greater than 1000 (HPC and HIC are identical), C The rib deflection criteria (RDC) may not be more than 42 mm, C The viscous criteria (VC) may not be more than 1.0 m/s, C The pubic symphysis peak force (PSPF) may not be more than 6 kN and C The abdomen performance criterion (APF) must be no more than 2.5 kN internal force (equivalent to

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external force of 4.5 kN).

In addition to the ATD evaluation criteria there are several other structural performance requirements forthe vehicle: C The doors of the car should not open during the test, C The ATD must be removed from the test vehicle without the use of tools,C No interior device or component can become detached or damaged in such a way as to increase the

risk of injury to a vehicle occupant.

International Standards OrganizationThe International Standards Organization (ISO), unlike the EU and NHTSA, has no regulatory authorityso the ISO is concerned primarily with developing standards that promote international exchange ofinformation and test results. As such, the ISO standards do not generally recommend any evaluationcriteria but are instead restricted to specifying test conditions. There are two ISO standards that involveside impact testing: ISO 10997 and the draft ISO pole-test standard. ISO 10997 specifies impactconditions and test methodologies that are essentially the same as those specified in the EU directiveexcept that no specific performance limits are given.(17) The ISO pole-test standard is being developed tofacilitate the development of side impact airbags in automobiles for impact with objects like poles andtrees.(16) Impacts with these types of objects are likely to involve contact with the head in addition to thethorax and pelvis.

A variety of ATDs are acceptable under this standard including the BioSID, the SID, the SIDIIs, theHybrid III and others. The impact should be aligned such that the 350-mm diameter rigid pole does notstrike the A or B pillar but strikes the door between them and the ATD head should be aligned with thecenter of the rigid pole. The vehicle is propelled sideways and should strike the pole at 30 km/hr. TheISO is still developing the pole-test standard so the specific details will probably continue to evolve in thecoming years and may vary from the values discussed in this paper. The most current draft of the ISOprocedures is contained in ISO Technical Report 14933.(18)

Comparison of Side Impact Test and Evaluation ProceduresAll the side impact test and evaluation criteria discussed above were developed to address specific aspectsof vehicle structural design, vehicle interior design or roadside hardware design. Though each standardhas unique features there are numerous areas where there is agreement across the standards. For example,the recommendations summarized in Tables 1 and 2 were developed specifically to harmonize with theNHTSA standards wherever possible such that there would be as much uniformity as possible between thetwo types of tests.

As shown in Table 4, there is already good agreement among the four principal side impact standardswith regard to impact conditions. Three of the standards use an impact velocity of approximately 50km/hr. With the notable exception of FMVSS 214, the other three recommendations use full-broadsidecollisions with no side-slip angle (ö = 90E and Ù i = 0E). In all cases the impact point is between thevehicle A and B pillars near the center of the vehicle door. The 50 km/hr full-broadside collisionrecommended in Table 1 is compatible with most the other side impact recommendations although thecrabbed impact orientation of FMVSS 214 is a noteable exception.

The evaluation criteria, shown in Table 5, used in both FMVSS 214 and in the recommendationssummarized in Table 2 are identical by design. The difference between the US and Europeanrecommendations is largely a function of the choice of an ATD. Developing more biofidelic ATDs is stillan active area of research. Harmonization by NHTSA, the EU and the worldwide biomechanics researchcommunity may develop better ATD evaluation criteria and the roadside safety community should be

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FMVSS 214 EU ISO Table 1Test Device Vehicle Vehicle Vehicle Roadside

Hardware - Velocity (km/hr) 0.0 0 30 0 - Orientation angle, ö 0N 0N 0N 0N

- Side-slip angle, Ùt 0 0N 0N 0N

- Impact point longitudinal cg center leading edge of device

Impactor MDB MDB Rigid Pole 820-kg vehicle - Velocity (km/hr) 54 50 0 50 - Orientation, ö 90N 90N 90N 90N

- Side-slip angle, Ùi 63N 0N 0N 90N

- Impact point Center center of doorcrushable face

Table 4. Comparison of impact conditions for side impact crash tests.

Evaluation Parameter Maximum ValuesFMVSS 214 EU Table 2

Anthropometric Test Device — ATD SID BioSID SIDHead Injury Criteria — HIC — 1000 1000Thoracic Trauma Index — TTI 90 (2 door) — 90

85 (4 door) — Pelvic g’s 130 — 130Rib Deflection Criteria — RDC — 42 — Viscous Criteria — VC — 1.0 — Pubic Symphsis Peak Force — PSPF — 6 — Abdomen Performance Criterion — APF — 2.5 —

Table 5. Comparisons of side impact crash test evaluation criteria.

willing to adopt the best available ATD measures in the future.

ISSUES AND DISCUSSIONThe roadside object side impact test and evaluation criteria summarized in Tables 1 and 2 represent thefirst step in developing side impact test and evaluation criteria for roadside hardware impacts. Therecommendations for roadside hardware side impact crash tests summarized in Tables 1 and 2 have beenbased on about 25 full-scale crash tests at the FHWA’s FOIL test facility over the past decade.(19) Withthe exception of four tests of guardrail terminals, these tests have been performed to explore the impactperformance in side impacts of a variety of luminaire supports. This body of test work and otherdevelopments in the broader automobile and highway safety communities have demonstrated severalissues that require additional research.

Anthropometric Test DevicesAs discussed earlier, one of the fundamental considerations in developing the side impact test andevaluation criteria summarized in Tables 1 and 2 was to take advantage of the extensive biomechanics

Ray et al 14

TTI HIC Pelvis AccelerationTest Device Value Time Value Time Value Time

(g’s) (msec) (g’s) (msec) (g’s) (msec)

1469-SI-#1 Rigid Pole 151 24 1593 27 71 231469-SI-#2 Rigid Pole 291 38 3385 26 199 211469-SI-#3 Rigid Pole 224 20 8684 19 157 231469-SI-#4 Slipbase Luminaire 193 25 8026 21 198 231469-SI-#5 Slipbase Luminaire 64 25 64 19 44 341469-SI-#6 Slipbase Luminaire 126 30 2191 45 158 261469-SI-#7 Slipbase Luminaire 14 48 150 43 43 181469-SI-#8 Rigid Pole 91 27 1996 26 25 2991S001 Collapsing ESV Pole 145 24 398 43 — — 91S003 Collapsing ESV Pole 97 18 503 23 — — 91S004 Slipbase Luminaire 82 13 2513 19 — — 91S005 Collapsing ESV Pole 84 18 139 29 — — 91S007 Slipbase Luminaire 413 11 17000 18 — —

Table 6. Time when the TTI and HIC occur in side impact crash tests with a variety of luminairesupports.

experience of the automobile design and regulatory community. The roadside safety research communitycan not match the resources of the vehicle design community in developing linkages between theprobability of occupant injury and crash test performance. It makes sense, therefore, to adopt theNHTSA’s FMVSS 214 ATD evaluation criteria and leave the issue of linking ATD performance to humanrisk to NHTSA, the automobile design community and the biomechanics research community. In short,all roadside safety hardware side impact evaluation criteria should be traceable to the ATD evaluationcriteria and human tolerance literature.

One objection to using instrumented ATD’s in roadside hardware crash tests is articulated in Report 350.

“There is no dummy capable of accurately simulating the kinetics and kinematics of an occupantfor oblique movements, that is, those in which occupant movement has both x and ycomponents.”(6)

This may well be true for redirectional impacts, but it is not a valid objection in side impact testing. First,the recommended impact orientation is a full broadside collision in part because this makes the earlyportions of the side impact a unidirectional event where the use of a SID is appropriate. Second, as isshown in Table 6, experience has shown that the TTI, HIC and pelvis acceleration nearly occur early inthe impact event when the vehicle motion is still primarily unidirectional (pelvis accelerations were notmeasured in the 91Sxxx test series so they are not reported). Table 6 shows the times when the TTI, HICand pelvis acceleration occurred in a variety of luminaire impacts. Some of these impacts involvecollapsing poles where the system “stroke” is very long, slipbase luminaires, and reigid poles where thedevice does not activate at all. In all cases, the HIC, TTI and pelvis acceleraiton recorded by the SIDoccurred in the first 50 msec of the impact. The complex yaw rotations typical of some side impacts withpoles occurs later in the event and long after the ATD has recorded the maximum accelerations that formthe basis of the HIC, TTI and pelvic acceleration. The SID is, therefore, an appropriate device to usesince the recommended impact conditions provide an essentially one-directional impact event when theSID is interacting with the vehicle interior

Accounting for ATD position is an important area of research since ATDs will always be prone to

Ray et al 15

1. Ray, M. H., L. A. Troxel and J. F. Carney III, “Characteristics of Side Impact AccidentsInvolving Fixed Roadside Objects,” In Journal of Transportation Engineering, Vol. 117,American Society of Civil Engineers, May-June 1991.

2. H. J. Hignett, "A Sideway Impact Test into a 12.2 m Lighting Column Fitted with a Breakaway Joint," Road Research Laboratory, Ministry of Transport, Report RRL LR241, 1969.

slipping out of position in roadside hardware side impacts. Ray and Carney developed normalizing curvesto adjust TTI and HIC values based on the observed position of the ATD at impact.(?) Unfortnuately,there was very little data to use in developing these curves so they are of questionable utility for generaluse. Additional research is needed to either validate these expressions or develop new methods foraccounting for an out-of-position ATD in side impact tests.(5)

Choosing the best available ATD is also a concern in developing side impact test and evaluatioprocedures. The biomechanics research community have been experimenting with a variety of deviceslike the Hybrid III, the bioSID, the EuroSID, the SIDIIs and combinations of features from each. Theroadside safety community should continue to maintain the same ATD performance measures used inFMVSS 201 and 214 tests and this may require switching to a different ATD in the future.

It is not wise to place an ATD in many roadside hardware crash tests since the chance of severelydamaging the ATD is very high. Since an ATD is a very expensive device to purchase, repair andcalibrate, there will be instances where it will not be cost effective to place the device in a hazardous testsituation where there will be large intrusions into the vehicle or a high probability of occupant ejection. Methods for estimating the ATD response based on the vehicle response and kinematics need to bedeveloped. These methods, however, must be traceable back to the ATD responses so that the risk ofhuman trauma may be estimated.

Vehicle Deformation Evaluation CriteriaOne of the Report 350 test evaluation criterion that is notably missing from the recommendations in Table2 are limits on the magnitude of passenger compartment intrusion. Since side impacts often result inlarge passenger compartment penetrations it might be expected that passenger compartment deformationwould play a major role in evaluating side impact collisions. As discussed above, the ATD responsesgenerally occur early in the impact event, often before there is significant passenger compartmentintrusion. Hinch, Hansen and Hargrave examined the relationship between HIC, TTI and vehicle crush ina series of eight side impact crash tests with luminaires. (20) They found that the correlation between HICand vehicle crush was both negative and very weak (R2 = 0.013) and the correlation between TTI andcrush was also very poor (R2 = 0.095). These results indicate that crush per se is a poor predictor of ATDresponse and therefore is also a poor predictor of occupant risk. The amount of vehicle crush is really justa measure of the amount of energy dissipated by the vehicle during the whole impact. Predicting thepotential for injury requires addressing not only the amount of energy dissipated but the rate at which it isdissipated. This is another area that requires a great deal more research to determine what therelationship between intrusion and intrusion rate and occupant injury is.

SUMMARYThe side impact test and evaluation criteria presented in Table 1 and 2 represent a good combination offield relevancy, harmonization with other agencies and experimental practicality. Side impact crashtesting is expected to become a more important part of the test and evaluation of roadside hardware in thefuture, especially guardrail terminals and luminaire supports. While there are important issues and areasfor further research as disccussed above, the recommendations described in this paper are a first steptoward developing better roadside hardware for side impact collisions.

REFERENCES

Ray et al 16

3. C. E. Buth, G. R. Samuelson, and R. M. Olson, "Crash Tests and Evaluation of HighwayAppurtenances," FHWA-RD-79-92, Federal Highway Administration, Washington, D.C.,September 1979.

4. J. Hinch, G. Manhard, D. Stout, R. Owings, "Laboratory Procedures to Determine the BreakawayBehavior of Luminaire Supports in Minisize Vehicle Collisions," FHWA-RD-86-106, Federal Highway Administration, Washington, D.C., February 1987.

5. Ray, M. H., and J. F. Carney III. Side Impact Test and Evaluation Procedures for RoadsideStructure Crash Tests. Report FHWA-RD-92-062. U.S. Department of Transportation, 1993.

6. Ross, H. E., D. L. Sicking, H. S. Perera, and J. D. Michie, “Recommended Procedures for theSafety Performance Evaluation of Highway Appurtenances,” National Cooperative HighwayResearch Program Report No. 350, National Academy of Sciences, Washington, D.C., 1993.

7. Ray, M. H., “Impact Conditions in Fixed Object Side Impact Accidents,” In Accident Analysisand Prevention, Pergamon Press, (in review), 1998.

8. L. A. Troxel, Ray, M. H. and J. F. Carney III, Accident Data Analysis of Side-Impact Fixed-Object Collisions,” FHWA Report FHWA-RD-91-122, Federal Highway Administration,Washington, D.C.,May 1994.

9. SAE J-211, Society of Automobile Engineers, Warrendale, PA, 1988.

10. NHTSA, “Federal Motor Vehicle Safety Standards: Occupant Protection in Interior Impacts,”Code of Federal Regulations, 49 CFR 571.201, Washington, D.C., current through October 14,1997.

11. R. M. Morgan, J. H. Marcus, and R. H. Eppinger, “Side Impact — The Biofidelity of NHTSA’sProposed ATD and Efficacy of TTI,” Report No. P-189, Society of Automobile Engineers,Warrendale, PA, October 1986.

12. P. Prasad and H. Mertz, “The Position of the United States Delegation to ISO Working Group 6on the Use of HIC in the Automotive Environment,” SAE Technical Paper, Society ofAutomotive Engineers, Warrendale, PA, 1985.

13. M. H. Ray and J. F. Carney III, “Side Impact Crash Testing of Roadside Structures,” ReportFHWA-RD-92-079, Federal Highway Administration, Washington, D.C., 1993.

14. NHTSA, “Federal Motor Vehicle Safety Standards: Side Impact Protection,” Code of FederalRegulations, 49 CFR 571.214, Washington, D.C., current through October 14, 1997.

15. “Directive 96/27/EC of the European Parliament and of the Council of 20 May 1996 on theprotection of occupants of motor vehicles in the event of a side impact and amending Directive70/156/EEC,” European Parliament, May 1996.

16. ISO, “Road Vehicles - Dynamic Crash Test Procedures for Evaluating Various Occupant-Interactions with Side Impact Airbags when the Impacting Object is a Pole, Moving DeformableBarrier, or High-Hooded Vehicle Simulation,” Report ISO/TC 22/SC 10/WG3 N 131. International Organization for Standardization, 1996.

Ray et al 17

17. “Passenger vehicles — Side impact with deformable moving barrier — Full scale test,” ISOTechnical Report 10997, International Standards Organization, 1996.

18. ISO WG3, “Road Vehicles — Test Procedures for Evaluating Various Occupant Interactionswith Deploying Side Impact Air Bags,” ISO Technical Report 14933, International StandardsOrganization, May 15, 1997.

19. Ray, M. H. and J. F. Carney III, “Side Impact Crash Testing of Roadside Structures,” FHWAReport FHWA-RD-92-079, Federal Highway Administration, Washington, D.C.,1993.

20. Hinch, J. A., A.G. Hansen, M. W. Hargrave, and D. R. Stout, “Full-Scale Side Impact Testing,”FHWA-RD-89-157, Federal Highway Administration, Washington, D.C., 1989.