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VEHICLE LOCATION TECHNOLOGIES IN AUTOMATICVEHICLE MONITORING AND MANAGEMENT SYSTEMSJohn M. Watje a , Denis Symes b & Robert S. Ow ca Unisys, Incb U.S. Department of Transportation, Federal Transit Administrationc U.S. Department of Transportation, Research and Special Programs Administration, VolpeNational Transportation Systems CenterPublished online: 24 Oct 2007.

To cite this article: John M. Watje , Denis Symes & Robert S. Ow (1994): VEHICLE LOCATION TECHNOLOGIES IN AUTOMATICVEHICLE MONITORING AND MANAGEMENT SYSTEMS, I V H S Journal, 1:3, 295-303

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VEHICLE LOCATION TECHNOLOGIES IN AUTOMATIC VEHICLE MONITORING AND MANAGEMENT SYSTEMS

John M. Watje,' Denis Symes2 a n d Robert S. Ow3 I: Unisys, Inc. 2: U S . Department of Transportation, Federal Transit Administration 3: U S . Department of Transportation, Research and Special Programs

Adnlinistration, Volpe National Transportation Systems Cenrer

Automatic Vehicle Location (AVL) technologies are being used increasingly throughout fleet monitoring and management systems. AVL technologies have the potential for improv- ing fleet elliciency and providing better route planning and scheduling. However, bccause there are a number of possible AVL technologies from which to choose, transportation managers must analyze and evaluate their system needs and requirements before implement- ing any single or integrated approach to AVL. This paper is intended for a nontechnical audience and presents an overview of the AVL technologies available with some of their advantages and disadvantages.

Key ~wrds: Automatic Vehicle Location (AVL): Automatic Vehicle Monitoring (AVM); Advanced Public Transportation Systems (APTS); dead reckoning; proximity signposts; electromagnetic loop: ranging: trilateration: long range navigation (LORAN); Global Posi- tioning System (GPS).

I n Lewis Carroll's literary classic "Alice's Adventures in Wonderland," the Cheshire Cat is often remembered not just for his famous grin but also for his witty reply to

Alice's request for directions. When Alice is lost and wonders which way she ought to go, the cat tells Alice that it doesn't matter which direction she takes, since she doesn't know where she wants to get to anyway. In other words, since Alice doesn't know where she wants to go, any road will get her there.

Such is the dilemma faced by transportation managers when trying to improve the efficiency of their fleet operations. In demand response operations such as taxi fleets, package delivery, and para-transit, route planning and scheduling are often the keys to timely response and fleet efliciency. And today, with the current trend toward providing better customer service and information, even fixed route scheduling demands greater efficiency. Ridership, street traffic, weather, and road conditions all

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296 JOHN M. WATJE ef a/.

have an effect on such things as schedule adherence and customer satisfaction. But, without a way to effectively plan route scheduling, fleet operators may as well take the Cheshire Cat's advice and choose any method available. Fortunately, there are ways to improve fleet efficiency without facing Alice's dilemma of not knowing where to go. One way of improving fleet efficiency is through the use of vehicle location technologies in fleet monitoring and management systems.

VEHICLE LOCATION TECHNOLOGIES IN FLEET MONITORING AND MANAGEMENT SYSTEMS

Vehicle location technologies have been a part of large fleet monitoring and man- agement operations for many years. Early attempts at determining vehicle location were often simple and usually employed the use of a compass reading in conjunction with readily identifiable landmarks and street signs. A driver or vehicle operator merely reported the vehicle location by radio or telephone to a dispatcher who responded, as in the case of a taxi or delivery operation, by correlating the informa- tion with customer or delivery demands to provide the driver with a new customer destination or delivery route. Though minimal and seemingly primitive, this vehicle location method has nonetheless been both adequate and effective for many years, though useful mostly in small fleet operations. And herein lies its major deficiency, that is, it is a vehicle location method that is inadequate for larger fleets, the inefli- ciency compounding as the fleet grows larger and the operation more complex.

With the advent of larger and more complex fleet operations, the demand for more efficient ways of determining vehicle location also grew. Bus operations and police systems wanted to know exactly where a given vehicle was at any given time. The demand was met by the evolution of fleet monitoring and management systems in which Automatic Vehicle Location (AVL) technologies became an integral part. Dur- ing the 1960's, experiments with automatic vehicle location and monitoring began in Europe and the United States in the form of demonstrations and pilot projects to improve the efficiency of public transportation systems. In the United States, these experiments were conducted first at the Chicago Transit Authority by the Urban Mass Transportation Administration (UMTA), currently known as the Federal Tran- sit Administration (FTA), and later at other cities throughout the country. Police departments in metropolitan areas of Missouri, California, Massachusetts, and Texas soon followed with their own programs so that by 1980 most major cities and urban areas had either created fleet monitoring and management systems with some form of vehicle location method in place or were studying the feasibility of doing so.

Indeed, such was the demand for fleet monitoring and management systems that the Federal Transit Administration created a program aimed at evaluating the use of advanced technologies in public transportation systems. This program, the Advanced Public Transportation Systems (APTS) program, was set up as a part of the U.S. DOT initiative for Intelligent Vehicle Highway Systems (IVHS) and builds upon earlier evaluation work performed by UMTA. An example of this earlier work was a study known as the Advanced, Area-Coverage Automatic Vehicle Monitoring Pro- gram. In this study, UMTA evaluated the performance of four different location

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VEHICLE LOCATION TECHNOLOGIES 297

technologies to determine location accuracy, cost effectiveness, and feasibility of use. In fact, so encouraging were the early results of that study (See Table 1 for a summary) that UMTA continued to fund further studies throughout the 1980's.

However, because new technologies are continually evolving, becoming "smarter" as it were, one of the goals of the new APTS program was to research and evaluate "smart" technologies for use in transit systems, among which are AVL technologies. In fact, the APTS program is currently conducting AVL evaluations in various areas of the U.S. including Denver, Milwaukee, Dallas, and Baltimore.

AVL TECHNOLOGIES

Although, historically, these early AVL technologies were known as automatic vehicle monitoring or AVM systems, they are today most commonly referred to by fleet operators as automatic vehicle location or AVL. This change in terminology has come about in large part because the meaning of "vehicle monitoring" has also changed. While most of these early AVM systems were initially based on the idea of monitoring a vehicle's location automatically so that fleet efficiency could be im- proved by tracking schedule performance and adherence, the current use of "vehicle monitoring" has come to include such things as passenger counting, component failure (mechanical and electrical), and emergency response as well. Vehicle location, in other words, has simply become one component of vehicle monitoring which itself has now become but a part of an overall fleet monitoring and management system.

Early AVL technologies were based around the use of two methods of location: dead reckoning and proximity signposts. Neither of these location methods was inherently "automatic," however, and it was only with the use of another emerging technology that the term "automatic" could be used. That technology was the com- puter. It was with the incorporation of the computer into vehicle location systems that automatic vehicle location came into being, allowing fleet operators to monitor their vehicle operations continuously to determine where their vehicles were located at any given time. But with the introduction of computers into vehicle location systems came other means of determining vehicle location, some of which were adaptations of location technologies used by aviation and maritime systems. As a result, there are, in the 1990's, a number of vehicle location methods and technologies available to fleet and transit operators.

Currently, automatic vehicle location methods and technologies fall into three general categories: dead reckoning, proximity signpost, and ranging. Each of these categories consists of various technology sub-categories or methods by which the exact vehicle location is determined and each with its own advantages and limita- tions.

Dead Reckoning

In its simplest form, dead reckoning consists of compass and odometer readings used in conjunction with readily identifiable landmarks and street signs. The vehicle

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operator relays his vehicle position to a dispatcher who logs the time, location, and vehicle identification information. In its more complex form, however, dead reckon- ing consists of a variety of devices including a compass, gyroscope, odometer, clock, microprocessor, and radio. These devices measure and record such information as the vehicle heading, speed, and odometer reading which are then referenced to time, and in some cases, calculated position, by an onboard computer. The resulting infor- mation is relayed to the central computer dispatch station by radio, automatically and without the vehicle operator's assistance. The advantage to employing dead reckoning is that it is inexpensive to install and operate. The disadvantage to using dead reckoning is that it is prone to unpredictable and road dependent errors. For example, wheel slip, tire size due to tread wear and inflation pressures, road surface, and traffic conditions all affect the accuracy of the vehicle sensors used in dead reckoning. Moreover, these errors are accumulative in nature and result in having to employ some external means of referencing the AVL reported vehicle location to a known geographical location. The most common means of referencing a dead reck- oning system is to have the operator visually identify his position to a dispatcher periodically and compare that position to the current instrument reported position. Another means of referencing a dead reckoning system is to use proximity signposts.

Proximity Signposts

Proximity signposts, sometimes known as mileposts, are used to determine the proximity of a vehicle to a location device. There are two general categories of signposts, each of which may employ a number of electronic sensing devices for determining vehicle location. These two categories of proximity signposts are: sharp signpost and broad signpost. A sharp signpost is one that requires the vehicle to be in close proximity to the signpost sensing device whereas the broad signpost merely requires that the vehicle be within an approximate range of the sensing device. Sens- ing devices used for signpost technology are placed at predetermined locations such as street corners or intersections and consist of radio signal devices, optical scanners, or electromagnetic loops. Electromagnetic loops are usually buried under the road- way itself while radio signal devices and optical scanners are usually mounted on some overhead or curbside object along the roadway such as a signpost, street light, or utility pole. Each of these signpost devices typically uses a coded message for communicating the position of the vehicle to either the bus itself or directly to a central computer. The computer coordinates this coded location code with the vehi- cle identification number and determines the location of the vehicle which it then relays to a dispatch terminal.

Proximity sensors can be either active or passive devices, the nature of which can determine whether it is a sharp or broad signpost. For example, both optical scan- ners and buried electromagnetic loops have a narrow or limited transmit and receive range and thus are generally found in sharp signpost systems whereas microwave and radio frequency devices have a longer transmit and receive range and can be used effectively in broad signpost systems.

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Signpost systems consisting of microwave and radio devices operate by either broadcasting a coded radio beam from a transmitter mounted on a wayside "sign- post" to the vehicle o r by broadcasting from the vehicle to the signpost. When the vehicle reaches a point within the range or proximity of the radio beam, it interacts with the signpost device and locates or references the vehicle to the signpost. Each radio signpost device has a specified operating range or area in which the vehicle can be detected. For example, in a radio signpost design with a range of thirty meters, the vehicle must be within thirty meters of the signpost before the signpost device will trigger and begin the transfer of information between the signpost device and the vehicle. With some radio signpost devices the vehicle location information is pro- cessed and referenced at the vehicle and relayed from the vehicle to a dispatch sta- tion. With other radio signpost devices, the vehicle location information is relayed to a dispatch station from the signpost device itself. In either case, the location informa- tion can be relayed immediately o r stored for future access and use, depending on the signpost design and the level of information accuracy needed.

Electromagnetic loops, on the other hand, are often considered hybrid devices that operate in a manner similar to radio signpost devices in that they are dependent on a radio beam emitted from the vehicle only. The vehicle continually broadcasts a coded vehicle identification signal that is received by an electromagnetic loop buried beneath the pavement at a specified location or intersection. The electromagnetic loop acts as a radio antenna and relays the vehicle identification information to a central com- puter which matches the vehicle identification with the known location of the electro- magnetic loop. The electromagnetic loop is seldom used today as its reliability has been poor and its maintenance and operation costly.

Finally, while optical scanners were once thought to be a cost effective means of determining vehicle location and found their way into wide use with railway freight systems, their current use among transit and fleet operations is all but nonexistent. Optical scanners operate by emitting a laser or other optical beam to scan and read a bar code mounted on the side of a vehicle. The scanned vehicle information is then relayed to the central computer to locate the vehicle. Because the optical beam must be reflected back to the scanner to be read correctly, the technology is of limited use in transportation applications. Rain, fog, dirt, and reflected sunlight are sources of interference when using an optical scanner and thus present a number of technical problems that must be solved before optical scanners can be considered as reliable devices for vehicle location.

Some advantages to using a proximity signpost are that, when used in the broad signpost configuration, it is a relatively simple means of providing vehicle location, only moderately expensive, and adequate for most transit uses. Its disadvantages are that, to be used effectively. it requires a large number of devices and consider- able computer software overhead. When used in the sharp signpost configuration, accuracy requirements may dictate the use of additional devices, increasing the cost proportionately. Other disadvantages are that the actual vehicle location can be accurately determined only by referencing the signpost information to the vehi- cle odometer, thus requiring some onboard processing to be built into the vehicle itself.

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Ranging

Vehicle location by ranging is a method limited to the use of radio or microwave technologies. Ranging is simply a means of locating a vehicle through the use of radio navigation techniques. With ranging, a system of radio transmitters and receiv- ers, positioned at known locations and programmed to broadcast and receive at set times and frequencies, is used to measure the distance between the transmitter and the receiver. Although ranging systems may consist of either a single receiver with multiple transmitters or a single transmitter with multiple receivers, most ranging systems compute the location of a vehicle by measuring the time delay between the time of transmission and the time of reception. By using three or more time delay measurements, the vehicle location can be determined accurately. In transportation applications, the most common ranging methods used are trilateration, long range navigation (LORAN), and Global Positioning System (GPS).

Trilateration is a ranging method employing the use of multiple receivers to locate a single transmitter. A single radio transmitter is mounted on a vehicle and set to emit a time referenced radio signal. Remote receivers, placed at sufficient distance from each other and "tuned" to the vehicle transmitter's carrier frequency, receive and process the time referenced radio signal and determine the location of the vehi- cle. The vehicle location is determined by comparing the radio signal's time-of-arrival at the receiver with the time of transmission. By using three or more receivers posi- tioned at known locations, the time delays can yield direction, range, and location information. The time delay information is sent to a central computer which com- pares the delay information from the various receivers, computes the lines of posi- tion, and determines the point of intersect where the vehicle is located.

Long range navigation or LORAN uses a ranging method that is the reverse of trilateration. Rather than using multiple receivers to locate a single transmitter, LORAN uses a single receiver to locate multiple transmitters. With LORAN, a receiver is mounted in a vehicle and tuned to receive time referenced radio signals from multiple transmitters. Remote transmitters, placed at known locations and pro- grammed to broadcast at 100 KHz, are used by a receiver to determine the vehicle location. Since the LORAN transmitters, comprised of a system or "chains" of master to secondary transmitter stations, are time-slaved to each other, the vehicle receiver can determine its position by comparing the signal arrival times with the signal transmission times to measure the distance or range from the transmitters to the receiver. By measuring the ranges between the receiver and three or more LORAN transmitters, the LORAN receiver can determine the vehicle location by computing lines of position outward from itself to each of the transmitters.

Global Positioning System or GPS is similar to LORAN in concept but uses satellite based transmitters for its radio signal sources. Like LORAN, a GPS receiver is mounted in the vehicle and tuned to receive signals from multiple transmitters. With GPS, the transmitters are satellite based and are located at known points in earth orbit. A GPS transmitter emits a pulse modulated carrier referenced to a time source. Since all GPS transmitters are referenced to the same time source, the receiver locates its position relative to a GPS transmitter by comparing the time delay between the signal arrival time and the signal transmission time. The difference in time delay

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VEHICLE LOCATION TECHNOLOGIES 30 1

between the received signal and the transmitted signal determines the range of the GPS transmitter from the GPS receiver. By measuring the ranges of four or more GPS satellite transmitters, the GPS receiver can determine the vehicle location by computing lines of position outward from itself to the transmitters.

Although ranging methods are considered to be the most accurate and reliable of vehicle location technologies, they do have a number of inherent disadvantages that may inhibit their use in some transportation applications. Of these disadvantages, the most important is economic. Because most of the technology used in ranging was developed originally for defense specific applications, it was often highly sophisti- cated, and thus, expensive. Though commercialization has since reduced the cost of ranging technology, many large fleet operations still require considerable outlays for ranging technologies to be implemented fully. Moreover, since all ranging meth- ods use some form of radio beacon, they are susceptible to interference. This interfer- ence can be either mechanical or electromagnetic. Among the possible mechanical sources of interference are buildings, trees, foliage, and terrain. Electromagnetic interference can be caused by unshielded electrical sources, spurious radio transmis- sions, and industrial power stations. Since each source of interference can either reduce coverage area or introduce actual errors, ranging technologies must often be supplemented by other AVL technologies such as proximity signposts or dead reck- oning. For example, because GPS broadcasts on microwave frequencies, its reception is dependent on the receiver being in the "line-of-sight." Any interruption to the "line-of-sight" transmission from a GPS satellite transmitter will result in a blind spot or navigation outage. In other words, any tall building that stands between the receiver and the GPS satellite transmitter will interfere with the receiver's ability to lock onto the GPS transmission beam. Downtown areas of cities with row upon row of tall buildings will consequently present a "concrete" canyon effect on GPS vehicle location. The vehicle is blind to the GPS as long as it remains in the canyon. To compensate, the vehicle must use signpost or dead reckoning devices. Similar prob- lems exist for all ranging technologies and must be considered when designing a vehicle location system using these technologies.

TECHNOLOGY TRENDS AND FUTURE APPLICATIONS

Currently, the constraints imposed by budget cutting on local and federal levels is causing both transit agencies and manufacturers to look for even more cost effective ways of implementing AVL technologies. Fortunately, advances in manufacturing and technology are providing the means to do so. For example, signposts, once thought to be most effective in fixed route applications only, now show promise in random route applications as well. Because signpost devices are now being manufac- tured at much lower costs than previously, more devices can be placed throughout a transit system, thus enabling some transit agencies to expand their coverage area. In fact, several transit agencies are now experimenting with these newer, less expensive signpost devices to determine their overall cost and feasibility.

GPS devices are also realizing cost reductions and, in a number of transit agencies, are replacing Loran systems. Advances in receiver hardware and software design are

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Table I. Advanced, Area-Coverage Automatic Vehicle Monitoring ProgramPhase One Test Results

Time of PassageEdited Location Determination Accuracy

Location Test Results" for Fixed RouteSubsystem Manufacturer Fixed Route Random Route Operations

Proximity Signpost Fairchild 95% 81' 95% 220' 95% I sec.

(narrow beamwidth) 99.5% 125' 99.5% 430' 99.5% 2 sec.

Proximity Signpost Hoffman 95% 105'+ 95% 282'+ 95% 5 sec.

(broad beamwidth) 99.5% 188'+ 99.5% 367 99.5% 8 sec.

Radio Frequency Hazeltine 95% 191-325' 95% 270-460' 95% 15 sec.

(pulse trilateration) 99.5% 490-665' 99.5% 693-940' 99.5% 30 sec.

Radio Frequency Teledyne 95% 291' 95% 325-472' 95% 8 sec.

(LORAN-C) 99.5% 383' 99.5% 375·819' 99.5% 16 sec.

"Edited data results rnore nearly represent the performance levels that would have been achieved had the overall PhaseOne test system performed optimally or had the system deployment been optimal.

+Non-edited test result.

Source: Urban Mass Transportation Administration. Automatic Vehicle Monitoring Program Digest, U.S. DepartmentofTrnnsportation: Urban Mass Transportation Administration, Report N. DOT-TSC-UMTA-81-ll, Washington,D.C.: 19BI. p. 13.

not only improving the accuracy of GPS, but are reducing the observation andprocessing times so that the GPS system can become more efficient. When integratedwith geographical information systems, GPS devices, like other location technologies,are able to provide a spatial component as well. By incorporating digital mappingand display terminals, transit agencies can visually track a vehicle's location, thusimproving the overall system in cost effectiveness and usability.

CONCLUSIONS

Fleet operators who wander into this wonderland of AVL must often feel like Alicewhen she answers the Cheshire Cat and says that she doesn't care where she gets toso long as it is somewhere. With so many automatic vehicle location technologies tochoose from, fleet operators must sometimes feel as if it doesn't matter which tech­nology they choose so long as they choose one. But that approach would belie thepurpose of having AVL in the first place.

Although early attempts at employing AVL technologies in fleet operations wereaimed primarily at improving efficiency and providing increased safety and servicereliability, the uses for AVL have grown considerably. Perhaps the most important ofthese uses is in the data derived from each of the various AVL devices. Because AVLis not simply a technology for locating vehicles but a system of technologies, it mustbe seen in the context of the fleet operation itself Among the current uses of AVLdata in fleet operations are analysis and planning, customer services and travel infor-

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VEHICLE LOCATION TECHNOLOGIES 303

mation, safety and security, routing and scheduling, para-transit and handicap ser- vices, and transit and fleet management. Future uses of AVL data may include linking real-time vehicle location with geographical and spatial databases to provide timely and efficient transportation systems, especially demand response systems such as taxi, package delivery, para-transit and private transit systems, rental vehicles, travel information kiosks, and inter-modal travel systems.

As the uses for AVL data increase, so also do the demands on the location technol- ogies themselves. The decision factors surrounding the purchase and implementation of AVL technologies, therefore, become increasingly complicated. Moreover, since AVL is itself but an element in an overall fleet monitoring and management system, fleet operations managers must make decisions that account for their current system requirements as well as their future needs and are thus presented with a daunting array of choices. Because the fleet operation requirements determine the type of AVL technology used, fleet managers may have to integrate several different types of AVL technologies into a larger system. Decisions will have to be made that weigh the maximum location coverage possible with the most elTective means of doing so. In many cases, these decisions will result in compromise, with fleet managers deciding on a system of AVL technologies comprised of the best AVL methods available for the least cost.

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"Automatic Vehicle Location Makes Operations Run Smoothly." Metro Magazine, MarchIApril 1993: 41. Federal Aviation Administration. LORAN-C: An Introduction and User Guide. US. Department of

Transportation: Federal Aviation Administration. Navigation and Landing Directorate, Cambridge, MA: February. 1993.

Urban Mass Transportation Administration. Automatic Vehicle Monitoring Program Digest. US. Department of Transportation: Urban Mass Transportation Administration. Report N. DOT-TSC- UMTA-81-1 I . Washington. D.C.: 1981.

Carroll. Lewis. Alice's Adventures in Wonderland and Throueh The Lookine Glass New York. NY: - - Meridian. 1960.

Casey. Robert. Labell, Lawrence N.. and Schwenk, Judith C. Evaluation Plan for AVL implementations US. Department of Transportation. Research and Special Programs Administration, Volpe National Transportation Systems Center. Cambridge. MA: 1993.

Casey. Robert. Labell. Lawrence N.. and Schwenk. Judith C. Evaluation Plan for AVL Implementation in Four US. Cities. US. Department of Transportation. Research and Special Programs Administration. Volpe National Transportation Systems Center. Cambridge. MA: 1992.

Chin. Kam. and Phinney. David A. Navigation Technologies for Urban IVHS Applications lVHS Amer- ica 1993 Annual Meeting. Washington. D.C.: April 16. 1993.

Hurn. JeK GPS: A Guide to the Next Utility. Trimble Navigation. Sunnyvale, CA: 1989. Labell. Lawrence N.. Schweiger. Carol P.. and Kihl. Mary. Advanced Public Transportation Systems: The

State of the Art Update '92. US. Department of Transportation. Research and Special Programs Administration. Volpe National Transportation Systems Center. Cambridge, MA: 1992.

Reed, H. David. Roos. Mary. Wolfe. Michael, and DiGregorio. Ron. A Study of the Costs and Benelits Associated With AVM. US. Department of Transportation: Urban Mass Transportation Administra- tion. Oflice of Technology Development and Deployment. Washington. D.C.: 1977.

Schweiger. Carol L. Current Use of Geographic Information Systems in Transit Planning. US. Depart- ment of Transportation: Urban Mass Transportation Administration. Ofice of Grants Management. Washington. D.C.: August. 1991.

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