IUse of a Microcomputer in

Transcription

1 IUse of a Microcomputer in Traffic Accident BYGEORGE T TAOK)+HAIM REIZES,AMIT REIZES,AND DAVID KOVEL T raffic accident reconstruction at- ~ tempts to explain exactly what happened in an accident before, during, and after impact occurred, and to determine precisely what factors contributed to accident causation. The investigator carefully examines all physical evidence available at the accident site, including: tire and gouge marks, debris, body parts and fluids, dimensions of vehicular damage, descriptions of injuries to passengers and pedestrians, and other facts that may be useful in analyzing and reconstructing the accident. The investigator then constructs a mathematical model of the traffic accident based on the principles of physics that apply to the type of accident being investigated. A set of pre-impact conditions that best fits the physical evidence found at the scene is calculated. Estimates of vehicular speeds; vehicular positions and orientations; time and distance studies; pedestrian trajectories; and the amount of yaw, roll, or vault experienced by any of the vehicles involved in the collision should be included in the parameters. This information is invaluable in revealing what factors contributed to accident causation and may be used to estimate the degree of liability incurred by those involved in the accident. Depending on the type or nature of a particular traffic accident, the solutions to the mathematical equations that simulate the accident may require extensive, time-consuming computations. Microcomputer software systems have been developed to perform these types of computations for different categories of traffic accidents. By using this type of system, an investigator may solve these equations quickly. Development of Computer Programs for Accident Twenty years ago, Cornell Aeronautical Laboratory, now called Calspan, developed the first comprehensive digital computer program for the purpose of traffic accident reconstruction in the United States. Three computer programs, HVOSM, SMAC, and CRASH, were developed by Calspan under contract to the U.S. Department of Transportation (U.S. DOT). The Highway Vehicle Object Simulation Model (HVOSM) program was the first program developed under Federal Highway Administration Contract CPR , between 1966 and The first version of HVOSM modeled the collisions of vehicles with fixed roadside objects. The force generated by the collision was assumed to be a linear function of the vehicular deformation. The program could also compute the trajectories of a vehicle under launch, vault, and other maneuvers, and has been used successfully to predict the trajectories of a vehicle subjected to unusual roadway geometries. The capabilities of this program are discussed in reports by Mc- Henry and DeLeys and Segal. The Simulation Model of Automobile Collision (SMAC) program was also developed under contract to the U.S. DOT by Calspan in the early 1970s. It modeled the collision between two vehicles in a two-dimensional, rectangular grid system. The impact force resulting from the collision is also modeled by a linear force-deflection function, similar to the impact force model of the HVOSM program. After initial conditions of velocity and position of the mass center in two rectangular and one yaw coordinate representing angular orientation are provided for each vehicle, the program uses numerical integration of the dynamical equations governing the impact of vehicles to tabulate the positions, velocities, and accelerations of both vehicles up to their final rest positions. The program is available from the National Center for Statistics and Analysis of the National Highway Transportation Safety Administration (NHTSA), U.S. DOT. Reports by McHenry3 and Solomon describe this program. Several microcomputer versions of traffic accident reconstruction programs are available. The third computer program developed by Calspan for the U.S. DOT in the 1970s, Calspan of Accident Speeds on the Highway (CRASH), is used more often than HVOSM and SMAC. An important fea- ITE JOURNAL onovember

2 ,,.,., ture of this program is a method developed by Campbells that computes the change in vehicular velocity due to impact, called delta V, from the crush depth deformation data of the vehicular collision. Combining the work-kinetic energy principle with the conservation of linear momentum principle, this program will compute pre-impact speeds and positions of vehicles, as well as other accident parameters desired by the investigator. An important parameter required as input for this program is the principal direction of force acting on each vehicle during the collision. The resulting accuracy of the computed variables is critically dependent on the accuracy with which this input parameter is estimated. The actual crush depth/ delta V relationships for the vehicles involved also affect the accuracy of the computed pre-collision variables desired. CRASH is also available from the National Center for Statistics and Analysis of NHTSA, U.S. DOT. Its capabilities are further described in McHenry and Lynch s CRASH 2 User s Manual. In Europe, the Equivalent Energy Speed-Accident (EES- ARM) program has been developed to model automotive collisions. It is similar to the CRASH program in that it requires an input parameter of an energy equivalent speed for each vehicle, which closely approximates the crush depth/ de1ta V relationship of CRASH. It combines the principles of conservation of momentum and the work-kinetic energy relationships to compute dynamic vehicular parameters. EES-ARM is described in detail by Zeidler. A useful overview of these programs is provided by Woolley, Warner and Pearl.8 Microcomputer Programs for Traffic Accident The digital computer programs described earlier were written for large, mainframe types of computers. Today, several microcomputer versions of traffic accident reconstruction programs are available. Although these microcomputer programs may lack some of the sophisticated capabilities of their mainframe counterparts, they are generally modeled after one or more of the programs described earlier. The CRASH %,...,....,. $ Figure 1. Angular intersection collision. program s use of the relationship between the change in speed and the resulting crush depth of each vehicle involved in the collision makes it a very popular program to follow. A similar relationship is included in many microcomputer programs. Although individual programs may vary in their input parameters and their output variables calculated, most have very similar requirements for proper use. Generally speaking, input parameters include vehicular weights and angular inertia properties, tire-road friction factors, length of skidmarks and gouge marks, vehicular crush depths and delta-v relationships, impact positions and post-impact trajectories to the final rest positions, and driver human factor information. Output variables usually computed by a program include pre-braking and pre-impact vehicular speeds, time and distance values before and after impact for each vehicle involved, post-impact trajectories of each vehicle to its final rest position, and postimpact angular spin velocities. Categories of types of accidents to be modeled include the single vehicle accident under braking, vaulting, flipping, overturning, and colliding with a fixed object. Two-vehicle collisions include head-on as well as offset head-on, rearend as well as offset rear-end, right angle, and oblique angle collisions. Some microcomputer programs can also model vehicle-pedestrian collisions. All of these microcomputer prqgrams utilize the dynamic principles of conservation of momentum and of work-kinetic energy along with vehicular crush depthl delta V energy relationships to mathematically model the mechanics of traffic accidents to compute the desired kinematic variables as they existed just before, during, and immediately after a traffic accident. Many of these programs are equipped with plotting subroutines capable of producing scaled diagrams of the pre-impact and post-impact trajectories of the vehicles involved in the traffic accident. These scaled diagrams can be extremely useful to a traffic investigator who must explain in a courtroom setting just how an accident occurred. A series of diagrams, sequencing the positions and velocities of vehicles before, during, and after impact, can be used very effectively to apportion fault or negligence in accident causation. There are many different microcomputer programs used in traffic accident reconstruction. The IMPAC program developed by Collision Safety Engineering is accessible by telephone or modem from a variety of personal computers. The program operates on an HP-9000 series under the UNIX operating system. The BLAQ BOX program, developed by Glennon, comes complete with a TI-74 computer (8-16K), a TI- PC324 printer, user s handbook, a small carrying case, and batteries. The ATAC I program is available on a disk for use with microcomputers and was developed by Advanced Traffic Accident Computer Systems. 1( It is also available as a pocketsize computer. The TAAR-2 program, developed by TAAR Safety 28. ITE JOURNAL. NOVEMBER 1989

3 Engineering, is available on a disk and can be run on IBM-PC compatible computers. This program models nine different categories of traffic accidents with special cases in each category. Application of TN-2 Software System The TAAR-2 Program will be used here to demonstrate the reconstruction of two actual traffic accidents. The Micro-CAD graphics package will also be used to illustrate the generation of scaled vehicular trajectory diagrams of the vehicles involved in each accident. Intersection Angular Collision of Two Vehicles The first accident occurred at the intersection of State Route 1 (SR 1) and Fernwood Pike in Potomac, Maryland, on a clear, but wet day. At this location, SR 1 is a four-lane, divided highway with a 49-foot wide depressed median. Each of the four lanes is 12 feet wide. The roadway has an asphaltic concrete surface with stabilized earth shoulders. The speed limit is 55 miles per hour. Fernwood Pike is an 18-foot wide, two-lane road with an asphaltic concrete surface. It intersects SR 1 at an angle. The speed limit on it is 35 miles per hour. A stop sign is located on Fernwood Pike for traffic approaching its intersection with SR 1. A 1982 Chevrolet Camaro traveling southbound in the left lane of SR 1 collided with a 1973 Buick Century crossing SR 1 from Fernwood Pike, heading eastbound. The Camaro weighed 3,000 pounds and had three passengers. It was deflected to its left after impact and rotated before coming to rest on the depressed median, about 80 feet from the impact point. It had extensive frontal damage with a maximum frontal crush depth of 18 inches. The Century weighed 3,922 pounds and had five passengers. It was deflected to its right, and rotated as it slid. It came to a rest about 166 feet from the point of impact. Its left side was extensively damaged, with a maximum side crush depth of 41 inches. The mathematical equations that model an angular collision of this type can be found in work by Reizes. 2 Using a coefficient of friction of 0.5 for the wet, asphaltic road surface, and a wet coefficient of friction for the median surface of 0.3, as well as the weights and vehicular damage measurements, a subprogram from TAAR-2 was used to reconstruct this accident. The subprogram calculated the speed of the Camaro to be 72 miles per hour, and the speed of the Century was calculated to be 15 miles per hour at impact. It was concluded that if the Camaro had been traveling at the legal speed limit of 55 miles per hour, there would have been sufficient sight distance for the driver of the Camaro to come to a complete stop before reaching the intersection. It was also concluded that there was sufficient sight distance for the driver of the Century to see the Camaro before entering the intersection from its position at the stop sign. Both drivers shared the responsibility for accident causation in this accident, although their relative proportions of responsibility were different. A computer-generated diagram of this accident is shown in Figure 1. Offset Fkontal Collision of Two Vehicles The second example reconstructed is an George T. Taoka is a professor of civil engineering at the University of Hawaii at Manoa. He teaches trafjic engineering and is a consultant in trafic accident reconstruction. He is an Associate Member of ITE. He has received a master s and a doctoral degree from the University of Illinois. accident that occurred on Barrington Highway on the island of Oahu in the State of Hawaii. In the vicinity of this accident, Barrington Highway is an undivided, four-lane highway, 44 feet wide. A double solid yellow line divides Honolulu-bound traffic from Kaena-bound traffic. The roadway surface is composed of asphaltic concrete, and there are dirt/ coral shoulders on both sides of the roadway. The speed limit is 35 miles per hour. The accident occurred on a clear, dry day. A 1966 Chevrolet Camaro, heading in the Kaena direction, in the left lane, crossed the centerline and collided with a 1977 Chevrolet pickup truck traveling in the left lane in the Honolulu-bound direction. The Camaro weighed 3,100 pounds and had an adult driver and a child passenger. The truck had an adult driver and no other passengers; it weighed 3,980 pounds. After crossing the centerline, the Camaro left 46 feet of skidmarks before impacting with the left front of the pickup truck, in an offset front collision. After collision, the Camaro was spun counter- Haim Reizes is a private consultant in trajjic accident P reconstruction, ~ and is the developer of the TAAR- 2- software system. He was formerly with the National Transportation Safety Board. He is a registered professional engineer and has lectured at universities in Europe and the United States. Amit Reizes is a David Kovel is a senior majoring in consultant to safety engineering TAAR Safety Engineering in devel- at the University of Maryland. He developed the Micro- mathematical modoping computer CAD plotting ca - els for solving accident reconstruction model cases. He is pability of the TAAR-2 software sy;tem. He is a consultant in computer applica- currently involved in developing techtions to trafic accident reconstruction. niques for coordinating electronic messages to serve on an electronic network for highway safety professionals. ITE JOURNAL onovember

4 clockwise. The pickup truck was deflected to its right and ended up in the right, Honolulu bound lane, rotated slightly in the clockwise direction. Although the driver of the Camaro was clearly at fault for crossing the centerline, an important question that arose was whether the driver of the truck had enough time to execute an evasive maneuver in order to avoid the accident, or to mitigate its severity. The equations that model a collision of this type can also be found in the work by Reizes. 12 Using a dry coefficient of friction of the roadway of 0.7, a subprogram was used to reconstruct this accident. This subprogram was used to calculate the time required for the Camaro to impact with the pickup truck, once it had crossed the centerline. This was calculated to be 1.23 seconds. Since it would take more than 1.23 seconds for an adult to perceive, react, and execute an evasive maneuver under surprise conditions, it was concluded that the driver of the pickup truck did not have sufficient time to try to avoid the collision, once the Camaro had crossed the centerline. A discussion of emergency maneuvers by drivers under surprise conditions can be found in work by Taoka.l The computer-generated diagram of this accident is shown in Figure 2. The relative positions and orientations of the vehicles involved both before and after collision are graphically illustrated in Figure 3. Conclusions The simultaneous solution of mathematical equations resulting from conservation of momentum and energy principles, coupled with force-deformation characteristics of vehicles, including human factors characteristics of drivers interacting with unusual roadway geometric design features, can be a truly formidable task for the accident reconstructionist. Using computer programs specifically designed to analyze and reconstruct traffic accidents saves the investigator time and effort. There are many different programs available that offer versatility and easy manipulation. There are some disadvantages in the use of microcomputers in reconstructing traffic accidents. Although most existing programs have been modeled after successful mainframe programs such as the CRASH program, not all features of existing programs have been verified by II I I Ill F TAAR -CFISENO. ) farringtonhighvay - 35 KP,H, Km(------)I022,UU 1 I L ,,. :61n: la SfCm2Um v-1 tff +~~] t i,/%. t m w 222sum 12nR2 IIPm % V-2 aulilmu $122LEu XEiE!_l SCENEDIAGRAM Figure 2. Offset frontal collision. MAf9Mfow Iwws ml ff e mllm Ma t-w $ e~ Qz? v-2 Figure 3. Accident dynamics of offset frontal collision. Esl 2W1 ACCIDENT DYNAMICS field crash testing of vehicles. The use of particular automobiles involved in a spea relationship between vehicle crush cific traffic accident. depth and the delta-v change in ve- The angular spin of the post-impact locity of a vehicle requires extensive trajectories of vehicles also has been force-deformation characteristics of dif- shown to differ with the angular yaw ferent models of automobiles. Such in- characteristics measured in crash tests of formation is not always available for the vehicles. The properties that predict ve- J 30. ITE JOURNAL onovember 1989

5 hicular angle changes may be difficult to estimate accurately for the conditions of a particular accident. When these parameters cannot be accurately measured, the best a microcomputer program can do is to give estimates of upper and lower bounds of vehicular speeds and positions before, during, and after collision. The accuracy of these upper and lower bounds depends on the accuracy of the input parameter estimates. As long as the accident investigator is aware of the limitations of these programs, he or she will find them a useful tool in the reconstruction of traffic accidents. The cost of most programs is reasonable, and the accident investigator has a wide selection to choose from. References 1. McHenry, R. R., and DeLeys. Vehicle Dynamics in Single Vehicle Accidents Validation and Extensions of a Computer Simulation. Report CAL VJ-2251-V-3. Buffalo, N. Y.: Calspan Corp., December Segal, D.J. Highway-Vehicle Object Simulation Model; Report FHWA-RD- 162, Vols, 1, 2, 3, and 4. Washington, D. C.: FHWA, U.S. DOT, February McHenry, R, R. Development of a Computer Program to Aid in the Investigation of Highway Accidents; Report CAL VJ V-1. Buffalo, N. Y.: Calspan Corp., December Solomon, F?L. The Simulation Model of Automobile Collisions (SMAC) Operator s Manual, Accident Investigation Division, NHTSA. Washington, D. C.: U.S. DOT, October Campbell, K. Energy Basis for Collision Severity; Paper No Warrendale, Penn.: SAE, McHenry, R. R., and J.P. Lynch. CRASH2 User s Manualj PB Springfield, Va.: National Technical Information Service, September Zeidler, F. Accident Research and Accident by EES-ARM, Paper No , Publication P-159, Field Accidents, Data Collection, Analysis, and Methodologies, and Crash Injury s. Warrendale, Penn.: SAE, Woolley, R. L., C.Y. Warner, and T.R. Pearl. An Overview of Selected Computer Programs for Automotive Accident ; Transportation Research Record Washington, D. C.: Transportation Research Board, Glennon, J.C. BLAQ BOX; ITE.lournaf 58 (February 1988): Advanced Traffic Accident Computer Systems, Inc. ATAC I, Accident Reconsfrucfion Journal 1, No. 3 (June, 1989). Reizes, H. Microcomputers Aid Traffic Accident Analysis and, The Police Chief (July 1986): 63. Reizes, H. The Mechanics of Vehicle Collisions. Springfield, 111.:Charles C. Thomas, Taoka, G.T. System Identification of Safe Stopping Distance Parameters. Honolulu, Hawaii: University of Hawaii, ~ Keen UD with the State of the Art You ll ~ain a-better understanding of technological and research advances throughout the world with these four reports from the Organization for Economic Co-Operation and Development. Dynamic Traffic Management in Urban and Suburban Road Systems This report provides an assessment of dynamic trafllc management stratq$es and systims with special emphasis on applications of advanced technologies. OECD, 1987,100 pp. Publ. No. LP-12~ $16. Toll Financing and Private Sectir Involvement in Road Infrastructure Development This report examines the current use of toll financing in OECD nations and other nations and summarizes the conditions under which toll financing is likely to be successful baaed on actual experiences. Included are discussions of major road financing options, economic theory on toll roads, additional costs due to tolls, and review of current practice. OECD, 1987,150 pp. Publ. No. LP-13@ $18. Road Accidents: On-Site Investigations Detailed accident surveys are a valuable tool for assessing and helping to improve policies to prevent road accidents and reduce their severity. This review of the latest knowledge and research focuses on the contribution that multidisciplinary on-site investigations can make to traffic safety. OECD, 1988,104 pp. Publ. No. LP-137; $ Route Guidance and In-Car Communication Systems Car manufacturers and traf tlc managers are making more and more use of advanced information and communication technologies. This report reviews systems and developments in OECD countries and emphasizes the growing importance of developing international standards and joint research. OECD, 1988,104 pp. Publ. No. LP-13($ $ To order, send payment tn Institute of Transportation Engineers, 526 School St., S.W., Suite 410, Washington, DC USA. FAX 202/ Add 10% for shipping and handling (15%outeide U.S. and Canada); minimum chipping and handling charge is $5. Please include publication number and your daytime telephone number on order. To order by phone, cell the ITE Bookstore at 20!M ITE JOURNAL. NOVEMBER