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A personal computer program for drawing accident sites is described. The program design is reviewed and hardware requirements are defined. Standard features are explained and features unique to the needs of the accident reconstructionist, such as photogrammetry and a built-in accident site template, are presented. Its use with other computer accident reconstruction programs is illustrated. It is seen that the scaled accident site diagram provides an important element to the reconstruction, both as an analytical tool as well as a presentation tool.

The two procedures, DAMAGE and OBLIQUE IMPACT, which are used by EDCRASH for computing delta-V, are described in detail. Enhancements in EDCRASH Version 4 which improve the DAMAGE method of computing delta-V are also described. The advantages and disadvantages of each method are explored, and the numerical and graphical output and use of warning messages are reviewed. In general, it was found the two methods are complimentary: The DAMAGE procedure is best-suited for the conditions in which the OBLIQUE IMPACT procedure is least-suited, and vice-versa.

The EDSMAC personal computer program for use by accident investigators is described. The input data requirements are reviewed. The general calculation procedures are discussed and the specific procedures for computing delta-V are explained in detail. The method, based on equalizing the force between the vehicles at all times during the impact phase, is seen to be simple in concept but extremely complex in practice. The numerical and graphical output and warning messages are reviewed. Applications of the program are illustrated. The major benefit of EDSMAC is the ability, using graphics, to provide an analytical method illustrating how an accident may, or may not, have occurred.

Several computer programs are used by accident investigators to reconstruct motor vehicle accidents. These programs are seen as valuable tools by most investigators. However, it is also clear the programs are sometimes misused. This paper addresses five different types of computer programs used by accident investigators and discusses their proper and improper use. Most frequently, misuse is due to the lack of a thorough understanding of how the programs work. A series of recommendations is presented to help investigators properly use the programs.

Motor vehicle accident researchers have used the CRASH computer program for some time. Over the years, the code was upgraded until it reached its present and popular form, CRASH3, which runs on a mainframe computer or minicomputer with a sizeable memory capacity. A new version of the program, EDCRASH, has been developed which runs on personal computers using 128K of memory. This paper describes and compares this program with its mainframe counterpart. The program performed the same function as CRASH3, but was designed as a screen-oriented program utilizing the environment of the personal computer. Its design also allowed for file saving, graphics, routing of output, and interfacing with other accident reconstruction programs. For most accident types, the results for both programs were identical. However, for some types the results were different.

The accuracy of the CRASH computer program was evaluated in terms of its ability to estimate impact speed. A comparison of the results from CRASH2, CRASH3 and EDCRASH were presented along with measured results from twelve staged collisions. Statistical analysis of these results revealed the impact speeds estimated by these CRASH programs were within −6 to +7 percent of the combined impact speeds at a 95 percent level of confidence. Using EDCRASH's extended features to optimize the input data improved the range to within −3 to +3 percent of combined impact speeds. An example was used to illustrate the use of the confidence intervals to estimate the expected range of impact speed for a given reconstruction. The results for oblique collisions were found to be significantly more accurate than the results for collinear collisions.

The accuracy of the SMAC computer program was evaluated in terms of its ability to predict the correct paths and damage profiles for vehicles involved in a crash. A comparison of the results from SMAC and EDSMAC were presented along with measured results from twelve staged collisions. Statistical analysis of those results revealed the average path error was 25 to 29 percent and the average damage profile error was 109 to 287 percent. A procedure was presented for improving the match between simulated and measured paths. After using this procedure, the average path error was reduced to -2 to 7 percent and the average damage profile error was 54 to 186 percent. CDC predictions were very good. Damage profile errors, which did not reduce the program's overall effectiveness, were the result of the way the program computes inter-vehicle forces, leading to a recommendation that the algorithm be reformulated to include an initial force coefficient.

When an automobile is driven on wet roads, its tires must remove water from between the tread and road surfaces. It is well known that the ability of a tire to remove water depends heavily on tread depth, water depth and speed, as well as other factors, such as tire load, air pressure and tread design. It is less well known that tire tread depth combined with placement can have an adverse effect on vehicle handling on wet roads. This paper investigates passenger car handling on wet roads. Flat bed tire testing, three-dimensional computer simulation and skid pad experimental testing are used to determine how handling is affected by tire tread depth and front/rear position of low-tread-depth tires on the vehicle. Some skid pad test results are given, along with corresponding simulations. A literature review also is presented. Significant changes in tire-road longitudinal and lateral friction are shown to occur as speed, tread depth and water depth vary, even before hydroplaning occurs.

A major component in reconstructing motor vehicle accidents is the use of accurate data about the vehicles involved in the accident. Whether the reconstruction is done manually or with the aid of computers, the accuracy of the reconstruction is directly proportional to the accuracy of the vehicle data. Unfortunately, the vehicle data is not always available from the actual vehicles involved in the accident. In these instances, the reconstructionist must obtain data that best approximates the original vehicles. In lieu of finding, measuring, and weighing identical vehicles, the data is available through publications, trade associations, and other common sources. This paper describes these sources and how the information can be obtained.