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This Case Study documents our company's efforts to demystify a baffling on-the-job fatality. A central part of the solution was Human Motion Capture. Our company was hired to find out what occurred when a railroad worker was fatally injured by a moving train while dismounting his own locomotive. Human Motion Capture was used in combination with aerial photography, nighttime videography, computer graphics, witness testimony and actual railroad equipment to produce a visualization video. The resulting visualization assisted all parties in understanding how this workplace fatality happened. This understanding led to an out-of-court settlement. Human Motion Capture enabled a scientifically accurate reenactment of the accident using actual equipment without producing a second fatality. This paper could aid anyone analyzing a serious workplace injury, either for reconstruction or worker safety training purposes.

This paper is the third part of a series of vehicle tests designed and conducted in order to further the understanding of vehicle handling and responses associated with a tire disablement event. The first two parts were published in SAE 970954 Drag and Steering Effects of Under Inflated and Deflated Tires [1], and SAE 1999-01-0447 Drag and Steering Effects from Tire Tread Belt Separation and Loss [2]. All of the test results included herein are presented in a manner to facilitate direct comparison to the previous test programs. Under inflated or deflated tires are known to cause increased forward drag and lateral steering effects on vehicles. These effects are commonly suggested to be the cause of driver loss of control and subsequent vehicular accidents. The increased drag and induced steering effects of under inflated and deflated tires are frequently an issue in an accident reconstruction.

Computer simulation and animation are used to build upon traditional methodologies for the evaluation of rollover accidents. The use of computer simulation allows for a more complete and detailed reconstruction than is possible with traditional methods. The use of computer animation allows a superior presentation of the reconstruction with detailed analytical results and real time visualization employing 3-D computer graphics. The accident scene and vehicle damage data are used together with results from rollover tests and computer simulation and computer graphics to reconstruct the vehicle path and vehicle dynamics in three dimensions. The significant previous papers, which provide the scientific basis for rollover accident reconstruction, are discussed with regard as to how this knowledge can be applied using HVE1 and 3-D Studio MAX2.

Tread belt separation and detachment is a common failure mode of radial tires. The accident reconstructionist is frequently asked to evaluate the effect of tread belt separation and detachment relative to the occurrence of an accident. Publications have previously been directed toward defining the effects of rapid tire deflation on vehicle drag and handling. However, little has been written about the singular effect of the loss of the tire tread belt relative to vehicle handling. The loss of a tread belt from a tire may be followed by rapid deflation. The combined separation and detachment event may have similar effects on vehicle handling as a rapid deflation event. To evaluate the effect of the loss of a tread belt without tire deflation, the authors tested tires prepared so that the tread belts could be intentionally separated while driving at speeds between 50 and 75 miles per hour.

HVE is a product of Engineering Dynamics Corp. designed to do scientific simulations and visualizations of vehicle accidents. It is a computer environment which combines a relational database and 3D graphics with physics programs. This paper is directed to readers who are users of HVE or are familiar with it and are considering becoming users. The purpose of this paper is to describe and discuss the types of available images and the methods for importing them into HVE. It will discuss the special considerations the authors have found necessary for the various types of images and for their incorporation into the HVE environment.

Computer imaging and animation can be extremely useful in analyzing vehicle accidents and illustrating the results. However the admissibility of computer images and animations in court is a concern. It is within the trial judge's discretion to decide whether a computer animation may be shown. Courts have accepted them in some cases and have rejected them in others. Aside from the legal issues, courts need to be sure that the images and motions are accurate and are based on recognized principles. Juries need to know these same things. This paper discusses the requirements which should be met to make computer images acceptable in a court of law and discusses methods for presenting an adequate foundation in court and the necessary explanations to a jury. The paper presents a systematic approach to laying the foundation for a court of law based on the author's own experience which employs the use of still images, photos, and diagrams. Case references are provided.

Under inflated or deflated tires are known to cause increased forward drag and lateral steering effects on vehicles. These effects are commonly suggested to be the cause of driver loss of control and subsequent vehicular accidents. The increased drag and steering effects of under inflated or deflated tires are frequently an issue in an accident reconstruction. This paper documents the results of a series of tests conducted to determine the magnitude and effects of under inflated or deflated tires on cars and light trucks. The test also establishes a method of testing that can be used to determine steering effects for other vehicles and speed conditions. Six vehicles ranging from a compact passenger car to a 3/4 ton pickup truck were tested. The test methodology was simple and produced repeatable test results up to the 45 mph speed defined as a limit for the tests.

Three dimensional computer imaging and animation have been widely used in industrial design. The use of computer imaging and animation for illustration in the court room has been widely recognized. Three dimensional computer animation also has analytical uses that apply to the accident reconstruction field. It can be used to evaluate visibility, timing of complex motions and is helpful in correlating vehicle damage to ground strikes. Used in concert with photogrammetry, 3D imaging can be very useful in determining the positions of objects pictured at the accident scene.

The speed change, Delta V, and the PDOF, principal direction of force, on a vehicle in an accident can be taken together to form a useful measure of accident severity. Many studies have correlated the combined effect of these with the statistical probability of an injury of a certain type and severity according to the AIS (abbreviated injury scale). The usefulness of this concept is enhanced by considering the effective Delta V and PDOF at occupant locations in a vehicle by taking into account the effect of the vehicle rotation. The method of calculating the Delta V at the occupant location is presented in this paper.

Vehicle crush deformation and energy equivalence relationships are widely accepted as technical accident reconstruction tools for estimating the change in velocity (Delta-V) during an impact. Delta-V has been accepted as a basis for evaluating damage severity and potential injury severity. Emori, Campbell and McHenry's work led to CRASH derivative type programs which are based upon a relationship between crush magnitude and Delta-V. SMAC derivative type programs utilize these principles while generating a time dependent analysis (simulation) by maintaining a continuous equalization of forces between the vehicles during the impact phase. This paper reviews basic principles and the relationships between Delta-V, kinetic energy, conservation of momentum, and barrier equivalent velocity which must be adhered to while performing this type of analysis. Several examples and frequently seen misunderstandings of these relationships are discussed.

When vehicles are launched (e.g. from a ramp) or drive off a cliff, large angular motions about several axes may ensue before the first impact. This paper presents a rational approach to solving for the large angular motions in terms of Euler angles, making use of Euler's equations for rotation of rigid bodies. Wheel forces are assumed to act vertically to the horizontal surface on which motion commences. The method is amenable to braking forces and side loads (not presented). The appendix provides a brief resume of the linearized equations of motion including braking.

The understanding of vehicle and occupant motions is at the heart of vehicle accident reconstruction. Testing is frequently done to understand, verify and demonstrate accident motions and dynamics. Tests conducted with scale models can give very useful results at a fraction of the cost of full-scale testing. The test results can be used to predict and understand the motions and dynamics of the full-scale vehicles and occupants. The proper design, construction and testing with scale models and the interpretation of the test results is governed by the principles of similitude. This paper presents an introduction to the principles of similitude. These principles have been the basis for scale model testing of structures and machines by engineers for many years. This paper presents the principles of similitude and shows how these can be applied to a vehicle which becomes airborne. The results of these tests are compared with mathematical predictions of vehicle motions.

A combination of metal roof passenger vehicles, an open top convertible passenger vehicle and enclosed multiple purpose utility vehicles were subjected to tip-over-the-front-end type pitch-over tests. The resulting roof crush and occupant compartment intrusion are presented in empirical and pictorial format. The tip-over roof crush performance is discussed relative to other recent side-over type rollover literature and to the FMVSS 216 on Roof Crush Resistance for Passenger Cars.

Vehicle accident analysis relies heavily on mathematics and the principles of conservation of energy and momentum and Newton's laws of motion. In order to apply these principles, it is first necessary to know the approximate vehicle motions. The analytical procedure is interactive using a combination of model analysis and computer-aided engineering analysis to determine linear and angular velocities and accelerations. Scale accident scene models combined with aerial photography to enhance realism has been extensively utilized in evaluation, analysis and presentation of vehicular accident reconstructions to non-technical audiences. Slide and video accident animations have been produced directly from aerial photograph enhanced models and have been used successfully in courtroom presentations since the 1970's.