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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.

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.

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.