There has been a recent increase in the use of expert witness testimony relating to speeds of vehicles involved in collisions. This has resulted in a need for jurists and lawyers to become increasingly informed of the fundamental physical laws which form the basis of this testimony. The purpose in writing this paper is to discuss in a legal context the most commonly used physical laws in order to clarify an area which has become clouded by the use of incomplete data and erroneous hypotheses. After a consideration of the Nebraska position, the physical laws used in establishing speed on the basis of skid marks will be discussed with special emphasis on their application and limitations. The use of experiments by the expert witness, related physical laws, and a consideration of methods used by expert witnesses in Nebraska follow in that order.

I. Generally

II. The Nebraska Position

III. Extent of Testimony

IV. Physical Laws Relating to Skid Marks … A. Laws of Motion … B. Law of Conservation of Energy and Coulombs Law of Friction … C. Limitations of Calculations

V. Experimental Evidence

VI. Law of Conservation of Momentum and the Coefficient of Restitution … A. Speed Calculations Based on the Law of Conservation of Momentum … B. Newton’s Law of Recovery—Coefficient of Restitution

VII. Current Use of Expert Testimony

VIII. Conclusion

Appendix A: Possible Ranges of Pavement Drag Factors for Rubber Tires

Appendix B: Speed Estimates—Skidmark Speed Calculator