The application of a USDOT Crash-Like Computer Program Crash/Trajectory in Forensic Engineering by Robert L. Hess, Ph.D. and Joel T. Hicks, P.E.

In 1987, my young daughter was painting on office paper in her grandparent’s home. Her grandmother gave her the paper to use for this purpose. Together my daughter and her grandmother used the unprinted side of that paper to create water color pictures.

Imagine how delighted I was to find that the back side of the paper they had used contained part of a paper co-authored by my father. I have retyped what I found so that is legible for the reader of this blog. Sadly, not all of the pages are here . I found that you can download this full paper on-line at a cost of $25.00. I did not pay the fee, so this is only a sampling of the full document. Here is the link for the retrieval of the full document…

The Application of a USDOT CRASH-LIKE Computer Program CRASH / TRAJECTORY in Forensic Engineering

Part A: Mathematical Basis and General Capabilities by

Robert L. Hess, PhD

Joel T. Hicks,P.E.

(N.A.F.E. #049 Member)

Automotive accident reconstruction can be dramatically assisted and improved by the use of microcomputers which are programmed to utilize the vehicle damage and accident scene data. CRASH /TRAJECTORY is such a program and is based upon a main-frame computer program developed by the U. S. Department of Transportation. The federal program has been personalized and improved for use by legal and engineering offices faced with the task of interpreting actual accident cases. Where the federal program did not allow the user full access to the internal data tables and the output of the program’ s equations, these new programs do, through the use of user friendly menus and tables.

Introduction to the Underlying Mathematical Principles.

The laws of physics which underlie CRASH/TRAJECTORY are those which relate FORCE to changes in MOMENTUM and to changes in KINETIC and POTENTIAL ENERGY. These are based upon Newton’ s Laws, universally accepted as governing mechanical phenomena involving forces, mass and motion. To use these laws knowingly it would be good to review a few definitions and ideas of the physics of motion. This will be done in the next few paragraphs after which we shall turn to discussion of the program.

A body of mass (mass is the expression of the weight of a body in the gravitational unit named ‘slugs’) which is moving is said to have a VELOCITY and a LINEAR MOMENTUM. First note that there is a subtle difference between the two words SPEED and VELOCITY. Speed i s a measure of the magnitude of the rate of change of position of a body with time. Speed is measured in miles per hour or feet per second (MPH or ft./sec.).Speed does not in itself provide any information as to the direction of motion of a body, the word ‘velocity’ does. Combining the ideas of a body’s speed and direction of motion creates a VECTOR quantity, the VELOCITY VECTOR, or for shortness, the ‘velocity’. Velocity is a vector, i.e., an arrow-like quantity, with both magnitude and direction properties and would be described in writing as say, 45 MPH southward. A vehicle weighing 3220 pounds has



(“Blueberry” was a favorite stuffed animal)

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