On the Concept of Inter-Vehicle Friction and Its Application in Automobile Accident Reconstruction

Occasionally, an accident reconstruction analyst is confronted with the task of reconstructing an accident with configurations that do not lend themselves to straightforward analytical methods. The analyst may often turn to accident reconstruction software such as the various versions of SMAC and some impulse-momentum approaches like PC-Crash and VCRware. Within these programs there is a user-input variable often referred to as the inter-vehicle friction coefficient. Default values are typically provided with these software packages, so the user often doesn't have to do anything but leave the default value in place. However, in some collision configurations realistic solutions may not be arrived at when the default value is used. This can lead to the modification of the inter-vehicle friction value to tune the simulation result; typically in an effort to force the final rest positions of the collision partners to match documented accident scene evidence.

In this paper, the concept and application of the inter-vehicle friction coefficient is examined. Its usage in impulse-momentum methods and force-acceleration numerical integration methods (i.e. SMAC and its subsequent variants) is described and the relevant assumptions behind its use are discussed.