System-Based Energy and Momentum Analysis of Collisions

The persistent use of an absolute “impact speed” to characterize the “severity” of a collision rather than using the change in velocity (ΔV) or change of kinetic energy (ΔE) suggests persistent misconceptions among both technical and lay people regarding the relationship between those terms and other speed and energy measures in traffic collisions.

Through a review of first principles, supported by data from a set of crash tests designed to address the issues raised herein, this paper examines the relationship of the closing or relative velocity to “impact speed,” a speed (or velocity) across the ground (absolute speed) as the indicator of the extent of damage and the potential for injury in a given collision.