Many investigators have used the equations of impulse, momentum and energy to analyze the changes in velocities when two vehicles collide. The equations generally include the classical coefficient of restitution which is used as a measure of energy loss. These equations and the coefficient are based upon large forces and short-duration contact between the two bodies. In all real collisions contact is over a surface, and in many vehicle collisions, momentary or permanent interlocking of deformed parts occurs over this surface. This causes a moment to develop whose impulse can significantly affect the dynamics; most authors neglect or ignore this moment (1, 2, 3, 4, 5)*. In this paper, the equations of impact of two vehicles are derived including the moment impulse. An impact moment coefficient is defined. The value of this coefficient determines the extent to which a moment is developed between the two vehicles during impact. Two examples are presented. The first is a simple classical problem of two rigid bodies impacting over a common surface and is presented to illustrate the concept of the impact moment coefficient. The second example uses data from an actual collision of two automobiles and shows that in accident reconstruction problems, an a priori value of the impact moment coefficient is often not needed.