A two-dimensional impact model with a capability of reverse calculation has been developed to reconstruct various types of automobile collisions. The model consists of a law of conservation of momentum and introduces a normal restitution coefficient and a tangential restitution coefficient at the impact center. Sixteen car-to-car impact tests, including side swipe type collisions, were conducted to obtain primary data for validating the model and improving its reliability in accident analysis. The relationship of the normal and tangential restitution coefficients to the collision type was obtained with a generalized impulse ratio from the analysis of test data by using the impact model.This paper presents the formulas used in the model and demonstrates their applications to accident analysis. The following analytical formulas are introduced: The relationship between energy loss and delta-V. The relationship between restitution coefficients and energy loss. The relationship between equivalent friction coefficient and tangential restitution coefficient.