Reconstruction methods typically are based upon impact velocity changes computed by one of two approaches. These are damage based or crush measurement techniques and impulse and momentum equation solutions. Crush measurement techniques have an analytical foundation based to a large extent on point mass collision theory, limited primarily to collisions of vehicles with a common final velocity at the contact surface. Impulse and momentum methods can treat a full, 2-dimensional collision with arbitrary restitution and friction coefficients. As such their analytical foundation is much broader than damage based or crush measurement methods. The energy loss relationship and the tangential correction factor form an important part of the crush measurement methods. These two relationships are derived in a more general fashion than has been available.
These two approaches are compared in this paper. The comparison focuses on the ability to accurately calculate energy loss. Data from some of the RICSAC experimental collisions is analyzed using the crush measurement model and the impulse and momentum model. The latter gives consistently low estimates of energy loss with accuracies ranging from −33% to 0%. The crush measurement model gives energy loss estimates which range from −55% to 109% of the experimental values. Though the crush measurement technique accuracy depends directly upon the ability to estimate of energy loss, the method appears to be less accurate in this respect than the impulse and momentum method.