The effect of Mass properties on Road Accident Reconstruction

The paper investigates the influence of vehicle mass properties (mass, centre of gravity location, inertia tensor) on accident reconstruction. Considering the case of two colliding vehicles, the paper aims at defining which is the uncertainty of each mass property that should be prescribed to obtain an accurate accident reconstruction. The paper is divided into two parts. The first part presents a mathematical model, and its validation, able to perform a proper computation of the motion of vehicles before and after crash with the data that are usually collected by operators after the accident. In the second part, a theoretical analysis shows that an accurate accident reconstruction does need accurate measurements of both the centre of gravity location and the moment of inertia of crashed automobiles. Even a small error of 10% on the estimated value of the moment of inertia of one car or of an error of 100 mm in the location of its centre of gravity can lead to errors of close to 20% on the reconstructed velocities of the two cars before the accident. An existing test rig for measuring the c.g. location and the inertia tensor of crashed vehicles (pre- and post- impact), meeting the measurement accuracy determined on the basis of the sensitivity analysis, is presented.