Accident reconstruction methods

While reconstructing a car accident, there are several questions that must be answered, such as the movement of all the vehicles involved or of other people involved, or of objects from the point of first visual contact to their rest positions. Time history of velocities, positions as well as crash-related data such as velocity changes, deformation energies, or passenger loads must also be analysed. Methods to aid in accident reconstruction combine the simulation of pre-collision, collision, and post-collision dynamics for multiple vehicles. This paper presents trajectory and collision models used for accident reconstruction as well as useful optimisation strategies. The model for predicting the 3D kinematics of a vehicle's pre- and post-impact trajectory, which is based on a discrete kinetic time forward simulation of vehicle dynamics, has been described. The tyre model, steer angle, wheel braking, weight shift, and suspension effects have been introduced and a method of handling pre- impact yaw, braking, acceleration, and pre- impact steering have been outlined. The momentum-based collision model, which relies on restitution rather than vehicle crush or stiffness coefficients, has been defined and a method for dealing with secondary impacts, inter-vehicle friction, and impulse vectors with a vertical component have been explained. The second part of the paper deals with various collision models used to simulate the motion of the vehicles during the collision. Within the last part of the paper, various optimisation methods have been introduced which are used to generate the simulation results partially automated.