The first part of this animation demonstrates how a particular guard rail end treatment design is intended to dissipate impact energy. The guard rail is designed to telescope and absorb the speed of a vehicle impacting it, bringing the vehicle to a safe stop. The second part of the animation progresses into the sequence of events related to an actual accident in which a large SUV impacts this type of guard rail. The system fails to collapse correctly, the w-sections of the rail bind, causing the rails to buckle and separate. The rails penetrate the occupant compartment, fatally injuring the right front passenger. Our engineers were engaged to complete an accident reconstruction of the event and to explain how the system failed. The accident reconstruction was based on our scene, vehicle, and guard rail inspections