Modern vehicles are designed to deform in a controlled way, so that the structure absorbs the energy of an impact rather than the people inside. Because that deformation is engineered and tested, it is also readable. The depth, profile and location of crush, and the stiffness of the structure that crushed, together tell an engineer how much energy was absorbed, and from that the change in velocity each vehicle underwent.
Delta-V, not speed
Most arguments are about speed. The quantity that governs what the occupants felt is delta-V, the change in a vehicle’s velocity during the impact itself. A fast car in a glancing contact can experience a small delta-V; a stationary car struck from behind can experience a large one. Delta-V, with the direction of the force and the duration of the impact, is the quantity a medical expert needs from the engineer, and it is where the engineering evidence in a low-velocity impact claim actually sits.
What the work involves
- Damage assessment from the record. Repair estimates, photographs, engineers’ reports and any recorded data. Photographs are evidence of what a camera saw; they are not measurements, and the report says what they can and cannot support.
- Crush and energy analysis. Stiffness data derived from published crash tests, applied to the crush profile measured by others or estimated from the photographs, with the uncertainty in each input carried through to the result.
- Consistency. Whether the damage to each vehicle matches the other in height, overlap, direction and severity, and whether it matches the accounts given.
The limits, stated
Crush analysis is powerful and bounded. Hidden structural damage, repairs carried out before the vehicle was photographed, missing photographs and unknown stiffness values all widen the range. An honest report gives the range, explains what drives it, and says plainly when the evidence does not allow a conclusion. That is more useful to a court, and more robust under cross-examination, than a precise figure the evidence cannot bear.
