Some vehicles already log the speed -- it's routine in road traffic collisions to read it out of the vehicle computers. As I understand, it only covers the last

Some vehicles already log the speed -- it's routine in road traffic collisions to read it out of the vehicle computers. As I understand, it only covers the last few minutes prior to engine stop / loss of power. There's also the age-old method of looking at the speedometer: in a high-speed collision, the return spring tends to fail. Result is the needle gets stuck at the impact speed or close to it.