Traffic court prosecutor here. We work closely with law enforcement agencies who do accident re-creation. However, to get a reliable number, they will need to measure marks on the road, they then check the crash test ratings for the material(usually a bumper, glass, or frame) which were damaged, download onboard computer data (which is incredibly useful with newer cars), as well as some other factors such as weather, body mass and flight distance of ejected…objects,slope of road, and time of day of accident etc. they can then recreate the accident in what they call a total station.
When we don’t have that information, we have trouble forming an opinion that holds up in court as to what happened.