News media have reported that the Tesla that drove into the back of a stopped fire truck in South Jordan (Salt Lake City) Utah on Friday May 11, 2018 had the semi-autonomous Autopilot engaged. In fact this conclusion is based on the driver’s own statement to police. While it may prove to be true there are many instances where drivers may say all kinds of things in order to protect themselves. The best source of such a conclusion would be the Tesla’s event data recorder and not what the driver may have stated.
South Jordan police have been quoted as stating that the Tesla was travelling at 97 km/h when it slammed into the back of the stopped fire truck and that that the female driver of the Tesla only sustained a broken ankle. It has been reported that a Twitter comment by Tesla’s co-founder, Elon Musk, indicated “What’s actually amazing about this accident is that a Model S hit a fire truck at 60 mph and the driver only broke an ankle…an impact of that speed usually results in severe injury or death”.
This is precisely the point that Gorski Consulting made in our news item of May 14th, 2018, only we questioned the police conclusions. The photograph of the damage to the front end of the Telsa did not match what the police have concluded. The police conclusions would suggest that the Telsa sustained a change-in-velocity (Delta-V) of close to 100 km/h because the fire truck would act as a moveable barrier that would result in limited post-impact motion. Such as massive change-in-velocity is not demonstrated in the relatively small amount of dissipated energy exhibited in the visible amount of crush shown in the photograph of the Tesla.
If the fire truck was stopped then the only chance of matching the police conclusions would be if that fire truck was not in gear and was pushed forward on rolling wheels thus contributing to some of the energy loss from the collision by allowing some additional post-impact motion of both vehicles. But even that possibility remains highly unlikely as severe crush should still exist on the Tesla. Obviously, the situation could be more plausible if the fire truck was actually travelling at a substantial forward velocity when the impact occurred such that the closing speed was much less than what has been assumed.