RDoc
2021 Prerefresh Model S
I stand corrected. Two cars hitting each at 40 mph is not the same as hitting a wall at 80 for the reasons stated, there's half the energy compared to hitting the wall. Hitting a parked car at 80 is a bit more ambiguous since it depends on what happens after the collision. If the parked car is free to move it will carry away some of the energy in it's velocity, if it is prevented from moving the energy is all absorbed between the two cars.