[SideburnsOfDoom]

> If both are moving in the same direction and one hits you in the back, you would not say they collided with each other

you are talking about a "Rear-end collision", correct? https://en.wikipedia.org/wiki/Rear-end_collision

[jncfhnb]

Yes. You would not say the lead car collided with the other in a rear end collision unless it was reversing.

> Typical scenarios for rear-ends are a sudden deceleration by the first car (for example, to avoid someone crossing the street) so that the driver behind it does not have time to brake and collides with it.