Comment by lukepothier

This isn't how driving works in practice. Suddenly stopping on a fast freeway isn't a reasonable thing to do unless it's absolutely necessary, and it's not reasonable to expect the following driver to constantly be considering the possibility that the driver in front will slam on the brakes for no reason. Insurance companies (at least in some parts of the world) have a standing agreement to just hold the following driver responsible when there's a collision like this, because in the majority of these collisions, the following driver is at fault. It's efficient for them to agree to this convention to avoid the cost of investigating each collision individually. This has led to the common misconception that the following car is necessarily responsible if there is a front-to-rear collision.