Who is at fault if Driver A was changing lanes and then Driver B rear ends Driver A and then Driver B leaves the scene of the accident?

Nobody is At Fault ... Driver B left the scene of an accident ... it was "B's" fault, but you do not know who Driver B is, so there is nobody to blame.

Probably better off anyway - chances are Driver B had no insurance, let alone a drivers license ... and even if they had stayed and were charged with being at fault, your own insurance would wind up repairing the damage you your vechicle.

AnswerDriver B- Sounds like he was an idiot! AnswerIf driver A was "cutting up" driver B while changing lanes (e.g. sees their exit and crosses two lanes full of traffic to get to it) then they may be at fault.

If driver B was frightened by this action they may leave the scene fearful that aggressive driver A is going to attack them. They may be making their way to a police station to report the incident.

AnswerFrom what I understand, driver B is by default the most likely to be at fault unless the facts are reviewed and point to another conclusion, ESPECIALLY if driver B is within X car lengths of driver A.

Lewis hamiltons