Who determines who is responsible for a traffic accident?

Figuring out who is at fault in an accident is a matter of deciding who was careless. For traffic accidents, State traffic laws provide guidelines by which liability may be measured. These rules apply not only to automobiles but also to motorcycles, bicycles and pedestrians. In some cases, a driver may be liable for an accident even if he/she was obeying, for example, the posted speed limit, if traveling at the posted speed was unreasonably careless given the weather or traffic conditions at the time.