The vast majority of traffic laws are state-by-state. The federal government can regulate only interstate (from one state to another). Anybody remember the "mandatory" 55 mph speed limit back in the '70s? Even that was set by each state; the federal government did some major arm twisting by withholding highway funds from states that didn't comply, but in reality each state was still free to set speed limits to whatever they chose.Like you guys are saying it could very well vary from State to State.
Read up on how this republic of ours works, it's really pretty interesting.