Here PQ...(always taking the long route...

)
I normally dislike Jalopnik....but this turned out to be handy!
It would seem that 29 of the 50 states have very clear 'must be passing' laws...and other others adhere to a "normal speed of traffic" law forcing slower-than-everyone-else cars to the right lane.
http://jalopnik.com/5501615/left+lan...e+by+state-map