Interestingly, while road traffic in the U.S. keeps to the right, railroads in the U.S. keep to the left as they do also in the U.K. The Engineer (Engine Driver in the U.K.) sits on the right side of the locomotive and the trains pass right side to right side.
I remember reading that the the reason that British drivers and others keep left derives from the railroad tradition, and American drivers keep right because the board upon which the wagon driver sat pulled out of the left side of a Conestoga wagon.
A not really related bit of trivia is that, while the command pilot of an airplane universally sits in the left seat, the command seat of a helicopter is the right seat (for a completely different reason that the ones mentioned above).