Crandall v. Nevada

73 U.S. (6 Wall.) 35, 18 L.Ed. 744 (1868). States cannot tax the RIGHT to travel, into, from or across a State. Crandall was traveling by train to another State but was thrown off for refusing to pay a $1 tax when it stopped at the border. This does not address the 'privilege to drive', which is the use of a 'vehicle' in commerce (hauling goods or passengers for hire). Be aware of the difference when arguing whether you're 'driving' a 'vehicle' or merely exercising the right to travel in your car (it's not really yours if the State has the manufacturer's Certificate of Origin in THEIR possession, but that's another issue).