No form of transportation has any privilege under the Constitution.
Yeah, because it's obviously a right, and the Constitution grants no power for Congress to abridge that right.
The primary argument against a "bill of rights" among our Founding Fathers was precisely that by enumerating rights, other plain & obvious rights would be discounted as such because they were not enumerated therein. The right of travel, including vehicular travel, was so blatantly obvious and unassailable that the Founding Fathers felt no need to consume space & rhetoric listing it among other rights which were more immediately & continually endangered. It never occurred to them that such a right would even need explicit recognition & protection. Can YOU imagine George Washington saying "why yes, the federal government CAN impose extensive convoluted restrictions on who can travel how by what vehicles"? of course not, he'd look at you with a "what the he11 is wrong with you" expression at the suggestion that vehicular travel is not a right.