This comes up every couple of years or so. For a really long read on what happened to Dave Lemon (sp?) of Mazdatrix fame head over to the prodcar board and do a search.

To make a long story short, the state DOT in Arizona (or was it California?) has decided that club racers are racing for 'gain', in that they might win a plastic trophy and the end of the day, and are thus commercial haulers. IIRC, they effectively impounded his rig until he could hire a CDL driver to drive it to the state line for him.

None of this applies, of course, to grandpa and grandma driving their 45,000 lb bus conversion motorhome with air brakes flat towing a jeep liberty at 55 in the passing lane.