People won't take another driving test just to get a small car.
Besides which, if you do license them as motorcycles, you have to let them take the motorcycle driving test in them. My father took his on a Harley Davidson servicar -- http://www.flickr.co...raphy/2617584638/ No, not that one. :-(
The (new) guy giving the test said he couldn't take it on that. Dad asked, "So I'm allowed to drive it on the street without a motorcycle certification or a helmet?" Umm, no? "Then it's a motorcycle."
The test had a step where you have to bring it to a complete stop and start again without putting your feet down. Dad stopped, looked at the guy and said, "Is that fully stopped? I'm not quite sure. How about now?"
The older guys were standing inside watching through the front window laughing their asses off.