Here in michigan I think you can make them legal as well, that is if they go under a motorcycle license, or how ever a trike gets legal for the road. Requirements are something like..
DOT approved tires for the road
Front/Rear lights
Brake lights
Parking brake
Mirror(s)
Turn signals can be done with hand signals
I'm like 80% sure you have to re title it for on road use, and it has to be inspected by an officer.