Here in Canada, and US also I believe with a couple states holding exception, three wheelers can't be road legal..
It's purely a matter of classification..even if you were to equip them with lights and whatever other items needed for road compliance, they just simply are classed as 'off-road use only' and can't be registered as a road vehicle..
In fact in Ontario they don't even classify as ATVs which at least have limited road privledges in some municipalities..I ride every spring in northern Ontario. I have to keep insurance, plated and paperwork to attend the event. During the event there are sections where we have to run on gravel roads to get from one trail head to another..almost every time we go there are police there ensuring that no one is drinking and whatnot.
Anyway they always stop us on the road section and give us the speech about the legal issue with trikes on the road..but then they let us pass anyway. If we weren't part of a sanctioned event we'd likely get fined!!
Current toys..
1986 Honda 350X..trail bomb!
1985 Honda 250SX..my main mudder
1985 Honda 250ES..Back in Black Trike
Current non-trike toys:
1990 Honda TRX300FW
1995 Seadoo GTX
1998 Polaris Indy Lite 340(Nearly new looking)
1998 Polaris Touring 500
1998 Club Car (electric)