Thanks Rassy, I''m glad to hear you think it should work to use one throttle.
I live in California, where a bicycle can have any number of wheels:
Defines bicycle as a device upon which any person may ride, propelled exclusively by human power through a belt, chain, or gears and having one or more wheels. Specifically provides that persons riding bicycles are subject to Vehicle Code provisions specified in Sections 21200 and 21200.5
And a motorized bicycle can either have 2 to 3 wheels and go up to 30mph (and produce 2HP or less) and not need pedals,
OR it can have more than 3 wheels, but then it may only go up to 20mph (and produce 1000w or less) and must have pedals:http://www.dmv.ca.gov/pubs/vctop/d01/vc406.htm
Thanks for the word of caution. I think if I lived in a place where this was not the case, I would try riding one anyway.
Safety laws are usually enforced when there is an obvious danger, and those laws were written before quads were available, so in the unlikely event of a ticket, if I didn't want to just pay it, I might argue that the law is outdated and not intended to be construed to ban quads. They tip less easily than trikes, so if trikes are ok, there really is no argument to punish quad owners.