The "rules" as far as I can make out are kinda foggy here.
A bicycle is defined basically as a human powered thing with at least 1 wheel being over 20" in size, and of course no engine of any kind, period.
But a moped is a powered thing with no specification on wheel size but with an engine no larger than 50cc and pedals to assist or whatever.
So, I would assume there is no specific "ruel/law/whatever" that pertains to adult sized bicycles with engines on them. So, I guess they'd say it's a moped, and how do they know what size the engine is? Since there is no specific law IMO pertaining to what I'm riding, I will take a chance till I get caught once and see what happens. Then figure out what to do after that.
Oh, and I will "pay the man" whatever he likes to be legal if I have to. It's worth it either way in gas savings.