Years ago I stopped and gave a Goldwing rider on an add on "Trike Kit" a lift after a Trooper pulled him over. What happened during the talk with the Trooper I do not know, just that He was pulled over in the HOV lane for speeding and being a single occupant on a 4 wheel vehicle. They impounded his bike. I have to assume he got lippy with the Trooper, That's an automatic "Your a NO-GO at this station, Move on.
In Washington state it says, a motorcycle is two or three tires in contact with the road. Not the same rules in all states so contact your local DMV or DOL. We have had these topics pop up and sometimes arguments start over reading (or reading only what you want it to say) the local laws/Reg's. Check your own area. I do not have the current Washington State Regulation on hand but I do have a matrix. It does not have 4 wheels listed.