RCW 46.04.330: Motorcycle.

"Motorcycle" means a motor vehicle designed to travel on not more than three wheels, not including any stabilizing conversion kits, on which the driver: (1) Rides on a seat or saddle and the motor vehicle is designed to be steered with a handlebar; or (2) Rides on a seat in a partially or completely enclosed seating area that is equipped with safety belts and the motor vehicle is designed to be steered with a steering wheel. "Motorcycle" excludes a farm tractor, a power wheelchair, an electric personal assistive mobility device, a motorized foot scooter, an electric-assisted bicycle, and a moped.