“Moped” means every motorcycle or motor-driven cycle unless otherwise specified in this chapter, which is equipped with two or three wheels, foot pedals to permit muscular propulsion, and an independent power source providing a maximum of two-brake horsepower, but excludes electric bicycles as defined in § 17C-1-70 of this code. If a combustion engine is used, the maximum piston or rotor displacement shall be 50 cubic centimeters regardless of the number of chambers in the power source. The power source shall be capable of propelling the vehicle, unassisted, at a speed not to exceed 30 miles per hour on a level road surface and shall be equipped with a power drive system that functions directly or automatically only, not requiring clutching or shifting by the operator after the drive system is engaged.