For the purpose of this section, the term “low-speed electric bicycle” means a two- or three-wheeled vehicle with fully operable pedals and an electric motor of less than 750 watts (1 h.p.), whose maximum speed on a paved level surface, when powered solely by such a motor while ridden by an operator who weighs 170 pounds, is less than 20 mph.
15 U.S. Code § 2085 - Low-speed electric bicycles
(c) Promulgation of requirements
 See References in Text note below.