"Electric personal assistive mobility device" or "EPAMD" means a self-balancing, two nontandem-wheeled device, designed to transport only one person, with an electric propulsion system with average power of seven hundred fifty watts (one horse power), whose maximum speed on a paved level surface, when powered solely by such a propulsion system while ridden by an operator who weighs one hundred seventy pounds, is less than twenty miles per hour.