Mopeds fall within NHTSA’s jurisdiction when they can go over 20 mph and are meant to be used primarily on roads. They’re considered “motor-drive cycles,” which are a subset of motorcycles. In NHTSA’s world, a motorcycle is “a motor vehicle with motive power having a seat or saddle for the use of the rider and designed to travel on not more than three wheels in contact with the ground.” A motor-drive cycle is “a motorcycle with a motor that produces 5–brake horsepower or less.” Since these mopeds are regulated by NHTSA, they cannot be imported into or sold in the United States without complying with the FMVSS.
Since NHTSA is focused on vehicles meant for road use, one might wonder whether the use of bike paths changes NHTSA’s jurisdiction over mopeds. Ultimately, though, NHTSA is focused on speed. According to NHTSA’s published interpretations of its regulations, the agency “believe[s] that vehicles with speeds of over 20 mph are capable of on-road operation,” and therefore fall within their purview. NHTSA makes classifications for vehicles in interstate commerce. The classifications are meant to be as applicable in California as they are in Tennessee or Maine. Some cities may have ample bike lanes such that it would be reasonable for the bikes to never be used on roads, but most do not. NHTSA’s classifications will not change from location to location.