People can bicycle at 20mph too using their legs. On paths and lanes where these things are banned.
Common sense wattage restrictions (I have seen 1hp or 750W as a threshold, for example, and apparently parts of Europe do 250W limits) are perfectly feasible.
Apparently federal law on imports dictates that the class of 'low-speed electric bicycles' is defined by a maximum of 750W and 20mph, which is a surprisingly appropriate envelope - about as much as you'd want out of a single-rider passenger bicycle with a heavy rider or cargo in a hilly city.
That's part of the EU recommendation for classification as an assisted bicycle (pedelec) rather than an electric moped (e-bike): 250W maximum continuous rated power, assistance-only (user must be pedalling for engine to engage) and progressive cutoff to 25km/h[0] (so the cutoff starts earlier, at 25km/h or above there's no assistance)
Common sense wattage restrictions (I have seen 1hp or 750W as a threshold, for example, and apparently parts of Europe do 250W limits) are perfectly feasible.
Apparently federal law on imports dictates that the class of 'low-speed electric bicycles' is defined by a maximum of 750W and 20mph, which is a surprisingly appropriate envelope - about as much as you'd want out of a single-rider passenger bicycle with a heavy rider or cargo in a hilly city.
* https://en.wikipedia.org/wiki/Electric_bicycle_laws#Defined
* http://www.alysion.org/ebiketours/power.html