It's called electric assist
We don't have it here partly because if anyone did, they would be able to undercut the rest of us. I think some of the London rickshaws do, and in Amsterdam too.

There's a story that a London rickshaw cyclist, used to flat roads and electric assist, came up here to work a few years ago. After one night, he quit over the phone from the train back to London.
( MatJ LOOK, Wed 22 May 2013, 18:37, Reply)