In the US, something like 39% of the population lives in an urban environment with a population of 50,000 or larger. That means 61% live in smaller areas. In my city of approximately 55,000, it is hard to make do with not leaving the to go to surrounding towns and that almost always means speeds of 45-55mph.

I'm a little unclear on what cities in the US are large enough that most people wouldn't need a vehicle that can go faster (for the sake of being allowed on the needed roads), and yet would be a city where enough people would want their own car for use inside of the city instead of relying on foot/public transport.

I think that most likely a successful city car in the US would still need to be able to do a minimum of 45mph, and I could see arguments for 60mph or 70mph as the minimum instead. I could see getting away with all the driving I do in a typical month with something that couldn't do more than 45 though. 19mph is too slow for my typical week, unless it took the form of a cargo bike.