These would be great for city travel. The two main issues would be safety and parking. They'd have to make a strong case for the vehicle being safe in the case of an accident, not unlike the challenge the Smart Car had. For the issue of parking it would be unlikely that a city would set aside real estate just for these cars as they'd have to do it all over the city and it would be relatively expensive. I think a better solution would be a car-sharing one like Zip Cars. I can pay a monthly fee to have access to the cars at certain spots and if I want to leave in rush hour, I'd pay a premium, or something to that extent. It's a really interesting idea, I live in NYC and I'd love it here.