Yeah, the skateboard-to-bike range of mobility tools is just lovely in the city -- they have the property that you can go much faster than walking with far less effort, but you can also carry your transportation (up stairs, over obstacles, etc.) With a car, if you run into a traffic jam or an obstacle or a mechanical failure, you're screwed.

Bikes are definitely on the big end, being things that not everyone can carry, and that definitely can't just be strapped onto your back. (But they do let you carry cargo.)