Read other letters about this article
1) It'd be somewhere slightly above 30, in my experience; of course, literally, YMMV.
2) I think it'd be fine on a major throughway. I'd feel safe.
3) It could be *my* only car, sure. I think it could be the only car for many in SF and NYC and DC and Seattle and perhaps other cities. Remember that if it doesn't quite satisfy all your needs -- if you want a bigger car for occasional outdoorsy jaunts -- you can always rent a temporary one from one of the many car-sharing services popping up. But again, as you note, it's not for everyone.