Car size should be regulated and a maximum should be enforced. Pavement parking (and other antisocial forms of parking) should also be banned. In the UK, local authorities are in charge of parking enforcement. In Oxford they largely don't bother: I see vehicles parked on yellow lines every day. I can't fathom why, this is an opportunity to raise revenue!
I feel that all those people who talk about reducing car size and use probably don’t have a family. I have twin 6 month olds and the only cars we currently use is the Toyota Corolla from a local car sharing service. Two car seats in the back leave basically just enough room between for my wife to fit sideways inside the middle seat. She can’t stay in there for longer than a few minutes and if we get in a car accident…
Compared to most large East and Southeast Asian cities (Shanghai, Tokyo, Seoul, Hong Kong, Singapore), public transport in American cities is generally lousy, especially if a 15-minute drive (that's about 10 – 15km, maybe) turns into a multiple-hour affair. At that rate, one might as well walk.