The real thing I would advocate (if this weren't a beautiful Sunday afternoon, calling me from my keyboard) is a design for traffic that began from the premise of three (or four) interconnected but separate networks, one each for pedestrians, bikes, and rail, and maybe one network of specialized freeways for trucks and buses. Personal cars would be a luxury (unless you live in the country) that few would need (rather than a cornerstone of our economy) with rentals taking up the slack for vacations and such.

But if you're interested in this sort of thing, don't bother with my blathering, go read Christopher Alexander.

My other answer is really just an invitation to a kind of thought experiment: what if we really did restrict ourselves to just walking, biking, and trains? How would civilization look in that alternate reality?

If decreasing your speed from 100km/h to 50km/h gives you a 1% lower chance of dying in a road traffic accident, but you spend an additional 2% of your life stuck in traffic, is that a win?