> Light rail is incredibly efficient, and in a system where you are designing the city first, I'd forgo roads entirely.

While I'm a firm believer that private cars (at least at a scale seen in the U.S.) and dense cities are fundamentally incompatible, I'm not quite onboard with getting rid of roads altogether. What about bicycles? Emergency vehicles? Construction equipment? Furniture deliveries? Deliveries of merchandise to stores? None of these things are going to be able to get around without a road network of some description, albeit hopefully one significantly reduced in scope from a typical American city.