High density cities are just not feasible. The fallacy of public transportation does not solve the transportation problems that are created by separating work places, services and housing from each other.
Look at Toronto for example. The city is dead at weekends, evenings and nights. The only reason for people to go to a city is that they have to work there. Malls create services near the customers. The next step is to distribute the work so that unnecessary transportation can be eliminated.