[wheels]

> if you live in a dense city with poor traffic flow, and that accounts for a tiny percentage of the world population

That's false. Most of the world's population now lives in cities. Deciding what percentage of those fall below the threshold of "poor" traffic-flow wise is difficult, but it's not "tiny". (http://www.gizmag.com/go/7613/)

Cars beget cars. The reason people need cars in a lot of the US is because they moved somewhere that they need a car to get to. People talk about the amount of time that things take without a car forgetting that said problem was created by cars in the first place. In places where most folks don't have cars you have a small grocery store every few blocks rather than a large one every few miles. The demographics of public transit differ from society at large because the well-off drive cars.

I grew up in American suburbia and have lived in Europe for the last decade. The amount of time required to say, go shopping, or commute to work has remained broadly similar in the half-dozen areas I've lived in, though the distances have not.

Progressively moving away from cars is largely a cultural rather than technological problem. Some well-done urban planning (including structuring energy prices to favor more efficient means) and a few decades to execute it could drastically shift the balance to where we have far fewer cars.

[kstenerud]

The generic "city" is not a very useful term here. How many people are there? There's a big difference between New York and Maza. What is the topography like? Is it sprawling like Phoenix? Or dense like Tokyo? How much density, population, and infrastructure is required to make a convenient and economical transit system? I'd wager far too much to displace cars in any meaningful way except in the largest cities.

Cars are used because they are versatile. Every other form of transport has far more narrow use cases.