[dwallin]

Urban density doesn't cause the issue of traffic. The issue of traffic is caused by cars. Urban density allows public transportation, the only current viable alternative, to be financially sound on a large scale.

[hamandcheese]

business density - important difference from density in general.

Take San Francisco, for example. We have transit. But riding at peak hours sucks and will always suck because everyone is going to the same place.

Concentration of offices downtown makes transit to anywhere else less viable - hence the only subway in SF goes to one place.