In Governing magazine, William Fulton raises a consequence of compact urban areas that I had not realized fully. Even if a place is car dependent -- public transit is inadequate for its residents needs -- it can still reduce traffic if the people who live there don't have to drive as far because everything is relatively close together. Compact urban areas reduce traffic simply by being compact.
Which brings us to proximity. One of the few ways around this problem is to build more housing close to the urban cores -- or, at least, close to the dense suburban job centers. Urban planners often argue for locating more housing along high-frequency transit lines, which makes sense because many people can commute by transit.
What’s not well understood, however, is that well-located housing can cut down on the amount of driving -- and hence the need for additional road space -- even if people are still tethered to their cars. One famous study in the San Francisco Bay Area found that people living in Berkeley and Oakland drive only half as far as people in the outer suburbs -- not because they take transit more, but because the places they have to go are closer together.