What Makes a Place Walkable?

Bikes at Work has an interesting database that uses census numbers to show how many people walk to their jobs in cities, towns and villages across the US. A quick search for the highest walk-to-work locations for towns with over 1000 people yields the following results:

Location POP % Walk to work
Naval Academy, Maryland 4264 82.99%
Houghton, New York 1730 67.84%
Alfred village, New York 3926 60.98%
West Point, New York 7138 60.25%
Air Force Academy, Colorado 7536 59.63%
Parris Island, South Carolina 4841 58.45%
Lackland AFB CDP, Texas 7132 58.09%
New Square village, New York 4707 57.28%
Hamilton village, New York 3510 55.56%
Avalon city, California 3181 52.79

Almost all of these are centered around an institution, like a university or military academy, where many are housed very close to their classes or jobs. The concentration of people and buildings reduces the amount of space that could be used for roads and parking. Raising the threshold to at least 20,000 residents:

Location POP % Walk to work
Ithaca city, New York 29006 43.33%
Athens city, Ohio 21192 42.39%
State College, Pennsylvania 38420 41.8%
North Chicago, Illinois 36001 29.06%
Oxford city, Ohio 22087 28.86%
Fort Bragg, North Carolina 29246 26.13%
Cambridge, Massachusetts 101355 25.76%
Fort Hood, Texas 33595 23.87%
College Park, Maryland 24590 23.28%
Pullman city, Washington 24740 22.53%

Again, with few exceptions, we find the pattern of high walking rates and major institutions of higher learning, military bases and areas of mixed use development. Now, setting the bar at over 250,000 residents:

Location POP % Walk to work
Boston, Massachusetts 589141 13.36%
Washington, DC 572059 12.27%
New York City, New York 8008278 10.72%
Pittsburgh, Pennsylvania 334563 10.02%
San Francisco, California 776733 9.82%
Philadelphia, Pennsylvania 1517550 9.22%
Newark, New Jersey 273546 8.03%
Seattle, Washington 563375 7.72%
Baltimore, Maryland 651154 7.28%
Minneapolis, Minnesota 382452 6.85%

While all of these cities have colleges and universities and other major institutions, they are part of a very large mix and cannot alone account for why these cities are on the list. Even controlling for population density does not account for this distribution. These are cities that grew to sizable populations before the automobile, which may explain why they are on this list instead of Los Angeles, Phoenix, Atlanta, Houston and Dallas. Surprising in their absence, meanwhile, are Chicago and Portland. They aren't that far off, but while both cities receive a lot of credit for their green initiatives they don't seem to encourage walking to work as much as the cities above.

An even better measure of walkability than the percentage that walk to work would be the number that walk to the grocery store or pharmacy. Walkscore as a defining metric for such an assessment has its flaws, but is generally useful. Looking at both the Bikes at Work census analysis and Walkscore, it would seem that there are two major factors that influence the walkability of a city or town: institutional presence and pre-auto urban design.

The key to both appears to be co-location of housing with the various destinations that people need and desire. But there is a choice here that seems worth considering in greater depth. If we want to create a post-carbon society, creating more walkable communities seems like a major priority. But what kind of walking towns do we want?