A few weeks ago, the Antiplanner posted commuting data from the Census Bureau’s 2015 American Community Survey. But I haven’t compared commuting with urban densities since the 2000 census. The chart below shows this comparison for 226 urbanized areas.
For each decennial census, the Census Bureau maps the land around each major city that is urbanized. The agency’s definition of “urban” is lengthy, but basically it is about 1,000 people per square mile, or 500 people per square mile if the land around them is developed for urban but non-residential purposes. The agency does not remap areas between decennial censuses, so I used the 2010 boundaries to calculate both population density and how people get to work in 2015.
The charts for 2015 and 2000 are not all that different. Both show a trend line indicating that density has to increase by several hundred percent to reduce the share of people commuting by car by 10 percent. Thus, increasing densities to reducing driving is not a very promising strategy.
Of course, commuting is only a small portion of total driving. But it is also the portion that transit is most likely to attract, so the automobile’s share of total urban travel is greater than shown in the charts.