The population density of the D.C. region has gone up but also spread farther out during the past half-century, according to a recent analysis of U.S. Census Bureau data by a local think tank. The D.C. Policy Center (DCPC) reports that between 1970 and 2010, the last decennial census year, residential areas continued to expand at a remove from the District’s downtown.
“[I]nner suburban densities did increase, though rarely to levels where car-dependence breaks down,” DCPC fellow D.W. Rowlands writes of the changes. “However, the lower-density inner suburbs were replaced by a rapidly growing swath of low-density suburbs further and further outside the Beltway.” Up until 2010, the Mid-City, Capitol Hill, and easternmost parts of the District lost population density, seeing a “hollowing-out effect.”
The creation of the Metro system, starting in the 1970s, helps explain this pattern of growth, but so does the layout of major regional roads. According to Rowlands, D.C.’s suburbs “grew outward in every direction, though particularly to the north (along the I-270 corridor) and to the west (along the Dulles Toll Road, I-66, and I[-]95).” Still, by 1970, many people resided outside the city: “Nearly every census tract within the Beltway had a substantial population.”
The measure of population density in DCPC’s analysis ranges in bands from 0 to 1.5 people per acre to more than 30 people per acre. Public transit becomes a more common mode of transportation once there are at least 15 people per acre living in an area, explains the study.