Reuben Fischer-Baum | FiveThirtyEight

After decades of planning, the Washington Metro’s Silver Line finally opened last week. The line aims to make inroads in a car-centric swath of Northern Virginia, but D.C. itself is already known for its robust public transit. How robust?

Very. To receive grants from the Federal Transit Administration, transit systems of all types (heavy rail, light rail, buses, etc.) must provide monthly ridership data to the National Transit Database (NTD, data available to download here), which compiles it by census-designated urbanized areas. The measure used is “unlinked trips,” which counts transfers during the same journey as separate trips. This figure can be converted to “trips per resident” by dividing unlinked trips in 2013 by 2012 population estimates from the American Community Survey (ACS), yielding a figure that’s neatly comparable among cities of varying sizes.

The U.S. has 415 urbanized areas with populations over 65,000 — large enough to get a one-year ACS estimate — and 70 percent (290) of them reported data to the NTD in every month of 2013. The gaps are mostly small cities: The 54 largest urban areas were included in the data set, as were 93 percent of urban areas with over 200,000 residents (169 out of 182). Read more