Those aren’t bridges — they’re graphs of how many people enter and exit each Metro station for each quarter of an hour. Reddit user BioNrd created the image using Metro’s October 2014 data, which the agency recently made available.

Click on the image to see the full version.

The darker dots are entries, the gray ones exits. You can see the stations with the greatest traffic are the ones with the dark peak in the afternoon (stations generally downtown). What else do you notice?

David Alpert is Founder and President of Greater Greater Washington and Executive Director of DC Sustainable Transportation (DCST). He worked as a Product Manager for Google for six years and has lived in the Boston, San Francisco, and New York metro areas in addition to Washington, DC. He lives with his wife and two children in Dupont Circle. Unless otherwise noted, opinions in his GGWash posts are his and not the official views of GGWash or DCST.