The above map, made by Eric Fischer at Mapbox using federal data, shows in yellow every road in the country, from Interstates to local arterials, that’s part of the Federal-Aid Highway Program. This is the road infrastructure that’s supported by the Highway Trust Fund and, in short, your gas taxes.
Zoom in, and Fischer has mapped each road by how heavily it’s used. The 14th Street Bridge connecting Washington and Virginia, for instance, saw on average more than 175,000 cars traveling across all of its lanes in both directions each day in 2012 (the thickness of each yellow line corresponds to the heaviness of its traffic flow):
