Bryan Blake submitted the route:
A 100K (62 mile) single-loop road route encompassing all 50 US state-named streets within Washington, DC. Link to route map is here:
This route was set up as a bike route [with annual group rides put on by the Washington Area Bicycle Association] but to my knowledge has not been attempted as a single run; any claim/credit for the route creation should go to the user at the route link via mapmyrun.com.
[Note there is also a Strava Club for the ride.]