These arches are part of the Department of Agriculture in Washington, D.C. This shot was taken from 14th SW Street, close to the U.S. Holocaust Museum.
This shot is taken from the opposite end (12th SW Street). The arches are one block away from the National Mall.
Washington D.C. could use some pedestrian bridges, with all the traffic and the many pedestrians. But nothing this big for pedestrians, please.
For more bridges, visit the Sunday Bridge Series:
Update: more on the bridges between the buildings on Wikipedia