In 1966 when Metro planners were considering how to cross Rock Creek, one proposal suggested adding new tracks to the bottom of the Taft Bridge.

Metro Taft Bridge proposal. Image originally from WMATA, copied from Ghosts of DC.

Rock Creek presented a big problem to Metrorail. Or rather, not so much the creek itself as the deep canyon-like gulch it runs through. To cross the gulch, Metro’s subway tunnels must drop deep underground, much further than normal. Bridging over Rock Creek would’ve meant shallower tunnels on either end, and less expensive, easier to build stations at Dupont Circle and Woodley Park.

Obviously the bridge idea near happened. Metro stayed underground through the whole area, which is why Dupont and Woodley stations are as deep as they are.

For more on this interesting idea, including additional renderings of alternate designs, check out Ghosts of DC.