The bridge noelbotevera is referring to carried two-way traffic prior to that area's reconfiguration after the Roosevelt Bridge opened. If you don't zoom the 1964 Historic Aerials image in, you can see how US-50 went eastbound across that bridge and then curved to the south, joining what is now the ramp that carries traffic from Memorial Bridge towards I-395 and the southbound GW Parkway. The road passed under Memorial Avenue (the road connecting the circle to the cemetery) and then curved around to the left via a ramp that no longer exists to access the circle and the bridge. Traffic coming south on the GW Parkway used a loop ramp adjacent to the bridge noelbotevera mentions in order to connect to that bridge and then continue southbound.
Once the Roosevelt Bridge opened and US-50 traffic shifted to that route, the area was reconfigured. The loop ramp was eliminated, as was two-way traffic on the bridge in question. Instead, eastbound traffic was funnelled to the realigned GW Parkway via a new ramp (the stub of which is visible in the 1964 Historic Aerials image), and then another new ramp that uses a sort of U-turn layout (except it's on the right) was constructed to connect the GW Parkway to Memorial Avenue. Traffic heading from the Parkway to either the bridge or the cemetery still uses that ramp, goes through the annoying stop sign at its end, and turns right (for the bridge) or left (for the cemetery). You could also use the latter option to connect to Route 110 if you wanted to go from the GW Parkway to Crystal City, although there are better ways to make that movement that avoid the stop sign and the 15-mph zone with heavy pedestrian traffic on Memorial Avenue. As noelbotevera notes, the southbound GW Parkway was realigned through Virginia and now crosses Boundary Channel south of the area in question.
Both of the U-shaped ramps on Columbia Island are now gone. The northern one closed sometime within the past year as part of various reconfiguration efforts intended to reduce the number of crashes and improve pedestrian safety (the latter a well-intentioned effort that likely won't work as well as they hope).