Bushwich Avenue Station
The Bay Ridge Line had a station somewhere around here on Bushwich Avenue that was closed in 1915 when the East New York Tunnel put the line under Bushwick Avenue. The Bushwich Avenue station had replaced a station at Central Avenue that was only open for a year in 1883.
After using the high platform at Broadway Junction, the BMT Canarsie Line (L train) makes a steep descent into a tunnel under Bushwick Avenue, with a subterranean station just north of Bushwick Avenue on Aberdeen Street, only a few hundred feet before both the Canarsie Line and the Bay Ridge Line emerge from their tunnel. The lines run parallel and fairly close to each other under the Rudd Playground at this point and the land directly over the tunnels is an undeveloped wooded area until the tracks emerge from the tunnel to the northwest.
If the Circumferential Line and the Canarsie Line are sharing tracks from the south and choose to use the existing high platform at Broadway Junction, there would be no need for any significant changes here. However, if they use the East New York tunnel, new platforms and, likely, excavation would be needed unless there's a way to crossover between the Bay Ridge Line tunnel and Canarsie Line tunnel prior to the Bushwick Avenue station.
Next: Bushwick, Brooklyn