The BMT Sea Beach Line (N train)
also used to terminate at the 64th Street Ferry pier and when the
4th Avenue BMT (N/R train)
was built in 1915, the interconnection of the two lines allowed trains
coming from the north to fork at 66th street (just east of the Bay Ridge rail yard)
with the R train proceeding south into Bay Ridge proper and the N train headed east and
then south to Coney Island.
The BMT Sea Beach Line shares the rail ROW (on separate tracks) with the Bay Ridge Line
between 4th Avenue and 14th Avenue. Presumably, the Circumferential Line would just
use the existing BMT tracks for this portion of its run to save construction costs, although
there might be some congestion issues at rush hour.
The streets to the north of the tracks are largely devoted to commercial activity,
much of it by Chinese businesses.