A Bay Ridge bound R train zips through the NYC Subway's Montague St Tunnel from Manhattan to Brooklyn. This under-river tunnel was constructed from 1914-1917 for New York's old Brooklyn Rapid Transit Company (BRT)--later known as the Brooklyn-Manhattan Transit Corporation (BMT)--to connect the Broadway Line in Manhattan to the 4th Ave Line in Brooklyn.
This interlocking (track switch) was built into these tubes under the East River on the Manhattan side, and the track the shot was taken on branches from the BMT Nassau St Line (today's J and Z line). The M train used to run down this track to connect from the Nassau St Line to the 4th Ave Line, but the route was cut in 2010 due to low demand between Nassau and 4th Ave.
This series of shots was taken handheld on a Sony a7R II, five separate shots combined into one short video. These shots individually are special to me, but I decided this animated format did them better justice. The rolling stock is R160A type.