The line begins as the two tracks of the Montague Street tunnel enter Brooklyn, coming from either the BMT Broadway Line Whitehall Street–South Ferry or the BMT Nassau Street Line Broad Street stations in Manhattan. It runs under Montague Street, through the Court Street station to Court Street where it curves slightly south through the Brooklyn Civic Center onto Willoughby Street, then through the Lawrence Street station to the point where Willoughby Street meets Flatbush Avenue Extension. There, it turns immediately into the DeKalb Avenue station under Flatbush. Here, it is joined by the four tracks coming from the Manhattan Bridge in a six-track station shared with the Brighton Line. Beyond the DeKalb station, it becomes a four-track system; it briefly turns east under Fulton Street before turning south under 4th Avenue.
Coming south from the DeKalb Avenue station and off of Fulton Street, this four-track system runs entirely under 4th Avenue to just past the 59th Street station.
Much of the surface of this segment of 4th Avenue runs at the foot of what amounts to a cliff whose rise starts in the vicinity of Union Street and does not fully ease down until about 65th Street. Certain of the streets leading up to 5th Avenue are very steep, reminding one more of what you see in San Francisco than anything you could imagine elsewhere in Brooklyn or Queens. This segment of 4th Avenue is also exceptionally wide by New York City standards, particularly considering how long ago it was laid out.
South of the 59th Street station, the line reduces to two tracks. It continues running under Fourth Avenue to its terminus at the 95th Street station. On the surface, while still wide, Fourth Avenue is obviously narrower than the section north of Leif Erickson Park.
While this section of the line currently has two tracks, there were provisions to add two additional express tracks between 59th and 85th Streets if the need should ever arise:
The subway is carried in the lower deck of a bridge over the LIRR Bay Ridge branch cut, and here it can be seen that the bridge has four trackways of which only the western two are used. The tunnel leading up to each side of the bridge was built only for the existing two tracks. At Bay Ridge Ave. and 77th St. stations, the southbound platform has the usual columns, but the northbound, being where a trackway would be if expanded, does not. At 86th St, the southbound track swings out around the platform, but the northbound is straight (from the north); in other words, this would be the western half of an express station.
Just south of the 36th Street station, the West End Line (i.e., the New Utrecht Avenue elevated line) branches off eastwards, running to its terminus at Coney Island. Until the mid-1950s, the BMT Culver Line also branched off from here.
Just beyond the 59th Street station, the Sea Beach Line branches off eastwards towards Coney Island via an open-cut right-of-way.
The Fourth Avenue Line traditionally carries the (local), (Sea Beach express) and (West End express) services. The M train operates as a local to 36th street and then on to the Bay Parkway station via the West End Line during rush hours.
The D and N trains function on the express tracks, while the local tracks carry the R. Manhattan-wards from the DeKalb Avenue station, the local tracks run to Manhattan via the Montague Street tunnel towards either the BMT Broadway Line Whitehall Street–South Ferry station or the Nassau Street Line Broad Street station. The express tracks go to Manhattan via the Manhattan Bridge, to either the BMT Broadway Line Canal Street express station and thence uptown via Broadway or to the IND Grand Street station and uptown as part of the Sixth Avenue Subway.
The Fourth Avenue Line was part of the Dual Contracts.
It replaced the parallel elements of the old, now long-ago-demolished elevated system running above 5th Avenue and 3rd Avenue, and captured the BMT lines to the east of them.
Formerly, the Fourth Avenue Line serviced the BMT Culver Line, it connecting into the 36th Street station via the BMT yards south of Greenwood Cemetery, from a now-demolished elevated structure, the barest stub of which should still be visible at the Ditmas Avenue station (even the right-of-way is gone, replaced by 80s-era houses).
|Station||Tracks||Services||Opened||Transfers and notes|
|Montague Street Tunnel branch ()|
|Court Street||local||March 11, 1920|| (IRT Broadway–Seventh Avenue Line at Borough Hall)|
(IRT Eastern Parkway Line at Borough Hall)
|Lawrence Street–MetroTech||local||March 11, 1920||See note below.|
|Manhattan Bridge branch ()|
|Myrtle Avenue||local||June 19, 1915||Closed 1956; only Manhattan-bound platform remains|
|Tunnel and Bridge tracks merge ()|
|DeKalb Avenue||all||September 13, 1915|
|local tracks split to BMT Brighton Line ()|
|Atlantic Avenue–Pacific Street||all||September 13, 1915|| (IRT Eastern Parkway Line)|
(BMT Brighton Line)
LIRR at Flatbush Avenue
|Union Street||local||September 13, 1915|
|Ninth Street||local||September 13, 1915||(BMT Culver Line at Fourth Avenue)|
|Prospect Avenue||local||September 13, 1915|
|25th Street||local||September 13, 1915|
|36th Street||all||September 13, 1915|
|track connection with BMT West End Line ()|
|45th Street||local||September 13, 1915|
|53rd Street||local||September 13, 1915|
|59th Street||all||September 13, 1915|
|express tracks split to BMT Sea Beach Line ()|
|Bay Ridge Avenue||local||September 13, 1915|
|77th Street||local||April 14, 1916|
|86th Street||local||April 14, 1916|
|Bay Ridge–95th Street||local||October 27, 1925|
Note: A direct transfer from the Lawrence Street–MetroTech station to the Jay Street–Borough Hall IND station is planned as part of the Metropolitan Transportation Authority's 2005–2009 Capital Program. This station is also where the "money train" for the IRT and BMT divisions deposit their collections, just beyond the western end of the station; the IND division does this upstairs in the Jay Street station.