The Concourse Line begins as a two-track line at Norwood – 205th Street. As it travels west, a center track forms which leads to the Concourse Yard. The line then curves south to the Grand Concourse, from which it derives its name. Two tracks from the Concourse Yard arrive between the two revenue tracks with switches and diamond crossovers between all four of them before the yard tracks merge to form the center track at Bedford Park Boulevard.
Passing over 175th Street
South of this station, the two outer tracks merge into a single center express track while the center track splits to become the local tracks. The line then runs south with diamond crossovers at Tremont Avenue. Due to the terrain, the vicinity of 174th–175th Street station is uniquely built both underground and over 175th Street. Between 170th Street and 167th Street are more switches and crossovers, with a lay-up track adjacent to the Manhattan-bound local track.
On December 15, 1940, with the opening of the IND Sixth Avenue Line, the D train began serving the IND Concourse Line with the C and CC. It made express stops in peak during rush hours and Saturdays and local stops at all other times. C service was discontinued in 1949-51, but reinstated in 1985 when double letters used to indicate local service was discontinued. The D made local stops along the Concourse Line at all times except rush hours, when the C ran local to Bedford Park Boulevard. On March 1, 1998, the B train replaced the C as the rush-hour local on the Concourse Line.
Except for minor maintenance work and a station rehabilitation at 161st Street – Yankee Stadium, stations on the Concourse Line have largely been untouched since its opening in 1933, except for entrance closings and other reductions in service areas.
It is of note that the line was originally intended to be four tracks, rather than three tracks, to Bedford Park Boulevard. This is the only IND line with three tracks (all other IND lines have either two or four tracks), and the 145th Street station was originally provisioned for four tracks. Additionally, the line is mostly straight north of 161st Street – Yankee Stadium, but makes a slight right turn to end at Norwood – 205th Street, with a provision to extend to Baychester Avenue and Boston Road. When the line was opened in 1933, a proposed expansion of the New York City Subway had multiple IND lines criss-crossing the five boroughs; however, the country was in the midst of the Great Depression, and the city had neither the money nor the need to either extend the line east of 205th Street or make the line four tracks. The city found it easier and less expensive to purchase the IRT Dyre Avenue Line, extinguishing the plans for the IND Concourse Line to extend to Baychester Avenue.
Note that this is a list of New York City Subway lines, which are the physical infrastructure over which services operate.
Lines with colors next to them are trunk lines; trunk lines determine the color of New York City Subway service bullets, except for shuttles, which are dark gray.