The New York City Transit Authority operates a total of 24 rail yards for the New York City Subway system, and one for the Staten Island Railway. There are 10 active A Division yards and 11 active B Division yards, two of which are shared between divisions for storage and car washing. In addition, there is one yard for the Staten Island Railway and three non-revenue (Maintenance of Way, or MoW) Division-independent yards. Many of the system's yards are used for off-peak storage, whereas some have inspection facilities where basic routine maintenance is carried out. Of these yards, rolling stock are assigned to seven A Division yards and seven B Division yards. Within the yards are 14 maintenance facilities, whereas two yards (207th Street and Coney Island) perform major overhaul and car rebuilding work. A Division yards The A Division's yards consist of the 239th Street, 240th Street, Corona, East 180th Street, Jerome, Livonia, and Westchester maintenance yards, plus three other non-maintenance storage yards. A total of 2892 cars are assigned to the seven maintenance yards. 137th Street Yard The 137th Street Yard is an underground rail yard located between 145th Street and 137th Street–City College on the IRT Broadway–Seventh Avenue Line, the latter of which is the yard's namesake. The yard has five tracks surrounding the three mainline tracks, with three tracks located on the west (southbound side) and two tracks located on the east (northbound side). The yard is used to store some trains outside of rush hours. Each track can hold two full-length trains, so a total of 10 trains can be stored there at any given time. Because the tracks are on a 1% downgrade in the southbound direction, each of the layup tracks are equipped with a derail to protect the main line from a runaway train in the event a train placed on any one the storage tracks is not properly secured. 239th Street Yard The 239th Street Yard is the northernmost rail yard in the system, located at 4570 Furman Avenue in the Wakefield section of the North Bronx, and is home to the R142s assigned to the . There is also considerable fleet interoperability with the , as 5 trains are based out of the nearby East 180th Street Yard and share a similarly-sized fleet. 5 trains use the upper portion of the yard for off-peak storage. Opened in 1916, it is