Park-242nd Street and 238th Street. This yard holds 21 layup tracks and can hold the entire rolling stock for the 1. The next yard, 207th Street Yard holds a few trains that are used during rush hours and cleans and overhauls some of the line's fleet. Finally, the 137th Street Yard has six tracks, which hold rush hour turn-around trains. Where the Brooklyn Branch ends at its southern end is unclear. In a 1981 list of "most deteriorated subway stations", the MTA listed Borough Hall and Clark Street stations as part of the IRT New Lots Line. However, as of 2007, emergency exit signs label Borough Hall as an IRT Broadway–Seventh Avenue Line station, and the two parts of Borough Hall are signed as being along the Broadway–Seventh Avenue and IRT Eastern Parkway Lines. At Borough Hall, the chaining designations, "K" (Clark Street Tunnel) and "M" (Joralemon Street Tunnel), which are used to precisely specify locations in the system, join and become "E" (Eastern Parkway Line) at Borough Hall. Clark Street Tunnel The Clark Street Tunnel carries the under the East River between the boroughs of Manhattan and Brooklyn. It was opened for revenue service on Tuesday, April 15, 1919, relieving crowding on the Joralemon Street Tunnel and providing passengers with a direct route between Brooklyn and the west side of Manhattan. It is about long, with about underwater. Construction of the tunnel began on October 12, 1914, using a tunneling shield in conjunction with compressed air. The tunnel was designed by civil engineer Clifford Milburn Holland, who later served as the first chief engineer of the Holland Tunnel. The north tube was holed through on November 28, 1916. On December 28, 1990, an electrical fire in the Clark Street Tunnel trapped passengers on a subway train for over half an hour, killed two people, and injured 149 passengers. History Contracts 1 and 2 Operation of the first subway began on October 27, 1904, with the opening of all stations from City Hall to 145th Street on the West Side Branch. The line was mostly underground, except for the section surrounding 125th Street, which ran across the elevated Manhattan Valley Viaduct to cross a deep valley there. Service was extended to 157th Street on November 12, 1904, as that station's opening had been delayed because of painting and plastering work. The West Side Branch was extended northward to a temporary