IRT East Side Line

IRT Lexington Avenue Line
Services that use the IRT Lexington Avenue Line have been colored green since 1979. The original IRT numbering system provided for 4, 5, and 6 on the line.
Overview
Type	Rapid transit
System	New York City Subway
Status	Operational
Locale	Manhattan, New York City, NY
Termini	125th Street Bowling Green
Stations	27 (23 in use)
Daily ridership	1,289,338
Operation
Opened	1904–1918
Owner	City of New York
Operator(s)	New York City Transit Authority
Character	Underground
Technical
Number of tracks	2–4
Track gauge	1,435 mm (4 ft 8 1⁄2 in)
Electrification	600V DC third rail

The Lexington Avenue Line (also known as the East Side Line) is one of the lines of the IRT division of the New York City Subway, stretching from Downtown Brooklyn or Lower Manhattan north to 125th Street in East Harlem. The portion in Lower and Midtown Manhattan was part of the city's first subway line. The line is served by the 4 5 6 <6>  trains.

For decades, the Lexington Avenue line was the only line in Manhattan to directly serve the Upper East Side and East Midtown; this four-track line is the most used rapid transit line in the United States. Its average of 1.3 million daily riders is more than the total riderships of the transit systems of San Francisco (452,600 weekday passengers), Chicago (772,900 weekday passengers), and Boston (569,200). In 2007, its ridership also exceeded that of the entire Washington Metro, and in part spurred the construction of the parallel Second Avenue Subway that year, to relieve congestion on the Lexington Avenue line.