Original subway

Construction started on the first IRT line in 1900.^[12] A 1902 explosion during construction seriously damaged properties just above the line.^[13] The part of the line from City Hall to just south of 42nd Street was part of the original IRT line, opened on October 27, 1904.^[14] A 0.3 miles (0.48 km) extension to Fulton Street opened at 12:01 a.m. on January 16, 1905.^[15] Only the northbound platform opened at this time.^[16][17] The next station, Wall Street, was opened on June 12, 1905, as well as the southbound platform at Fulton Street.^[18][19][20]

The first revenue train on the South Ferry extension left South Ferry at 11:59 p.m. on July 9, 1905; the extension of the IRT White Plains Road Line to West Farms opened just after.^[21] The first train ran through the Joralemon Street Tunnel to Brooklyn about 12:45 a.m. on January 9, 1908.^[22]

Dual Contracts

The original plan for what became the extension north of 42nd Street was to continue it south through Irving Place and into what is now the BMT Broadway Line at Ninth Street and Broadway. Contracts awarded on July 21, 1911, included Section 6 between 26th Street and 40th Street; at the time, the IRT had withdrawn from the talks, and the Brooklyn Rapid Transit Company (BRT) was to operate on Lexington Avenue. The IRT submitted an offer for what became its portion of the Dual Contracts on February 27, 1912,^[23] and construction was soon halted on Section 6.^[24]

The construction of this line, in conjunction with the construction of the Broadway–Seventh Avenue Line, would change the operations of the IRT system. Instead of having trains go via Park Avenue, turning onto 42nd Street, before finally turning onto Broadway, there would be two trunk lines connected by the 42nd Street Shuttle. The system would be changed from looking like a "Z" system (as seen on a map) to an H-shaped system. One trunk would run via the new Lexington Avenue Line down Park Avenue, and the other trunk would run via the new Seventh Avenue Line up Broadway.^[25] It was predicted that the subway extension would lead to the growth of the Upper East Side and the Bronx.^[26][27]

The rest of the line, north to 125th Street, opened on July 17, 1918.^[28] However, until the evening of August 1, 1918, it ran as a shuttle on the local tracks only, terminating at 42nd Street and at 167th Street on the IRT Jerome Avenue Line (where the connection from the elevated IRT Ninth Avenue Line merged). On August 1, service patterns were changed, and the Lexington Avenue Line became a through route. The IRT Broadway–Seventh Avenue Line also switched from shuttle operation at that time, and the IRT 42nd Street Shuttle was formed along the old connection between the sides. Due to the shape of the system, it was referred to as the "H system". The first section of the IRT Pelham Line also opened to Third Avenue–138th Street on August 1, 1918.^[29] The cost of the extension from Grand Central was $58 million.^[30]

The construction and opening of the Lexington Avenue Line north of Grand Central resulted in the construction of expensive apartments along Park Avenue, Madison Avenue, and Lexington Avenue.^[10]

Improvements

In 1928, the New York City Board of Transportation proposed to extend platforms at all stations between Brooklyn Bridge and Grand Central, except for 33rd Street.^[31]

On April 13, 1948, the platform extensions to accommodate ten-car trains at 23rd Street, 28th Street, and 33rd Street were opened for use.^[32] In 1949, the southbound platforms at Astor Place, Bleecker Street, Spring Street, Canal Street, and Worth Street were extended.

In 1957, the New York City Transit Authority started work on a $138 million modernization program for the Lexington Avenue Line to improve and speed up service. As part of the project, platforms on the line were extended, express platforms were built at 59th Street, additional entrances were constructed at some stations, and the line's signal system and interlockings were modernized.^[33]

Work on the reconstruction of the Brooklyn Bridge station started on May 18, 1959, and continued without interruption until it was completed on September 1, 1962. Prior to the rebuild, the station's local platform could only accommodate four cars, resulting in delays. The uptown platform's extension opened at this time (the downtown platform was lengthened in 1961) as the platforms were lengthened, widened, and straightened. Originally, the island platforms narrowed at their northern ends to an unsafe width of only five feet. The project remedied this situation, lengthening the platforms from 295 feet (90 m) to 523 feet (159 m) and widening them. The platforms were extended northward by 220 feet (67 m) to just south of Reade Street. In addition, a new exit was provided at Reade Street and Lafayette Street and a new passageway under Reade Street was built connecting to the Chambers Street station on the BMT Nassau Street Line. At the center of the enlarged platforms, a new overhead passage was built, providing more direct access to the Municipal Building.^[34] The platform extensions allowed the old platform extensions at the southern end of the station, which were used for express service, to be abandoned. These platform extensions had necessitated the use of gap fillers. This project cost $6 million, and allowed 6 trains to be lengthened to nine cars, and allowed express trains to open all doors at the station (previously the doors only opened in eight of the ten cars). Upon its completion, the Worth Street station to the north was closed due to its close proximity to the platform extensions, and, as such, the station was renamed Brooklyn Bridge–Worth Street.^[35]

In late 1959, contracts were awarded to extend the platforms at Bowling Green, Wall Street, Fulton Street, Canal Street, Spring Street, Bleecker Street, Astor Place, Grand Central, 86th Street and 125th Street to 525 feet (160 m) to accommodate ten-car trains. At the same time, work to modernize the signals and interlockings between Wall Street and 86th Street was underway.^[34] Another element of the modernization plan was the construction of a new station entrance and control building in Bowling Green Park at Bowling Green, with new stairways to the platform.^[34][33]

On July 23, 1959, the Board of Estimate approved the contract for the construction of express platforms at Lexington Avenue–59th Street. The new platforms were intended to reduce transfer congestion at Grand Central–42nd Street, and to allow transfers between the express trains and BMT trains to Queens. Even before the express platforms were added, this station was the busiest on the line.^[36][37] Construction for the express station began on August 10, 1959. The two express platforms were 14 feet (4.3 m) wide and 525 feet (160 m) long.^[34] Along with the new express platforms, a new mezzanine was built above it to connect it to the local station, and the Broadway Line station. Two high speed escalators were added to connect the local and express platforms. Two additional high speed escalators were built to connect the local platforms with the new mezzanine. As part of the plan, the local platforms were extended to accommodate 10-car trains. In addition, new entrances and booths were added to the 59th Street ends of the northbound and southbound sides. The project cost $6.5 million and was completed three months prior than originally planned when the new platforms opened on November 15, 1962.^[38]

In April 1960, work began on a $3,509,000 project to lengthen platforms on the line to accommodate ten-car trains at seven stations on the line. As part of the project, the northbound platforms at Canal Street, Spring Street, Bleecker Street, and Astor Place were lengthened from 225 feet (69 m) to 525 feet (160 m). The platform extensions at these four stops opened for service on February 19, 1962, enabling the doors of all eight cars of trains to open on the platform. Work was still underway at two of the other three stations part of the contract, Wall Street and Fulton Street, while work at Bowling Green was already completed.^[39] The entire platform-lengthening project was substantially completed by November 1965.^[40]

Because the Lexington Avenue Line during the 1970s was known to frequent muggers due to the dilapidated state of the subway at the time, the Guardian Angels, founded by Curtis Sliwa, began operations on February 13, 1979, by conducting unarmed night patrols on the 4 train in an effort to discourage crime.^[41] These patrols later expanded to other parts of the subway and to other city neighborhoods.^[42]

On August 28, 1991, an accident involving a 4 train on the express track just north of the 14th Street–Union Square station killed five riders and injured 215 others in the worst accident on the system since the 1928 Times Square derailment.^[43][44] As a result of the crash, new safety protocols were put in place and there was a partial implementation of automation of the New York City Subway.^[45]