The first regularly operated line of the New York City Subway was opened on October 27, 1904, and was operated by the Interborough Rapid Transit Company (IRT). The early IRT system consisted of a single trunk line running south from 96th Street in Manhattan (running under Broadway, 42nd Street, Park Avenue, and Lafayette Street), with a southern branch to Brooklyn. North of 96th Street, the line had three northern branches in Upper Manhattan and the Bronx. The system had four tracks between Brooklyn Bridge–City Hall and 96th Street, allowing for local and express service. The original line and early extensions consisted of:
- The IRT Eastern Parkway Line from Atlantic Avenue–Barclays Center to Borough Hall
- The IRT Lexington Avenue Line from Borough Hall to Grand Central–42nd Street
- The IRT 42nd Street Shuttle from Grand Central–42nd Street to Times Square
- The IRT Broadway–Seventh Avenue Line from Times Square to Van Cortlandt Park–242nd Street
- The IRT Lenox Avenue Line from 96th Street to 145th Street
- The IRT White Plains Road Line from 142nd Street Junction to 180th Street–Bronx Park
Planning for a rapid transit line in New York City started in 1894 with the enactment of the Rapid Transit Act. The plans were drawn up by a team of engineers led by William Barclay Parsons, chief engineer of the Rapid Transit Commission. The city government started construction on the first IRT subway in 1900, leasing it to the IRT for operation under Contracts 1 and 2. After the initial line was opened, several modifications and extensions were made in the 1900s and 1910s.