Its route emblem, or "bullet", is colored red, since it uses the Interborough Rapid Transit Company's (IRT) Broadway–Seventh Avenue Line.

[4] The 1 operates 24 hours a day between Van Cortlandt Park–242nd Street in Riverdale, Bronx and South Ferry in Lower Manhattan, making all stops along the full route.

The modern 1 train has always run up to Van Cortlandt Park in the Bronx, but its route below 96th Street has varied through the years.

When the New York City Subway began operation between 1904 and 1908, one of the main service patterns was the West Side Branch, which the modern 1 train uses.

[5][6][7] On November 15, 1906, a petition with 20,000 signatures was sent to the Rapid Transit Commission to request the restoration of express service on the third track north of 96th Street.

[9] Limited express service was inaugurated on November 19, 1906, operating daily, except Sundays and holidays, between 7:20 and 8:58 a.m. and 4:54 and 6:18 p.m. to and from 181st Street.

[12] In December 1906, the IRT prepared plans to relieve overcrowding on the platforms at 96th Street and train congestion at the station.

To reduce the significant number of people transferring between people taking Lenox Avenue Line locals and Broadway express trains, the IRT planned to have Broadway express trains pass through the station without stopping.

[18] Finally, the new "H" system was implemented on August 1, 1918, joining the two halves of the Broadway–Seventh Avenue Line and sending all West Side trains south from Times Square.

[24] Beginning on May 10, 1946, all 1 trains in Brooklyn ran express during late nights, with service running every twelve minutes.

Trains then stopped using the switches north of 96th Street, except for General Orders, when temporary construction-related service diversions were in effect.

Trains began to be branded as Hi-Speed Locals, being as fast as the old express service with new R21 and R22 subway cars on the route.

However, the agency settled on skip-stop service because the center track existed in two discontinuous segments, which would require complicated track-switching maneuvers to accommodate the express trains.

[43] Skip-stop trains would not speed through stations, instead passing through skipped stops at 15 mph (24 km/h); the maximum allowed per NYCTA rules.

Skip-stop service was expected to speed up travel times for almost half of riders north of 96th Street.

[46] In September 1988, the MTA Board formally voted to defer implementation of 1/9 skip-stop service for these reasons.

However, residents of Inwood and Washington Heights were particularly opposed to the change, since most stops in these neighborhoods would be skipped by one of the two routes, and since they had not been included in the planning process.

[48] In March 1989, the NYCTA stated that there was no set date for the implementation of the plan, with service possibly starting as late as the fall.

To convince local communities, it set up meetings with residents and distributed leaflets advertising the change.

One change was made from the 1988 plan: due to community input 181st Street was added as an all-stop station.

[51] Beginning at 6:30 a.m. on Monday, August 21, 1989, the services were coordinated as the 1/9 and both ran between Van Cortlandt Park–242nd Street and South Ferry.

[58][59] After the September 11 attacks in 2001, 1 trains had to be rerouted since the IRT Broadway–Seventh Avenue Line ran directly under the World Trade Center site and was heavily damaged in the collapse of the Twin Towers.

It initially ran as a shuttle alongside the 2 and 3 trains to Times Square, due to debris that fell on the tracks south of Pennsylvania Station.

However, the Cortlandt Street station, which was directly underneath the World Trade Center, was demolished as part of the clean-up and was rebuilt as part of the World Trade Center Transportation Hub until September 8, 2018, when it reopened as WTC Cortlandt.

[68] Though the MTA had planned to vote on the future of the skip-stop service in summer 2004,[67] it approved the change on January 11, 2005.

Rector Street served as a temporary terminal for the 1 until April 4, 2013,[72][73] when the 1 returned to the reopened loop station.