The 9 designation was originally used for the IRT Dyre Avenue Line

IRT Dyre Avenue Line

The IRT Dyre Avenue Line is a New York City Subway rapid transit line as part of the A Division . It is a branch of the IRT White Plains Road Line serving passengers in the northeastern section of the Bronx...

 upon its opening in 1941 between Dyre Avenue and the East 180th Street platforms of the former New York, Westchester and Boston Railway

New York, Westchester and Boston Railway

The New York, Westchester and Boston Railway Company , known to its riders as "the Westchester" and colloquially as the "Boston-Westchester", operated as an electric commuter railroad in the Bronx and Westchester County, New York from 1912 to 1937...

, connecting to the IRT White Plains Road Line

IRT White Plains Road Line

The White Plains Road Line is a rapid transit line of the IRT division of the New York City Subway, serving the central Bronx. It is mostly elevated, and served both subway and elevated trains until 1952...

 at the latter station. When a connection between the Dyre Avenue Line and the White Plains Road Line opened in 1957, daytime shuttle service was replaced with through service as the . From 1957–1966, the nighttime Dyre Avenue Shuttle continued to use the number 9. Since 1967, the Dyre Avenue Shuttle runs during late night hours, but now carries the number , the same as the through service on the line.

Broadway – Seventh Avenue Line skip-stop service (1989–2005)

The second and most recent usage of the 9 designation was a skip-stop

Skip-stop

Skip-stop is a public transit service pattern which reduces travel times and increases capacity by not having all vehicles make all designated stops along a route. Skip-stops are used in both rail transit and bus transit operations.-Rail operation:...

 service to complement the local train on the IRT Broadway – Seventh Avenue Line as the 9 Broadway – Seventh Avenue Line Local. Beginning at 6:30 AM on Monday, August 21, 1989, the services were coordinated as the /9 and both ran between Van Cortlandt Park – 242nd Street and South Ferry. The skip-stop operation was north of 137th Street.

Midday skip-stop service was discontinued in 1994, but remained during peak hours. By this time, skip-stop service assigned the following stations to the train only:

• 238th Street
• 215th Street
• Dyckman Street
• 157th Street

and the following stations to the 9 train only:

• Marble Hill – 225th Street
• 207th Street
• 145th Street

After the September 11, 2001 attacks

September 11, 2001 attacks

The September 11 attacks The September 11 attacks The September 11 attacks (also referred to as September 11, September 11th or 9/119/11 is pronounced "nine eleven". The slash is not part of the pronunciation...

, trains had to be rerouted since the IRT Broadway – Seventh Avenue Line ran directly under the World Trade Center site

World Trade Center site

The World Trade Center site , also known as "Ground Zero" after the September 11 attacks, sits on in Lower Manhattan in New York City...

 and was heavily damaged in the collapse of the South Tower. The service ran only between Van Cortlandt Park – 242nd Street and 14th Street, running local north of 96th Street and express south of there; the 9 service and skip-stop service were suspended at this time.

Service was changed again, on September 19 after a few switching delays at 96th Street. trains made all local stops from 242nd Street to New Lots Avenue via the Clark Street Tunnel

Clark Street Tunnel

The Clark Street Tunnel carries the trains of the New York City Subway 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...

 and IRT Eastern Parkway Line

IRT Eastern Parkway Line

IRT Eastern Parkway Line and New Lots Line can refer to:* IRT Eastern Parkway Line* IRT New Lots Line...

, to replace trains, which terminated at 14th Street. trains returned to South Ferry, and skip-stop service was restored on September 15, 2002.

The 9 service and skip-stop service were discontinued completely at 5 AM on Tuesday, May 31, 2005, including the peak-hour service that had run since 1994. The last day of 9 service was on Friday, May 27, 2005.