This station was part of the original subway, and has two side platforms and three tracks, the center one being an unused express track.
The southbound local track is known as BB1 and the northbound one is BB4; the BB designation is used for chaining purposes along the Broadway–Seventh Avenue Line from 96th Street to 242nd Street and not in everyday speech.
Although it cannot be accessed at 103rd Street, the center track is designated as M.
There is a mezzanine above the platforms, which contains the fare control area, as well as stairs to the street and both platforms.

This is the southernmost 3-track station on the line.
South of the station, there are switches that connect the express track to either local track, with trains then being able to crossover to the rising express tracks from the IRT Lenox Avenue Line.
Under 103rd Street, the dual express tracks serving the southern part of the line descend and curve to the east to form the IRT Lenox Avenue Line.
They turn off of Broadway and onto 104th Street directly underneath this station.
An emergency exit from the Lenox Avenue Line is located in the middle of the northbound platform.
This station was part of the original subway, and has two side platforms and three tracks, the center one being an unused express track. The southbound local track is known as BB1 and the northbound one is BB4; the BB designation is used for chaining purposes along the Broadway–Seventh Avenue Line from 96th Street to 242nd Street and not in everyday speech. Although it cannot be accessed at 103rd Street, the center track is designated as M.
There is a mezzanine above the platforms, which contains the fare control area, as well as stairs to the street and both platforms.
This is the southernmost 3-track station on the line. South of the station, there are switches that connect the express track to either local track, with trains then being able to crossover to the rising express tracks from the IRT Lenox Avenue Line. Under 103rd Street, the dual express tracks serving the southern part of the line descend and curve to the east to form the IRT Lenox Avenue Line. They turn off of Broadway and onto 104th Street directly underneath this station. An emergency exit from the Lenox Avenue Line is located in the middle of the northbound platform.
103rd Street station (IRT Broadway–Seventh Avenue Line)