Originally a streetcar line, it is now the M14 bus route, operated by the New York City Transit Authority.

[3] The M14A/D SBS routes supplement the 14th Street Line (L train), which runs from Eighth Avenue and continues into Brooklyn.

Buses were substituted for streetcars by the New York City Omnibus Corporation on April 20, 1936.

[7] In 1956, New York City Omnibus Corporation became Fifth Avenue Coach Lines; the Manhattan and Bronx Surface Transit Operating Authority (MaBSTOA) subsidiary of the New York City Transit Authority took over operations in 1962.

This new route began running late and caused confusion with the M21 on Avenue C and eventually service returned to its current state as the M14A and M14D.

[12] The Select Bus Service route was to be implemented by January 6, 2019, three months before the tunnel was set to shut down.

[14][15] After the 14th Street Tunnel work was completed, some version of M14 SBS service would continue operating.

[16] On January 4, 2019, Governor Andrew Cuomo announced that the L train shutdown would be modified.

[26][27] However, due to a lawsuit, the busway was not implemented as scheduled,[28][29] and after another delay that August,[30][31] went into effect on October 3, 2019.

[32][33] The busway was so successful on its first day that M14 buses had to be slowed down in order to keep from running ahead of their posted schedules.

[34] In December 2019, the M14A/D SBS were the launch routes for the MTA's new battery-electric New Flyer Xcelsior XE60 buses.