[5] The elevated trains were noisy and often dirty (in the 19th century they were pulled by soot-spewing steam locomotives).

The line was finally torn down in 1942 because it was deteriorated and obsolete, and the cost of World War II made upkeep impossible.

[6] Second Avenue maintains its modest architectural character today, despite running through a number of high-income areas.

[7] A protected bike lane on the left, or east, side of the avenue between 59th and 68th streets was completed in 2019.

[17] Eleven other buildings were evacuated as a result of the explosion, and Con Ed turned off the gas to the area.

[20] Two short sections of the line have been completed over the years, serving other subway services (the Grand Street station is served by the B and ​D trains), and others simply sitting vacant underground (such as the unused upper level at the Second Avenue station on the F and ​ trains).

[22] Construction on Phase 1, which will eventually extend from 125th Street to the Financial District via the T service, began on April 12, 2007.

[23] Phase 2, which would extend the line to East Harlem at 125th Street and Lexington Avenue, is expected to be completed between 2027 and 2029.