In December 1934, at the insistence of the Automobile Club of New York, several numbered routes were extended and signed within New York City, with NY 100 being one of these routes. NY 100 was extended south from the Yonkers line in the Bronx along Jerome Avenue to the Grand Concourse. NY 100 crossed into Manhattan via East 149th Street and the 145th Street Bridge. In Manhattan, NY 100 continued south along Lenox Avenue, 110th Street, Fifth Avenue, 96th Street, and Park Avenue, ending at Houston Street (NY 1A). South of Fordham Road, NY 100 was overlapped with NY 22 all the way to Houston Street. The NY 100 designation was removed from New York City following the opening of the Major Deegan Expressway in 1956.