New Utrecht Avenue and started operating on March 16, 1915. Additional cars were equipped with poles and operated service on the line from May 1, 1915, until the line opened for full subway service on June 22, 1915, with trains running between Coney Island and Chambers Street in Lower Manhattan. Service started with two- and three-car trains operating via the Fourth Avenue local track and the Manhattan Bridge south tracks. The express tracks were finished several weeks later. When the BMT Fourth Avenue Line was extended south from the Sea Beach Line on January 15, 1916, the Sea Beach trains were shifted to the express tracks on Fourth Avenue, with Fourth Avenue trains providing local service. The tracks over the north side of the Manhattan Bridge opened on September 4, 1917, along with part of the BMT Broadway Line. All Sea Beach service was moved to the new line, ending at 14th Street–Union Square. This was extended to Times Square–42nd Street on January 5, 1918. In 1924, the BMT assigned numbers to its services. The Sea Beach Line service became the 4. This has since become the train. In general, Sea Beach service has always run express in Manhattan and on Fourth Avenue in Brooklyn, ending at 42nd Street and later 57th Street. The began on November 27, 1967, as a "super-express" from Brighton Beach on the BMT Brighton Line through Coney Island–Stillwell Avenue, and along the Sea Beach Line express tracks to 57th Street with only seven stops between Stillwell Avenue and 57th Street, three in Brooklyn and four in Manhattan. This service was discontinued on April 15, 1968, due to low ridership, and no regular trains have used the Sea Beach express tracks since. Later years In the 1970s, there was a proposal to renovate the Sea Beach open cut, which was deteriorating to the point that a retaining wall along the line was in danger of collapsing onto the tracks. Funding was allocated for the line's infrastructure improvements in 1975. More than $20 million was earmarked for New York City Subway projects in 1977, including for upgrades to the Sea Beach line. When Coney Island–Stillwell Avenue was closed for reconstruction from 1993 to 1995 and November 4, 2001, to May 29, 2005, 86th Street was the southern terminal for the N train.Typical station pre-renovationTypical station post-renovation In October 2013, it was announced that the line would under