 After World War I , the New York City Subway experienced a surge in ridership . By 1920 , 1 @.@ 3 billion annual passengers were riding the subway , compared to 523 million annual riders just seven years before the war . In 1919 , the New York Public Service Commission launched a study at the behest of engineer Daniel L. Turner to determine what improvements were needed in the city 's public transport system . Turner 's final paper , titled Proposed Comprehensive Rapid Transit System , was a massive plan calling for new routes under almost every north @-@ south Manhattan avenue , extensions to lines in Brooklyn and Queens , and several crossings of the Narrows to Staten Island . Massively scaled @-@ down versions of some of Turner 's plans were found in proposals for the new city @-@ owned Independent Subway System ( IND ) . Among the plans was a massive trunk line under Second Avenue consisting of at least six tracks and numerous branches throughout Brooklyn , Queens , and the Bronx . Turner also proposed that the two elevated lines be knocked down to make room for the 6 @-@ track Second Avenue Subway . The plan was to connect the new line to the then @-@ unbuilt Sixth Avenue and Eighth Avenue subway lines . 
