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. 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; in turn, the Second and Third Avenue elevated lines were to be knocked down to make room for the 6-track subway. The paper was revised in January 1927.