 In 1944 , Mayor Fiorello H. La Guardia announced that work on the Second Avenue subway line was progressing . The same year , BOT superintendent Philip E. Pheifer came up with a map of train frequencies for the line , with about 56 trains per hour projected to go through the Second Avenue line . Pheifer also put forth a proposal for Second Avenue Subway services , which would branch extensively off to B Division lines , including the IND Sixth Avenue Line , BMT Broadway Line , and BMT Nassau Street Line , via pre @-@ existing BMT trackage over the Manhattan and Williamsburg Bridges . From Canal Street to 57th Street the line was to be four tracks , with six tracks north of 57th Street . South of Canal Street there would be two tracks . The subway was to be opened by 1951 . In addition , a new Bronx Branch would replace the Third Avenue El in the Bronx . By 1945 , though , plans for the Second Avenue Subway were again revised . The southern two @-@ track portion was abandoned as a possible future plan for connecting the line to Brooklyn , through a Bronx route to Throggs Neck was put forth . 
