 With the city 's economic and budgetary recovery in the 1990s , there was a revival of efforts to complete construction of the SAS . Rising ridership on the IRT Lexington Avenue Line , the only subway trunk line east of Central Park , demonstrated the need for the Second Avenue Line , as capacity and safety concerns rose . The four @-@ track IRT Lexington Avenue Line , the lone rapid transit option in the Upper East Side and East Harlem since the 1955 closure of the Third Avenue elevated , is the most crowded subway line in the country . The line sees an average of 1 @.@ 3 million daily riders , more than the entire Washington Metro system ( which has the second @-@ highest ridership in the U.S. ) and more than the rail transit systems of San Francisco and Boston combined . Local bus routes are just as crowded during various times of the day , with the surface Second Avenue Line , carrying the M15 and M15 SBS buses , seeing an annual ridership of 17 @.@ 5 million , or a daily ridership of about 47 @,@ 945 . The construction of the Second Avenue line would add another two tracks to fill the gap that has existed since the elevated Second and Third Avenue Lines were demolished in the 1950s . 
