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 saw an average of 1.3 million daily riders in 2015; this is more than the daily ridership of the second-busiest subway system in the U.S., the Washington Metro, as well as more than the combined daily riderships of San Francisco's and Boston's transit systems. Local bus routes are just as crowded during various times of the day, with the parallel M15 local and M15 Select Bus Service routes seeing 46,000 passengers per weekday in 2016, translating to 14.5 million passengers that year.