The Upper East Side is a neighborhood in the borough of Manhattan in New York City, between Central Park and the East River. The Upper East Side is within an area bounded by 59th Street, 96th Street, Central Park, and the East River. Once known as the 'Silk Stocking District', it has some of the most expensive real estate in the United States. The Upper East Side is currently served by one subway line, the four-track IRT Lexington Avenue Line (4 5 6 <6>), and local bus routes. Due to severe congestion on the subway and buses, the Metropolitan Transportation Authority is currently building a new subway line, the Second Avenue Subway, along Second Avenue. The first phase will run from 96th Street to 63rd Street, where it will physically connect with the BMT Broadway Line; service will be provided by a northern extension of the Q train. In later phases, the line will be extended north to 125th Street/Park Avenue in Harlem and south to Hanover Square in the Financial District, and a new T service will run its entire length