Wikipedia: First Avenue is a north-south thoroughfare on the East Side of the New York City borough of Manhattan, running from Houston Street northbound for over 125 blocks before terminating at the Willis Avenue Bridge into The Bronx at the Harlem River near East 127th Street. South of Houston Street, the roadway continues as Allen Street south to Canal Street. Traffic on First Avenue runs northbound (uptown) only. First Avenue passes through a variety of mostly residential neighborhoods. Between 42nd Street and 45th Street, it borders the United Nations headquarters complex, and four lanes are underground. Like all of Manhattan's major north-south Avenues, First Avenue was proposed as part of the Commissioners' Plan of 1811 for Manhattan, which designated 12 broad north-south Avenues running the length of the island. The southern portions of the Avenue were cut and laid out shortly after the plan was adopted. The northern sections of the Avenue would be graded and cut through at various intervals throughout the 19th Century as the northward development of the island demanded. The IRT Second Avenue Line ran above First Avenue from Houston Street to 23rd Street before turning left at 23rd and then right onto Second Avenue. The El was torn down in 1942.