The runway layout has changed little, except for the 1956 closure of a fourth, east–west runway now used for taxiing and aircraft parking. The terminal building was supplemented by the North Terminal in 1958; the two were connected in 1961. A United Airlines holdroom complex was built in 1965, and a facility for American Airlines was completed in 1968. A commuter terminal was constructed in 1970.[1] In March 2012 the main 1/19 runway was lengthened 300 ft to add FAA compliant runway safety areas.[16]
Despite the expansions, efforts have been made to restrict the growth of the airport. The advent of jet aircraft as well as traffic growth led Congress to pass the Washington Airport Act of 1950, which resulted in the opening of Dulles Airport in 1962. Concerns about aviation noise led to noise restrictions even before jet service began in 1966. To reduce congestion and drive traffic to alternative airports, the FAA imposed landing slot and perimeter restrictions on National and four other high-density airports in 1969.[17]