LAST LINKS FOR WASHINGTON METRO RAIL

Engineers of the Washington Metropolitan Area Transit Authority (WMATA) have almost completed the Metro in the USA's capital city. Construction of its 103.6-mile network began in 1975, and contractors are now excavating the final underground section. The last line is due to open in 2001. The Metro will have 50.7 miles of tunnels and 47 underground stations. The major construction now in progress will complete the Mid-City E Route, a central link of the Green Line, and the Outer F Route, the line's extension south east into Maryland. The E Route tunnels will include open-face shield-driven tunnels with 9in-thick, lightly reinforced, precast segmental primary support and cast-in-place concrete final lining with 16in average thickness. This tunnelling method was chosen to maximise tunnel advance rate, while installing a waterproofing system to prevent ground water ingress. On the Outer F Route, construction methods include the New Austrian Tunnelling Method (NATM), use of an earth-pressure balance tunnel boring machine with concrete segment lining, and cut+cover. Subject to the availability of funding, there are proposals for several further extensions to the Washington Metro.