The origin of tunnel building is disputed. The Egyptians built tunnels as entrances to tombs. The Babylonians built (c.2180 B.C.) a tunnel under the Euphrates using what is now called the "cut-and-cover" method; the river was diverted, a wide trench was dug across its bed, and a brick tube was constructed in it and covered up. The ancient Greeks and Romans built tunnels for carrying water and for mining purposes; some of the Roman tunnels are still in use. One of the first notable tunnels in Great Britain was part of the Grand Trunk Canal. It was nearly 2 mi (3.2 km) long and was completed in 1777. The Mont Cénis Tunnel, a railroad tunnel in the French Alps that opened in 1871 and is now 8.5 mi (13.7 km) long, was probably the first tunnel built using compressed-air drills.
The first tunnel of importance in the United States was the tunnel through the Hoosac Range in Massachusetts. There are hundreds of miles of tunnels in New York City and its vicinity, e.g., for subways, roads, water systems, and railroads. The Delaware Aqueduct, which provides part of New York City's water supply, is at 105 mi (168 km) the longest continuous tunnel in the world. Road tunnels include the Holland Tunnel and the Lincoln Tunnel, which connect New York City's Manhattan Island with New Jersey, and the Hugh L. Carey (formerly Brooklyn-Battery) Tunnel, which connects Manhattan Island with Brooklyn and is the longest vehicular tunnel (1.7 mi/2.7 km) in the United States. The Anton Anderson Memorial Tunnel, also known as the Whittier Tunnel (2.5 mi/4 km), which opened in 1943 to rail traffic and in 2000 to vehicular traffic, connects Whittier, Alaska, to Anchorage and other cities; the unique single-lane tunnel allows rail or road traffic in one direction only at a time. The Chesapeake Bay Bridge-Tunnel in Virginia, opened in 1964, has a length of 17.6 mi (28.2 km) and includes two tunnel segments over a mile long.
The Simplon Tunnel (see under Simplon) through the Alps, for many years the longest railway tunnel in the world, consists of two parallel single-line tunnels (both 12.3 mi/19.8 km) with connecting tunnels at short intervals. The Channel Tunnel (Chunnel) under the English Channel is much longer, at 31 mi (50 km), and the Seikan Tunnel in Japan, the world's deepest underwater tunnel, is also the longest railroad tunnel at 33.5 mi (53.6 km). The Gotthard Base rail tunnel, expected to open in 2016, is 35 mi (57 km) in length; the main boring was completed in 2010. The world's longest vehicular tunnel, the Lærdal Tunnel (15.2 mi/24.5 km long), connects Lærdal and Aurland, Norway, and is an important overland link between Oslo and Bergen. The St. Gotthard Tunnel (10.2 mi/16.4 km long), in the Swiss Alps, was formerly the longest vehicular tunnel.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.