Bridges & Tunnels

Bridges and tunnels have been essential to infrastructure growth in highways, railroads, roads, shipping and maritime transport and travel. The simplest bridge form is the beam or girder bridge, constructed from rigid beams of steel or concrete placed across a span. The earliest bridges, dating before the Roman arch bridge, were made of wood and stone beams. Reinforced concrete bridge construction, in which steel imbedded in the concrete, controls the force of tension, was introduced in the United States in the late nineteenth century.

One major type of bridge construction is the suspension bridge, for instance the Golden Gate bridge in San Francisco completed in 1937. A number of large suspension bridges were built during the first half of the twentieth century, such as the Manhattan Bridge in 1909 and the massive George Washington Bridge competed 1931. One of the few suspension bridges built in the United States after the middle of the twentieth century is the Verrazano-Narrows Bridge which opened in November 1964. This bridge is situated across the entrance to the New York Harbor and connects Brooklyn and Staten Island. With the expansion of American railroads nearing its end, the interstate highways and road travel became a major factor in bridge and tunnel design. Tunnel design and construction for transportation often comprises two or three large, parallel passages for opposite direction car and vehicle traffic. One of the most anticipated tunnels for transporting people by rail or cars is the Channel Tunnel, 23 miles of which are underwater and competed in 1994, connects Great Britain to the European continent.