Cumberland Gap Tunnel
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The Cumberland Gap Tunnel is a tunnel that carries U.S. Highway 25E under Cumberland Gap National Historical Park near the intersection of Kentucky, Tennessee, and Virginia. The east portal of the tunnel is in Tennessee and the west portal is in Kentucky; according to United States Geological Survey maps of the area, the tunnel does not enter Virginia. It is one of only two mountain vehicular tunnels in the United States that crosses a state line, the other being the East River Mountain Tunnel on Interstate 77 between Virginia and West Virginia.
[edit] Data
The tunnels consist of two tubes, each 4,600 feet (1,402 m) long. Each tube carries two lanes of traffic. An "illumination zone" is included at each portal to allow drivers' vision to adjust to the lower light level in the tunnel. The speed limit in the tunnel is 45 mph (70 km/h); lane changes are prohibited. Trucks carrying hazardous cargo are prohibited from using the tunnels. The overall construction cost, including the four-lane approach roads at both portals, was USD 280 million.
The tunnel replaced a 2.3-mile (3.7 km) stretch of U.S. 25E between Middlesboro, Kentucky and Cumberland Gap, Tennessee that became known as "Massacre Mountain" due to the large number of travelers killed on the twisting mountain road over the Cumberland Gap pass.
[edit] Project history
Even in the late 1970s, road traffic through the park had increased to the point of being unmanageable, and the project to replace the surface road began in 1980. However, construction did not begin until 1991. Early on, it was decided that widening the existing surface road to four lanes would adversely affect the historically sensitive areas in the park, making a tunnel the only viable choice. As a part of the plan, the existing road through Cumberland Gap has been removed and restored as a wagon path similar to that used by early nineteenth century travelers.
Construction was administered by the Eastern Federal Lands Highway Division of the Federal Highway Administration for the National Park Service, with funding provided by both agencies as well as the states of Kentucky and Tennessee. While the project was in the planning phases, Kentucky and Tennessee both began widening their portions of US 25E leading to Cumberland Gap to four lanes.
The first step in construction was the boring of a pilot tunnel underneath the mountain, which revealed some unexpected construction challenges. The boring revealed underground springs and streams that would result in leakage of 450 gallons (1,700 L) per minute of water into the tunnel, regardless of outside weather conditions. To eliminate leakage into the tunnel, the tubes were lined with a thick PVC layer.
Construction of the actual tubes began on June 21, 1991. Excavation continued simultaneously from both sides, and the tunnels were joined on July 9, 1992. The tunnels opened to traffic on October 18, 1996.
