The United States has approximately 72 mi (116 km) of road tunnels. About 29 mi (47 km) of these tunnels are along the Interstate highway system. The tunnels along the U.S. Interstate highway system have been constructed over many years utilizing a variety of construction methods, equipment, and contract mechanisms. Construction methods varied primarily according to the subsurface geologic conditions encountered, current tunneling methods, and economic considerations. The majority of tunnels were constructed using the design-bid-build contracting methods. However, some were constructing using design-build methods especially in the recent past. These tunnels were required to go under a number of natural obstacles, most often rivers and mountains. Occasionally, depressing highways underground in congested urban areas have presented additional opportunities for surface reclamation or air rights developments. The shortest Interstate highway tunnel is the Reverse Curve Tunnel on Interstate 70 (I-70) approximately 600 ft (183 m) long. The longest Interstate highway tunnel is the Brooklyn Battery Tunnel on I-478 approximately 1.7 mi (2.8 km) long. The Brooklyn Battery Tunnel is also the longest subaqueous tunnel on the Interstate highway system. The highest highway Interstate tunnel in the United States is the Eisenhower Tunnel on I-70 at a maximum elevation of 11,152 ft (3,401 m). This paper identifies several tunnels that have been constructed along the Interstate highway system over the past 50 years. Specific examples of the various tunneling methods and contracting practices used are highlighted.
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