The Hanging Lake Viaduct under construction, with old U.S. Highway 6 still carrying traffic on the lower roadway.Images courtesy Figg Engineering Group.

Hanging Lake Viaduct: A Case Study

Bridges are among the largest and most imposing of engineered structures. In the past great bridges were built to call attention to themselves and to the engineers' ability to overcome great obstacles. As a result, they often reshaped their environments: Who can now think of the magnificent natural opening of San Francisco Bay, dubbed "the Golden Gate" by early explorers, without thinking of the great bridge set across it in the 1930s?

Sometimes, however, it seems best that a structure not so much reshape our perceptions of a space as enhance them. In Colorado's Glenwood Canyon a key link in the nation's interstate highway system required the construction of a viaduct to carry the road over a narrow, curving, and very beautiful stretch of the Colorado River. The Hanging Lake Viaduct was built with special attention to fitting into this precious natural setting, while providing an efficient and reliable transportation link.

Meeting the challenge in Glenwood Canyon involved not only designing a structure that would harmonize with its environment but also minimizing harm to the river and its surroundings. The builders used a giant gantry and crane to set the precast concrete box girders of the bridge into place from above. The number of piers supporting the road was reduced by making spans as long as 300 feet. Bridge members were designed with straight lines to blend with the striations of the canyon walls.

Plans show the placement of temporary support columns that carried the viaduct above U.S. 6 during construction.