Hoover Dam needs more concrete

News August 27, 2001
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It's a long way down the Hoover Dam

It's a long way down the Hoover Dam. It's a long way across it, too.

Traffic congestion along U.S. Highway 93, a two-lane road which carries approximately 11,500 vehicles daily past the historic landmark, has cars backing up like the water these days. According to reports, within five years for three hours of every day there will be a delay of 30 minutes or greater just to get through the dam itself under the current system. In 25 years, the number would increase to 10 hours of every day.

Transportation planners, however, have a plan to cut the steel loose. Designs for an alternate route used by local commuters are in place.

"The existing facility was identified by the state of Nevada as being inadequate to handle the traffic as early as 1965," Dave Zanetell, project manager for the Central Federal Lands Highway Division, Denver, told ROADS&BRIDGES. "You have a roadway alignment that has about a 15 mile-per-hour design speed through that area."

The twists and curves can throw motorists on two wheels if they're not careful. Trucks comprise 20% of the average daily traffic and have to stop at various points to allow oncoming rigs to swing around turns.

"It's just so narrow and so restrictive on the horizontal and vertical alignment," said Zanetell. "In terms of accident history, it's three times greater than similar volume roads in the state of Arizona and the state of Nevada."

Final designs came down to the best of three. The Sugarloaf Mountain Alternative, located about 1,500 ft downstream of Hoover Dam, was the winner. The $198 million, four-lane option contains either a steel deck arch or cable-stayed bridge and will take five years to construct. It is approximately 3.2 miles long, with the total length of the bridge listed at about 1,900 ft.

Gold Strike and Promontory Point were the other choices. The Gold Strike Alternative would cross the Colorado River about one mile downstream and offered the choice of a concrete deck arch or steel deck arch bridge. The price tag was $215 million and the project timetable was set at 5-6 years. Although the option created the least disturbance to traffic during construction, the roadway geometrics were poor. Promontory Point featured a steel suspension, cable-stayed or steel truss rib-through arch span and was marked at $204 million. The job, however, had the most complex bridge design and construction.

"(The Sugarloaf Mountain Alternative) essentially has the best operational dynamics," said Zanetell. "It has the easiest approaches to the bridge construction. It is marginally cheaper in estimated cost and it has by far and away the least environmental impact. It was also favored by the public by a ratio of 3 to 1.

"We have two potential bridge types, and now we will evaluate all potential bridge types to make sure we look at all the most feasible, cost effective and practical bridges in addition to evaluating their compatibility with the Hoover Dam, which is a major consideration."

The Hoover Support Team, consisting of HDR Inc., Sverdrup Civil and T.Y. Lin International, is currently conducting mapping, geotechnical and alignment studies on the new highway. The first contract, for approach construction in Arizona, will be awarded in late 2002.

"The transportation needs for this facility are overwhelming," said Zanetell. "It's an exciting project."


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