Rocky Start

From the outset, there were no easy decisions about where and how the bridge would take shape. In July 1998, CH2M Hill Inc., Englewood, Colo., prepared an environmental impact statement that drew 160 public and agency comments, due to the historic nature of the dam and the neighboring Lake Mead Recreation area. Options included a $204-million, 2,200-ft-long bridge and 3.5-mile roadway about 1,000 ft upstream of the dam, a $215-million, 1,700-ft-long bridge and 3.3-mile roadway at Gold Strike Canyon one mile downstream, or a no-build alternative. FHWA selected the current alignment at Sugarloaf Mountain, roughly 1,600 ft downstream of the dam.

�The Gold Strike Canyon alignment was favored by a lot of the stakeholders because it wasn�t visible from the dam,� says Bill Dowd, executive vice president with HDR Inc., Omaha, which performed bridge studies for the EIS. �It didn�t detract from the aesthetics, but it had more environmentally sensitive surrounding park area. The Sugarloaf alignment was already pretty well disturbed and made the most sense based on its engineering and operational advantages.� In 2001, FHWA awarded a six-year, $22-million design and engineering assistance contract to HDR, with Jacobs Engineering Group Inc., Pasadena, Calif., and San Francisco-based T.Y. Lin International.

But the Sugarloaf Mountain alignment presented its own difficulties. A 12-month geotechnical survey by London-based AMEC plc found Black Canyon�s slopes would require costly excavation to place the bridge�s foundation. Contractors would have to create 90� and 73� sheer drops at the Nevada and Arizona sides, respectively, to minimize the amount of excavation otherwise needed for more gradual roadway transitions. That raised the price tag by 15.4%, to $234 million from $198 million. The project also has a $6-million contingency fund for a $240-million total cost.

Controlled explosives were used to carve out the canyon walls, which descend 850 ft to the Colorado River. Crews placed some 80 rock bolts to stabilize vertical angles, and the subsurface to withstand the bridge�s dynamic forces.

As rugged as the site of the crossing is, the approaches were no easier. The new 4.3-mile highway alignment snakes through harsh terrain in the Lake Mead National Recreation Area, with abrupt drops, jutting rock surfaces and uneven contours. The dam�s historic nature and visitor areas, as well as federally protected plant and wildlife, played a key role in determining the roadway route.

�The topography for the bypass is an extremely harsh and challenging terrain, with dips, ravines and traverses,� says FHWA project manager F. Dave Zanetell. �The route was laid down to minimize environmental impact as much as possible by passing over areas that had been previously disturbed.�

The new four-lane asphalt highway follows a winding route in Nevada just south of existing U.S. 93. It crosses over the existing roadway twice before crossing the Colorado River past Sugarloaf Mountain, then tying into U.S. 93 in Arizona.