Hoover Dam bypass bridge rises under a shadow

The Hoover Dam bypass bridge looks spectacular, stretching 1,900 feet across Black Canyon and 900 feet above the churning Colorado River. Tourists visiting the world-famous Hoover Dam can’t help but swing around and snap photos of the new span high above.

Long before its completion, it was labeled a "civil engineering marvel."

Perhaps the toughest challenges associated with building the long-awaited bridge linking Arizona and Nevada had less to do with technology and the daunting dimensions and more to do with respecting the true engineering marvel 1,500 feet upstream. At least that is the opinion of one well-respected civil engineer.

"I think the challenge was to make it come up to the iconic standards of the Hoover Dam, building something in such close proximity to a world-class structure like that," said Henry Petroski, a civil engineering professor at Duke University. "The engineers involved were very conscious of this, that they were working with a site that had to be respected."

Although the staggering size and prominence of the span finds itself the centerpiece of photographs, it is still the 75-year-old Hoover Dam that lures tourists away from the glitz and glamour of the Strip.

The $240 million bridge has taken nine years to materialize from the drawing board. When it opens to traffic, now scheduled for next week , it will be a relief to commuters, to interstate travelers and, especially, to the truckers who for nine years have taken the long way through Laughlin to deliver their goods to Las Vegas. The opening also is highly anticipated by locals and tourists, who are anxious to catch a view of Hoover Dam only previously available by helicopter.

While the bridge is majestic in its own right, it hasn’t stolen the spotlight from its famous neighbor.

"Bridges similar to that were built before," said Bill Bahrenburg, a Long Island, N.Y., resident who recently toured the dam with his wife, Coretta. "But the dam was built in the 1930s, before they had all that equipment."

The equipment used to build the largest concrete arch bridge in the Western Hemisphere obviously is far more advanced than what was available to workers during the Depression-era construction of the dam.

But the methods employed to put the bridge in place were borrowed from projects that date back to the 1800s, Petroski said. For example, the cable system that held the 1,060-foot concrete arch in place on the bypass span was the same method adopted by crews who built the Eads Bridge across the Mississippi River in 1874.

High-line cranes that lifted and moved heavy equipment, columns and concrete blocks around the canyon were similar to the cableway system workers used to build Hoover Dam, Petroski said.

"They had certain advantages; they were not using exactly the methods they did for the dam, but they were virtually identical," Petroski said. "More brute force was used back in the earlier times."


Petroski acknowledges that building the bypass bridge was a "world-class challenge" because of the steep canyon walls and rough terrain. He simply asserts that respecting the engineering phenomenon that is the Hoover Dam posed greater challenges for the engineers.

Dave Zanetell, the project manager of the bridge, recognized that early on.

"We are in the shadow of Hoover Dam," he said. "We are not only building a very tough civil works project, but we’re doing it in the shadow of the greatest civil engineering project ever created. It creates a heavy standard of responsibility."

Aesthetics are vital to communities adjacent to major projects such as bridges. In the San Francisco Bay Area, the Golden Gate Bridge is a must-see destination for tourists around the world. So when there were plans to expand its more utilitarian cousin, the San Francisco Bay Bridge, Oakland city officials fought for a design that approached that attractiveness of the Golden Gate.

"The Hoover Dam bridge is out in the middle of nowhere," Petroski said. "There are no cities so civic pride may or may not play the same role. Those who identify with the dam and see it as an engineering marvel, to them it was important how it looks."

A steel bridge might have been a less expensive option for the team of architects charged with designing the bypass, but it was never seriously considered because of concerns it would take away from the historic attraction. Petroski also said that at the time the bridge was being designed, only eight steel arch bridges existed in North America and only five spanned more than 1,100 feet.

The project management team settled on the concrete bridge because it best complimented the dam.

Hoover Dam is also an arched structure, so the arched bridge offers symmetry that might not be apparent to the average observer.

Even the location of the new bridge was debated. One proposal called for a span over Lake Mead, but concerns about trucking accidents causing hazardous materials to spill into the region’s water supply quashed that idea.

Building it farther downstream near Davis Dam was discussed but ultimately rejected because, among other reasons, of the longer, circuitous route.


The federal government identified a need to improve Highway 93 near the dam 40 years ago. But the project didn’t start to move forward until the mid-1990s when it was listed as a high priority corridor in the National Highway System Designation Act of 1995 and designated a part of the North American Free Trade Agreement route.

The highway was considered dangerous because of the increasing number of vehicles passing along it and the sharp switchbacks on the approach to the dam.

Since the Sept. 11, 2001, terrorist attacks, tractor-trailers have been prohibited from crossing the dam, instead traveling nearly 30 miles out of their way through Laughlin. Before the restrictions, 14,000 trucks and vehicles crossed the dam each day, according to the Federal Highway Administration.

In early 2005, construction finally began on the bypass bridge, which was formally named the Mike O’Callaghan-Pat Tillman Memorial Bridge. O’Callaghan was a decorated Korean War veteran who served as Nevada’s governor from 1971 to 1979. Tillman, who left his pro football career with the Arizona Cardinals to serve as an Army Ranger, was killed by friendly fire in Afghanistan.

As the bridge was being built and trucking restrictions across the dam remained in place, commuters might have been pleased they didn’t have to share the road with tractor-trailers, even if the security checkpoints and construction often tied up traffic crossing the dam.

But the restrictions impacted every consumer in the state, according to Paul Enos, chief executive officer of the Nevada Transport Association. Higher fuel and transportation costs were blamed for the increase in the price of fruits and vegetables in recent years, Enos said.

"When 90 percent of our manufactured goods arrive exclusively by truck, then you see an impact," Enos said. The detour "has absolutely had an impact on our industry."

"Truckers are going to take the route that is most efficient in time and money and operations and that is the new bridge."

The bridge is expected to trim some 45 minutes off the drive to Kingman, Ariz., although with delays that have plagued motorists for the past two years, the amount of time saved might actually be more than an hour.

Quicker travel times are also expected to open the door to new developments — bedroom communities to Las Vegas in Arizona just south of Hoover Dam — should the economy turn around.

As the construction of the bypass bridge progressed, development companies began marketing White Hills, just across the border in Arizona, saying that residents of equestrian communities just off Highway 93 could make it to the Strip in an hour.


It’s no secret that winds tear through the gorge. If that was ever in doubt, gusts of more than 50 mph toppled a high-line construction crane working on the bridge in 2006.

The bridge is designed to withstand 100 mph winds.

But tractor-trailers and high-profile vehicles will be prohibited from crossing the bridge when meters installed on and around the span clock sustained winds at 40 mph hours or gusts up to 50 mph, according to Mary Martini, district engineer for the Nevada Department of Transportation. Truckers will be warned of the restrictions via digital messaging signs posted 100 miles away in Utah, California and Arizona, allowing them ample time to choose an alternate route.

Enos said he anticipates that truckers — and vehicles hauling trailers — will face high-wind restrictions about 26 days out of the year.

Recent tests showed that the 54-inch solid concrete barrier on either side of the bridge protects cars from high winds. Martini said when gusts push against the concrete, they shoot upward away from traffic.

"Regular vehicles will always be able to go across the bridge," she said. "They will be protected because they are lower than the bridge rail."

The barriers also should ease the anxiety of drivers afraid of heights. The guard rails are so high that motorists crossing the bridge will not even know when they are crossing the gorge, Martini said.

Those guardrails are also designed to keep curious motorists from slowing down to take a peek of Hoover Dam. In order to see the dam from the bridge, drivers must exit on the Nevada side, where a new parking lot and interpretive path has been constructed. Pedestrians will be able to walk along the upstream side of the bridge, which offers a spectacular view of the dam.

"The original design had no walkways at all," Martini said. "Adding width to a bridge is costly."


Once the bypass bridge opens to traffic, Hoover Dam will no longer be accessible from the Arizona side.

Visitors coming from Arizona will have to cross the bypass bridge and take the existing road to the dam’s visitor’s center.

The question is what will happen to visitation numbers at Hoover Dam: Are tourists drawn to the dam to appreciate the engineering and take in the impressive view of Black Canyon? Or do they go to the dam because it is the primary route from Arizona to Las Vegas?

"Hoover Dam was always meant to be a tourist attraction. The minute it got under way the government was selling it as a tourist attraction," said Dennis McBride, curator of collections and history for the Nevada State Museum in Las Vegas. "This will certainly have an impact.

"I think a lot of people have gotten to the dam, seen what the traffic is like and just pulled off and hung around until it lightened up."

Visitors will be permitted to park at the visitor’s center or drive across to the Arizona side and park. But there will no longer be a through road. A marked exit from U.S. 93 will guide motorists to the dam on the north side of the bridge.

"Getting to the dam will be more of a chore," McBride said. "I definitely think the tourist numbers will go down. People are on the way from here to there; they aren’t going to stop."

Contact reporter Adrienne Packer at apacker@reviewjournal.com or 702-387-2904.

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