Living up to a landmark: building a bridge that will overlook Hoover Dam—and enhance it—is a once-in-a-lifetime engineering challenge

Public Roads, March-April, 2003 by Norah Davis

Millions of people visit Hoover Dam every year to marvel at what is often called one of the engineering wonders of the world. They drive there on a highway that crosses the Colorado River on the crest of the dam. Just downstream from this national historic landmark, only 458 meters (1,500 feet) to the south, construction has begun on a new road and bridge over the river gorge. The new route will provide a bypass for through-traffic from Arizona to Nevada and relieve concerns about congestion, safety, and security on the existing highway.

The type study for the new bridge paints a striking word picture of the setting for the bypass: "The Black Canyon below Hoover Dam is a 244-meter (800-feet)-deep gorge carved by the Colorado River through a rugged, hard rock landscape forged by eons of geologic transformations."

Tourists walking on the crest of Hoover Dam and boaters upstream on Lake Mead will see the new bridge soaring across this dramatic canyon. Visitors downstream strolling across the new bridge's pedestrian walkway will have an equally breathtaking view of the dam.

Since its construction 70 years ago, Hoover Dam has been recognized internationally as the standard of excellence in dam design. As the type study states, "Hoover Dam is a [magnet] for millions of visitors in large part because the designers and builders of the Dam expressed an art for engineering that went beyond the austere and functional."

No pressure here for the new bridge's designers and builders--all they have to do is create a span that will frame Hoover Dam for future generations with the same grandeur, elegance, and grace.

A Partnership for Safety, Mobility, and The Environment

The Federal Highway Administration's (FHWA) Central Federal Lands Highway Division is the lead agency for the bypass project in a multiagency cooperative effort by the Arizona and Nevada departments of transportation (DOTs), the National Park Service, Western Area Power Administration, and the Bureau of Reclamation. Nearby communities, Native American tribes, and individual citizens are taking active roles as well. The diverse range of groups makes the bypass project truly a multiple stakeholder partnership.

Construction of this historic project is now underway. At the bridge's groundbreaking ceremony on October 21, 2002, FHWA Administrator Mary E. Peters spoke from the observation deck of the Hoover Dam Visitors Center. After mentioning that she worked on the Hoover Dam Bypass project for many years as director of the Arizona DOT, well before she served as FHWA administrator, she continued, "At FHWA, we have three key priorities [saving lives, reducing congestion, and protecting the environment], and all three are represented in this project."

To address these vital few priorities, the new project will meet current roadway design criteria for safety, improve travel time for through-traffic, and reduce air pollution caused by the current congestion.

Saving Lives

The 5.6-kilometer (3.5-mile) section of U.S. 93 on either side of Hoover Dam has a crash rate three times that of the rest of U.S. 93. The two-lane highway is narrow, steep, and winding with switchbacks and hairpin curves. The roadway widths are inadequate, the sight distances poor, and the shoulders too narrow for traffic volumes that are double those of 15 years ago.

What's more, once the highway reaches the dam, pedestrians crossing the road to view the facility are at risk. The daily mix includes more than 3,500 pedestrians competing with 10,000 cars and 1,700 trucks for use of U.s. 93. As Dave Zanetell, FHWA project manager for the Hoover Dam Bypass, says, "The safety concerns are exacerbated by the fact that this facility is trying to serve two purposes, so that an unsafe blend of pedestrians and through-traffic exists. An estimated six million visitors a year walk on the deck of the dam, so you have a melee of people and traffic."

Fixing a Bottleneck

In her speech at the visitors center, Administrator Peters pointed out that traffic on the road sometimes backs up for more than 24 kilometers (15 miles), with motorists delayed by as much as 5 hours. U.S. is a major commercial route carrying traffic from Arizona to Nevada and Utah, connecting Phoenix and Las Vegas (our Nation's two fastest-growing cities over the past 10 years). In addition to interstate commerce, U.S. 93 is a designated North American Free Trade Agreement (NAFTA) route--a critical link carrying international commerce on the north-south CANAMEX corridor between Canada and Mexico.

"Hoover Dam itself was never intended to handle this type of traffic and traffic volume," says Zanetell. "Its use as a transportation facility simply evolved out of its original functions." As early as the mid-1960s, the Nevada DOT and Bureau of Reclamation began pursuing efforts to bypass the dam.

"The volume of traffic is such that, for nearly 3 hours out of every day," says Zanetell, "we can anticipate a minimum of a 30-minute or longer delay for motorists crossing the project site."