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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Public Roads - July/August 1999

The Hoover Dam Bypass

by Terry Haussler and Doug Rekenthaler Jr.

More than 63 years after its completion, Hoover Dam remains one of the world's most impressive architectural and engineering triumphs. The dam is a National Historic Landmark and consistently ranks as one of the world's preeminent wonders of civil engineering. (See the article "Top Ten Construction Achievements of the 20th Century" on page 48.) Constructed in just four years (two years ahead of schedule) at the height of the Great Depression, Hoover Dam has become a magnet to those fascinated by human ingenuity at its best.

Traffic slows to a snails pace as it crosses the dam.

But increasingly, the dam is being plagued by its own success. Each day, thousands of visitors converge upon the dam, and every one of them is intent on peeking down at the canyon floor hundreds of feet below; gazing out at massive Lake Mead, which was created by the dam and stretches for as far as the eye can see; or learning more about the dam's massive hydroelectric turbines that feed electricity to power-hungry Las Vegas, Los Angeles, San Diego, and other growing western communities.

Complicating the picture are the thousands of interstate travelers -especially truckers -who are forced to use the lone highway in the region that has the unfortunate circumstance of traversing one of the country's most popular landmarks. U.S. Route 93 is a four-lane, blacktop highway that serves as a major connector between Arizona, Nevada, and Utah. It is one of only two such routes within 400 kilometers of the area.Additionally, much of Route 93 leading up to and over the dam narrows to two lanes, seriously compounding an already difficult traffic situation.

Environmental and wildlife concerns, including the habitat of bighorn sheep, were important factors in selecting the bypass route.

Travelers approaching the dam are quickly made aware of the glaring dichotomy that exists between the dam, which has tamed the mighty Colorado River and put its waters to use for man, and the highway leading to the dam, which remains at the mercy of the steep canyon walls within which the dam is nestled. Ironically, the traveler first must navigate a treacherous roadway that fails to meet most modern road design criteria before cruising across one of the world's great engineering wonders.

The heavy traffic has created innumerable headaches for travelers, truckers, and government agencies alike. Congestion along the three-kilometer stretch of highway leading up to and across the dam has raised concerns about air and noise pollution, dramatically affected the quality of the visitor's experience, and contributed to a growing number of accidents.

As traffic nears the bridge, speeds rapidly fall from 55 miles per hour (approximately 90 kilometers/hour) to 15 mi/h (25 km/h) as drivers begin to negotiate the sharp turns leading down into the canyon and across the dam. Many of the hairpin turns are too tight to accommodate large trucks, and taken in conjunction with poor line-of-sight visibility caused by the canyon walls, the sharp turns lead to numerous crashes involving tractor-trailers. In fact, of the approximately 500 crashes on or near the dam since 1964, nearly one-fifth involved trucks. And, in all of those cases, the cause was at least partly attributed to poor roadway geometries approaching the dam.


ppdamIn addition, Route 93 has been identified as a high-priority corridor in the National Highway System. It is the direct link between two of the fastest growing cities in the United States -Las Vegas and Phoenix -and it serves as a major north-south artery for commercial trade between the United States and Mexico.

Authorities are quick to point out that Hoover Dam is a major supplier of hydroelectric power to Southern California. Each year, the dam generates about 4 billion kilowatt-hours of electricity. A major accident on or near the bridge could affect the dam's power station and, in turn, have a profound effect on millions of residential and industrial power users.

And despite its reputation as a desert sea playground to pleasure boaters, sport fishermen, and vacationers, Lake Mead also serves as a vast water supply for southwestern cities, industries, and farmlands. A crash on Hoover Dam involving hazardous materials could seriously impact the quality of the water, and that would have an enormous impact on millions of people.

Finally, authorities would be remiss if they didn't take into consideration the very real specter of a terrorist strike against the dam.

All of which is to say that Route 93 leading up to and over Hoover Dam is a dangerous, overburdened bottleneck ripe for a major transportation disaster, and the dam's overseers and area transportation engineers would like nothing more than to create a high-speed bypass that would drain away from the dam all but sightseeing traffic.

The Search for a Solution

Beginning in the 1960s, the U.S. Bureau of Reclamation took the reins in hunting for a solution to the growing transportation difficulties at Hoover Dam. Working with officials from the Federal Highway Administration (FHWA) and the Arizona and Nevada departments of transportation, the Bureau of Reclamation periodically convened meetings to brainstorm possible ways to relieve congestion atop the dam. Those meetings ultimately resulted in a proposal to construct a new river crossing about 1.6 km south of the dam.

In 1989, the process took on new life when the Bureau of Reclamation established the Colorado River Bridge Project Management Team, which came to be known as PMT. Most of the major players remained the same, but they included a new face: the National Park Service, which had serious concerns about the environmental impact any proposed bypass would have on the fragile -and increasingly popular - ecosystem of the surrounding Mojave desert.

In fact, one of the biggest hurdles faced by bypass proponents was the need to mitigate any potential environmental impacts on the region. Hoover Dam is Black Canyon's most prominent denizen, but in the eyes of many environmentalists, not necessarily its most important. Despite the fierce desert conditions, the region is home to a plethora of wildlife, including bighorn sheep, bald eagles, peregrine falcons, and an array of game fish. As a result, Lake Mead is an increasingly popular destination for sport fishermen, pleasure boaters, hikers and campers, and other vacationers. Clearly, any proposed bypass would have to adhere to strict environmental regulations.

PMT's purpose was to address those environmental concerns as well as any engineering problems inherent in the bypass proposals. The team would also have to develop potential funding sources and manage the design and construction of the bypass.


Within a year of its formation, PMT had come up with three bypass proposals and a fourth "no-build" alternative, which essentially would put off the much-delayed project for further study. This last proposal was not seen as very likely unless the proposal met with severe resistance from environmental groups (who also are eager to alleviate the heavy traffic at the bridge) or a lack of funding. Other proposed plans were eliminated because of their high price tags, adverse impact on the environment, or unsatisfactory bridge foundations.

Bypass proponents were certain that any of the PMT proposals would effectively reduce traffic on the dam. The three proposals were:

  • Promontory Point. This alternative would include a 5.8-km stretch of new highway (4.3 km in Nevada, 1.5 km in Arizona) and a 670-meter cable-stayed or steel truss rib-through-arch bridge about 300 meters upstream of Hoover Dam. The estimated cost of the project is $204 million. The environmental impact of this proposal would be minimal.
  • Sugarloaf Mountain. This alternative would include a 5.3-km stretch of new highway (3.5 km in Nevada, 1.8 km in Arizona) and a 580-meter steel arch or cable-stayed bridge 460 meters downstream of Hoover Dam. The estimated cost of the project is $198 million. Of all the proposals, Sugarloaf Mountain poses the fewest environmental problems.
  • Gold Strike Canyon. This alternative would include a 5.3-km stretch of new highway (3.5 km in Nevada, 1.8 km in Arizona) and a 520-meter steel arch or concrete deck arch bridge about 1.6 km downstream of Hoover Dam. The estimated cost of the project is $215 million. This proposal poses the most significant environmental problems, including significant increases in noise and the largest impact in terms of affected acreage.

Unfortunately, just as PMT was picking up steam and finally appeared on the verge of moving forward with a Hoover Dam Bypass design proposal, potential funding streams for the environmental impact study dried up, and the mission of the Bureau of Reclamation - under whose auspices the PMT operated - changed. Just prior to release of the 1993 Draft Environmental Impact Statement for the PMT bypass proposals, the Bureau of Reclamation essentially switched its focus from construction of major public works to water resource management. Suddenly, the bypass movement was like a ship without a rudder (unable to steer the course) or the fuel (funds) to keep it going.

Bypass Over Troubled Waters

With the Bureau of Reclamation removed from the picture and no funding stream available for additional environmental studies, the project found itself adrift. In 1995, the Hoover Dam Bypass project officially was placed on hold.

However, after a decades-long wait, the impetus for action simply was too great. Traffic congestion at the dam was worse than ever, and authorities were convinced that a major catastrophe involving hazardous materials was inevitable unless interstate and international traffic could be diverted from the dam.

In early 1997, state and federal leaders from Nevada and Arizona appealed to U.S. Department of Transportation (DOT) Secretary Rodney Slater for funding assistance to complete the environmental impact studies on the bypass alternatives. DOT acknowledged the importance of the project, and with federal and state funds, the study was continued. In May 1997, FHWA's Central Federal Lands Highway Division was named as the lead agency to resume the Hoover Dam Bypass project.

As with any project of this magnitude, the move to create a Hoover Dam Bypass is not without its critics. Two alternatives that were dropped by PMT still have vociferous fan clubs.



Many residents of Boulder City, Nev., are in favor of the Willow Beach alternative, which essentially would remove trucks and through traffic from their town. However, many of the town's businesspeople are less enthusiastic about that plan, reasoning that the removal of this traffic could dry up a lot of potential commerce in the city.

This alternative was dropped because it would require the construction of 36 km of new highway approaches in Nevada and Arizona, most of it in the Lake Mead National Recreation Area, which constitutes a section 4(f) impact under DOT regulations. As a result, this proposal proved more expensive and damaging to the environment than other proposals on the table.

A proposal that has received strong backing from the Sierra Club is the Laughlin-Bullhead City alternative, which would use existing roads and possibly eliminate the need to eventually widen 23 km of Route 93 in the Lake Mead National Recreation Area just east of Hoover Dam. Environmentalists favor this route because it would use portions of U.S. Route 95, Nevada state Route 163, and Arizona state Route 68 to create a four-lane highway capable of accommodating interstate traffic. In addition, a multispan bridge would be constructed over the Colorado River between Davis Dam and the existing Laughlin Bridge.

In the eyes of most bypass proponents, however, the Laughlin-Bullhead City alternative has one major flaw. It essentially forces interstate and commercial traffic to take a 37-km detour around the dam. Under normal driving conditions, this might not seem particularly prohibitive; however, 27 km of this additional roadway is plagued by steep grades, which are problematic to the truckers and other interstate traffic the bypass is intended to serve. As a result, PMT dropped the Laughlin-Bullhead City alternative.

Where We Stand Now

FHWA is proceeding with the Final Environmental Impact Statement (FEIS), which is scheduled to be completed this summer.

In September 1998, the Draft Environmental Impact Statement (DEIS) for the bypass project was completed C with the cooperation of the Nevada and Arizona departments of transportation, the National Park Service, the Bureau of Reclamation, the U.S. Army Corps of Engineers, the U.S. Coast Guard, and the U.S. Fish and Wildlife Service C and it was distributed to interested parties for comment. Public hearings were held in October in Boulder City and Las Vegas, Nev., and Kingman, Ariz. On Nov. 10, the comment period ended, and PMT officials now are incorporating those comments into the FEIS.

FHWA is pursuing the Sugarloaf Mountain alternative. In December 1998, PMT selected this alternative for several reasons. In the DEIS process and public hearings, it received the most support from the public and from local, state, and federal agencies. It has the least environmental impact C impacting less desert bighorn sheep habitat and less desert tortoise habitat than the other two alternatives and having no impact on Lake Mead and the drinking water supply for southern Nevada. It has the best engineering, operational, and safety features with less than a kilometer of grades exceeding 5 percent (compared to more than four km of steep slopes for the Gold Strike Canyon alternative) and without curves at the ends of the bridge (other alternatives have curves at both ends). Also, it is the least expensive alternative.

Prior to completing the FEIS for the Sugarloaf Mountain alternative, FHWA will coordinate with the Fish and Wildlife Service and the offices of historic preservation in Arizona and Nevada to prepare mitigation plans for any adverse impacts to wildlife and cultural resources, including the Hoover Dam National Landmark. For example, some of the mitigation plans will limit construction to periods that minimize the effect on habitat used for migration or mating, replace any lost habitat, include erosion control and storm water runoff plans during construction and for long-term operations, and ensure that the design of the bridge is compatible with the historic setting of the dam. In addition, FHWA is working with the Western Area Power Administration to identify and minimize any potential effects on the power distribution system, and FHWA is consulting with Native American Indian tribes to address their concerns about the project.

Funding for the construction of the Hoover Dam Bypass remains a major hurdle. In 1998, Congress, through the Transportation Equity Act for the 21st Century (TEA-21), provided $41 million for the bypass. Another $4 million is being provided from Federal Lands Highway funds. Arizona and Nevada are committed for $10 million each. Each year, these states will apply for funding from two federal discretionary programs: the National Corridor and Development Program and the Federal Lands Highway Program. Funds from these two programs are allocated on a year-by-year basis and may not be sufficient to fund the entire balance needed for construction.

The estimated cost for design, engineering, and construction of the Sugarloaf Mountain alternative is $198 million. To address the $133 million shortfall, Arizona and Nevada are conducting a financial feasibility study to evaluate alternative funding mechanisms, including tolls, and to develop a financial plan. This study will be completed in summer 1999.

After comments on the FEIS are received and evaluated, a Record of Decision will be issued to officially announce FHWA's course of action. Assuming all funding requirements are met and any last-minute environmental issues are adequately addressed, final design work can begin this fall. The design of the roadways and bridge will take two to three years, allowing construction to begin in 2002. The bypass should be completed by the year 2007.

Although the new bridge will have its critics -especially those who will argue that the bridge mars dam visitors' views of Black Canyon -the bypass ultimately will improve traffic flow, substantially reduce air and noise pollution, effectively eliminate the threat of a serious accident on or near Hoover Dam, and dramatically improve the visitor's overall experience.

Terry Haussler is the EIS manager for the Hoover Dam Bypass Project. He has worked for the Central Federal Lands Highway Division of FHWA in Denver, Colo., for 19 years. His experience with Federal Lands includes project management, highway design, and construction. He has a bachelor's degree in civil engineering from North Dakota State University and is a registered professional engineer in Colorado.

Doug Rekenthaler Jr. is a freelance writer and editor. His experiences as a writer and editor include cub reporter covering Capitol Hill and Pentagon news beats; managing editor responsible for 12 newsletters that covered a wide array of communications technologies; founder of the multimedia industry's first daily fax news service; and corporate communications manager for America Online Inc., the largest commercial online service in the world.