KVIG Informative

For nine years after the Sept. 11, 2001, terrorist attacks, every commercial truck crossing the Colorado River near Hoover Dam had to detour far out of its way, barred from the two-lane road running across the dam itself. The bridge that finally ended that detour cost $240 million, took roughly six years to build, and now carries the weight of protecting one of the country’s most recognizable pieces of infrastructure.

Federal security restrictions imposed after the Sept. 11, 2001, attacks barred commercial trucks from crossing the two-lane highway atop Hoover Dam, forcing freight traffic onto a lengthy detour, according to the Nevada Department of Transportation’s own published account of the project. NDOT separately noted that the dam-top road, never built to carry modern traffic volumes, was absorbing close to 5 million vehicle trips a year by the 2000s, far more than it could safely handle.

The Federal Highway Administration’s Central Federal Lands Highway Division began construction on a bypass bridge in 2004, according to NDOT. The project’s contractor, Obayashi-PSM Joint Venture, worked from designs led by engineering firms T.Y. Lin International and HDR Engineering, and closed the structure’s signature concrete arch in August 2009, according to a project account published by the American Segmental Bridge Institute, a professional engineering association that later recognized the project with an award.

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The finished structure spans 1,060 feet between its arch supports, rises roughly 900 feet above the Colorado River and stretches 1,900 feet in total length, according to NDOT’s published bridge specifications. NDOT describes it as the longest single-span concrete arch bridge in the Western Hemisphere; the American Segmental Bridge Institute ranks its main span fourth-longest among concrete arch bridges worldwide. Crews strung twin 2,500-foot cableways from 330-foot towers to move materials and equipment across the canyon, and placed most arch segments at night to keep curing concrete from overheating in conditions that reached 120 degrees Fahrenheit, according to the institute’s account.

More than 1,200 workers, engineers and other personnel worked on the span, according to NDOT. The bridge opened to traffic on Oct. 19, 2010, five days after a dedication ceremony attended by then-U.S. Transportation Secretary Ray LaHood, then-Federal Highway Administrator Victor Mendez, then-Senate Majority Leader Harry Reid, then-Rep. Dina Titus and then-Nevada Lt. Gov. Brian Krolicki, along with members of the Tillman and O’Callaghan families, according to NDOT’s account of the ceremony.

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Nevada and Arizona officials named the span the Mike O’Callaghan-Pat Tillman Memorial Bridge, after the former Nevada governor and the NFL player who was killed while serving with the U.S. Army in Afghanistan, according to NDOT, which describes that as the bridge’s official name. The American Segmental Bridge Institute gave the project its 2011 Bridge Award of Excellence in the long-span and cable-stayed category, citing its on-time, on-budget delivery and crediting the elimination of temporary post-tensioning during arch construction as a significant engineering savings.

Hoover Dam itself has not needed a security redesign since the bridge opened — the detour that once sent trucks far out of their way now runs over a quarter-mile of concrete arch instead, clear of the dam entirely. The bridge solved the problem planners identified after 2001. Whether the next threat to a 90-year-old dam looks anything like the one that justified a $240 million bypass is a bet Nevada and Arizona keep making every time a truck crosses that arch instead of the dam.