Mike O'Callaghan–Pat Tillman Memorial Bridge

In 1935, the American Association of State Highway Officials (AASHO, later AASHTO) authorized a southward extension of U.S. Route 93 from its previous southern terminus in Glendale, Nevada to Kingman, Arizona via Las Vegas, Boulder City, and a crossing of the Colorado River on the newly constructed Hoover Dam (then known as Boulder Dam). Clark County was sparsely populated at the time, with a population of less than 9,000 at the 1930 U.S. Census (compared to an estimated 2 million in 2013). Development in and around Las Vegas in the latter half of the 20th century made Las Vegas and its surrounding area a tourist attraction, and US 93 became an important transportation corridor for passenger and commercial traffic between Las Vegas and Phoenix. In 1995, the portion of US 93 over Hoover Dam was included as part of the CANAMEX Corridor, a high-priority transportation corridor established under the North American Free Trade Agreement (NAFTA). This bridge is a key component of the proposed Interstate 11 project. Officials first discussed the need for a new Colorado River crossing that would bypass the dam in the 1960s. The U.S. Bureau of Reclamation, which operates the dam, began work on the "Colorado River Bridge Project" in 1989, but the project was put on hold in 1995. In 1997 the Federal Highway Administration took over the project and released a draft environmental impact statement in 1998. From 1998 to 2001 state officials from Arizona and Nevada as well as several federal government agencies studied the feasibility of several alternative routes and river crossings, as well as the feasibility of modifying the roadway over the dam, restricting traffic over the dam, or doing nothing. In March 2001, the Federal Highway Administration issued a Record of Decision indicating its selection of the "Sugarloaf Mountain Alternative" routing. The project called for approximately of highway in Nevada, of highway in Arizona, and a bridge length of that would cross the river downstream (south) of Hoover Dam. Design work began in July 2001. Security measures implemented following the September 11 attacks prohibited commercial truck traffic from driving across Hoover Dam. Prior to the completion of the bridge, commercial vehicles were required to follow a detour between Boulder City and Kingman via US 95, Nevada State Route 163, the Colorado River crossing between Laughlin, Nevada and Bullhead City, Arizona, and Arizona State Route 68. The detour was long, but only added to the normal journey on US 93. ==Design==

Project design was by the Hoover Support team, led by HDR, Inc. and including T.Y. Lin International, Sverdrup Civil, Inc., and other specialist contributors. The bridge has a length of and a span. The roadway is above the Colorado River and four lanes wide. This is the first concrete-and-steel composite arch bridge built in the United States. It includes the widest concrete arch in the Western Hemisphere and is also the second highest bridge in the nation, with the arch above the river. The twin arch ribs are connected by steel struts. The composite design, using concrete for the arch and columns with steel construction for the roadway deck, was selected for schedule and cost control while being aesthetically compatible with the Hoover Dam. Sean Holstege in The Arizona Republic has called the bridge "an American triumph". USA Today called it "America's Newest Wonder" on October 18, 2010. Pedestrian access is provided over the bridge to tourists who wish to take in a different view of the nearby dam and river below, but the dam is not visible for those driving across it. A parking area is provided near the bridge on the Nevada side at what was a staging area during construction. A set of stairs and disabled access ramps lead to the sidewalk across the bridge. ==Construction==

Work began in 2003 on the approaches in both states and the construction contract for the arch bridge was awarded in October 2004. The former US 93 route between the dam and its junction with the present US 93 route has been re-designated as Nevada State Route 172. The highway using the bridge was given the added designation of Interstate 11 in 2018, after the completion of the Boulder City freeway bypass. ==Naming==

In late 2004, the proposed bridge name honoring Mike O'Callaghan and Pat Tillman was announced at a ceremony by the Governor of Nevada, Kenny Guinn, and the Governor of Arizona, Janet Napolitano. O’Callaghan, a decorated Korean War veteran, was the Governor of Nevada from 1971 through 1979, and he was the executive editor at the Las Vegas Sun newspaper for many years until his death on March 5, 2004. Tillman had been a football player for Arizona State University and for the Arizona Cardinals. He gave up his multimillion-dollar career in the National Football League to enlist as an infantryman in the U.S. Army, and was killed by friendly fire in Afghanistan on April 22, 2004. ==Incidents==

Construction crane collapse Strong winds gusting across the Black Canyon on September 15, 2006, appear to have been the cause for the collapse of the "high-line" crane system that was used to carry workmen and materials at the bridge site. No injuries or fatalities occurred because of this accident. Limited construction work resumed in October 2006, but this accident caused a two-year delay in construction. The bridge-construction companies Obayashi Corp. and PSM Construction, USA, Inc. absorbed the cost of the debris removal and the rebuilding of the cranes. ==In popular culture==

• In the 2015 disaster movie San Andreas, the bridge is destroyed in a massive earthquake along with the Hoover Dam. ==See also==