|
The Mike O'Callaghan–Pat Tillman Memorial Bridge is an arch bridge in the United States that spans the Colorado River between the states of Arizona and Nevada. The bridge is located within the Lake Mead National Recreation Area approximately southeast of Las Vegas, Nevada, and carries U.S. Route 93 over the Colorado River. Opened in 2010, it was the key component of the Hoover Dam Bypass project, which rerouted US 93 from its previous routing along the top of Hoover Dam and removed several hairpin turns and blind curves from the route. It is jointly named for Mike O'Callaghan, Governor of Nevada from 1971–1979, and Pat Tillman, an American football player who left his career with the Arizona Cardinals to enlist in the United States Army and was later killed in Afghanistan by friendly fire. As early as the 1960s, officials identified the US 93 route over Hoover Dam to be dangerous and inadequate for projected traffic volumes. From 1998–2001, officials from Arizona, Nevada, and several federal government agencies collaborated to determine the best routing for an alternative river crossing. In March 2001, the Federal Highway Administration selected the route, which crosses the Colorado River approximately downstream of Hoover Dam. Construction of the bridge approaches began in 2003, and construction of the bridge itself began in February 2005. The bridge was completed in 2010 and the entire bypass route opened to vehicle traffic on October 19, 2010. The bridge was the first concrete-steel composite arch bridge built in the United States,〔http://www.mtnmouse.com/nevada/hoover_dam_bridge.html〕 and it incorporates the widest concrete arch in the Western Hemisphere. At above the Colorado River, it is the second-highest bridge in the United States, following the Royal Gorge Bridge. It is also the world's highest concrete arch bridge.〔http://highestbridges.com/wiki/index.php?title=Mike_O'Callaghan-Pat_Tilman_Memorial_Bridge〕 The Hoover Dam Bypass project was completed within budget at a cost of $240 million; the bridge portion cost $114 million (2010 prices).〔 ==History== 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 by way of Las Vegas and Boulder City, crossing the Colorado River on the newly constructed Hoover Dam (also known then 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).〔(【引用サイトリンク】url=http://www.canamex.org/fed_def.asp )〕 This bridge is a key component of the proposed Interstate 11 project.〔 Through traffic on US 93 combined with pedestrian and tourist traffic at Hoover Dam itself led to major traffic congestion on the dam and on the approaches to the dam. The approaches featured hairpin turns on both the Nevada and Arizona sides of the dam, and the terrain caused limited sight distances around curves. In addition to traffic safety considerations, officials were also concerned about the safety and security of Hoover Dam, specifically the impact a vehicle accident could have on the dam's operation and the waters of Lake Mead. 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 1998–2001 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 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; commercial vehicles were required to follow a detour to a river crossing between Laughlin, Nevada and Bullhead City, Arizona.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mike O'Callaghan–Pat Tillman Memorial Bridge」の詳細全文を読む スポンサード リンク
|