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}} Navajo Bridge crosses the Colorado River's Marble Canyon near Lee's Ferry in the US state of Arizona carrying U.S. Route 89A. Spanning Marble Canyon, the bridge carries northbound travelers to southern Utah and to the Arizona Strip, the otherwise inaccessible portion of Arizona north of the Colorado River, which includes the North Rim of Grand Canyon National Park. Prior to the construction of the first Navajo Bridge, the only river crossing from Arizona to Utah was at nearby Lee's Ferry, where the canyon walls are low and getting vehicles onto the water is relatively convenient. The ferry offered only unreliable service, however, as adverse weather and flooding regularly prevented its operation. ==History== Construction of the original Navajo Bridge began in 1927, and the bridge opened to traffic in 1929. It was paid for by the nascent Arizona State Highway Commission (now the Arizona Department of Transportation) in cooperation with the United States Department of the Interior's Bureau of Indian Affairs, as the eastern landing is on the Navajo Nation. The steel spandrel bridge design was constructed by the Kansas City Structural Steel Company. During construction, worker Lane McDaniel died after falling to the Colorado River below. Supervisors had rejected the idea of rigging safety netting, believing that it would catch on fire from falling hot rivets. The bridge is in length, with a maximum height of from the canyon floor. Its roadway offers an surface width with a load capacity of 22.5 tons (although the posted legal weight limit was 40 tons). During the design phase, a wider roadway was considered, but ultimately rejected, as it would have required a costly third arch to be added to the design, and the vehicles of the time did not necessitate the wider road. In 1990, however, it was decided that the traffic flow was too great for the original bridge, and that a new solution was needed. The sharp corners in the roadway on each side of the bridge's approach had become a safety hazard due to low visibility, and the deficiency in the original design's width and load capacity specifications were becoming problematic. The bridge had also become part of U.S. Route 89A. Deciding on a solution was difficult, due to the many local interests. Issues included preservation of sacred Navajo land, endangered plant species in Marble Canyon, and the possibility of construction pollution entering the river. The original proposal called for merely widening and fortifying the bridge, but this was ultimately rejected since this could not possibly bring it up to current federal highway standards. Replacement was then the only option, and it was eventually decided to entirely discontinue automobile use of the original bridge. A new bridge would be built immediately next to the original and have a considerably similar visual appearance, but would conform to modern highway codes. The new steel arch bridge was commissioned by the Arizona Department of Transportation and the Federal Highway Administration, and was completed in September 1995, at a cost of approximately $15 million. The original Navajo Bridge is still open to pedestrian and equestrian use, and an interpretive center has been constructed nearby to showcase the historical nature of the bridge and early crossing of the Colorado River. Bungee jumpers are frequently seen using the span. The original bridge has been designated as a Historic Civil Engineering Landmark. The bridge was placed on the National Register of Historic Places on August 13, 1981.〔 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「Navajo Bridge」の詳細全文を読む スポンサード リンク
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