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Top Ten: Bridges

“There is nothing in machinery, there is nothing in embankments and railways and iron bridges and engineering devices to oblige them to be ugly. Ugliness is the measure of imperfection.” ~H.G. Wells

1. Hoover Dam Bypass Bridge – Construction on the nearly 2,000 foot long bridge began in late January 2005. Strong wind gusts across the canyon on September 15, 2006 contributed to the collapse of four 280-foot tower cranes, which in turn brought down the cable supports and resulted in a two-year construction delay. Originally scheduled for completion in 2008, the entire project is expected to be finished by September 2010. U.S. 93 had been identified as a high priority corridor in the National Highway System Designation Act of 1995. Since 1936, the present route of U.S. 93 has used the top of Hoover Dam to cross the Colorado River. Today, U.S. Highway 93 is the major commercial corridor between the states of Arizona, Nevada, and Utah; it is also on the North American Free Trade Agreement (NAFTA) route between Mexico and Canada. The existing narrow 2-lane road with its inadequate shoulders, sharp turns, poor sight distance, and low travel speeds compounded by sightseeing and pedestrian traffic at the dam, often makes traffic come to a standstill. By developing an alternate crossing of the river near Hoover Dam, through-vehicle and truck traffic would be removed from the top of the dam. Additionally, in the wake of the September 11, 2001 terrorist attacks there have been significant security concerns. Because of the attack, the Hoover Dam Bypass project was expedited. Traffic across Hoover Dam is presently restricted, with commercial truck traffic diverted south to a Colorado River bridge at Laughlin, Nevada. However, this has not eliminated the threat of a possible attack on the dam, as regular traffic still passes over it. The bypass and the bridge are therefore intended to improve travel times, replace the dangerous roadway, and reduce the possibility of an attack or accident at the dam site. When completed, the bridge will span the Black Canyon about 1,600 feet south of Hoover Dam. Total length of the bridge is 1,900 feet with a 1,080-foot main span. The roadway will be 840 feet above the river. It will be the first concrete-steel composite arch bridge built in the United States, in which the arch is cast in place over the river rather than precast and put into place. That means that before ever starting to build the bridge, construction crews had to build temporary towers to support the growing arch using a specially designed cable system. In late 2004, the bridge was formally named the Mike O’Callaghan-Pat Tillman Memorial Bridge. (O’Callaghan was a decorated Korean War veteran and was governor of Nevada from 1971 to 1979. Tillman was an Arizona Cardinals football player who gave up his multimillion-dollar NFL career to enlist in the U.S. Army, and was soon after killed in Afghanistan.) Traffic finally began flowing over the Hoover Dam Bypass on October 19, 2010.

2. London Bridge – Arizona seems an unlikely destination for an old world relic, but the famous London Bridge of England is indeed the same bridge that now resides in Lake Havasu. Originally built in 1831, the bridge served as a crossing over the River Thames in London for more than 140 years. It survived both world wars and a terrorist attack. But in 1962, London Bridge really was falling down. The bridge began sinking into the clay beneath the river and needed to be replaced, a victim of its own immense weight. In 1968, the City of London sold it for 2.5 million dollars to Robert McCulloch, founder of Lake Havasu City. At the time it was the highest price ever paid for an antique. From 1968-1971 the bridge was dismantled block by block and its 10,276 pieces were reassembled in Arizona, at a cost of another $7 million. It was to be a tourist attraction for the new planned development. London Bridge connects Lake Havasu City with an island, crossing a narrow channel that was dug out from what was once a peninsula alongside Lake Havasu. At the base of the massive stone arch bridge is a one-acre English Village filled with quaint Tudor-style buildings and shops creating an atmosphere of Medieval England. The London Bridge visitors’ center contains some historic photos and other information.

3. Navajo Bridge – Navajo Bridge spans the Colorado River’s Marble Canyon near Lee’s Ferry. Apart from the Glen Canyon Bridge a few miles upstream at Page, it is the only roadway crossing of the river and the Grand Canyon for nearly 600 miles. Prior to the construction of Navajo Bridge, the only river crossing from Arizona to Utah was at nearby Lee’s Ferry, where the canyon walls are low. The ferry was unreliable, however, as adverse weather and flooding often prevented its operation. Construction of the original Navajo Bridge began in 1927, and the bridge opened to traffic in 1929. The steel spandrel bridge is 834 feet long, with a maximum height of 467 feet from the canyon floor. By 1990 the amount of traffic across the narrow (18 ft. wide) bridge was making it unsafe. Between 1993 and 1995, a new steel arch bridge was constructed alongside the original one. This one is 909 ft. long, 470 ft. above the river, and 44 ft. wide. The old Navajo Bridge is still open to pedestrians and it is sometimes used by bungee jumpers. The Navajo Bridge has been designated as a Historic Civil Engineering Landmark, and an interpretive center has been built nearby to showcase the historical nature of the bridge and early crossing of the Colorado River.

4. Glen Canyon Bridge – Completed in 1964, the Glen Canyon Bridge is 1,560 ft. long and 700 ft. above the Colorado River. It is the 4th highest bridge in the United States. Before it and the downstream Navajo Bridge were built, people had to drive 800 miles around the canyon to reach the other side of the river.

5. Gillespie Dam Bridge – Located 22 miles North of Gila Bend on Old Highway 80 at the Gila River, this historic bridge (also known as the Gila River Bridge) is one of the most important examples of early bridge construction in Arizona. Here at the site of an old stagecoach ford, autos could drive across the river unassisted during low water flow. During higher flows, cars had to be chained together and pulled across by a truck. When the Gila River flooded, traffic ceased altogether. In 1925, Highway Department engineers recommended the construction of a long-span steel truss bridge. The resulting bridge contains nine truss spans with 10 concrete piers. The nine trusses measure 1640 feet in length and total paved length is 1701 feet, with a clear width of 19 feet. Upon its completion, the Gillespie Dam Bridge became the state’s longest highway bridge and possessed the deepest foundations representing a breakthrough in Arizona bridge-building. It’s also the only suspension bridge in Maricopa County and one of very few in Arizona. As part of U.S. 80, the bridge was a component in the early transcontinental highway system. In almost unaltered condition since its construction in 1927, it is now closed and in danger of catastrophic failure. However, preservation efforts should enable the bridge to exist for many more years to come.

6. Sheep Bridge – The Old Verde River Sheep Bridge, also known as Red Point Sheep Bridge, was a cable suspension bridge built by local sheepherders so that they could move their flocks more easily across the river and gain access to the cooler mountain grazing in the summer months. It was made entirely by hand tools. No heavy machinery was used. The bridge was started in 1943 and finished in 1944 at a cost of $7,277. They obtained materials from a nearby mine and from a railroad line. On November 21, 1978, the Sheep Bridge was entered into the National Register of Historic Places. In 1988, the bridge was closed because it was weakened after years of service and floods. The old bridge was dismantled in 1989 and a new structure of similar design was put up in its place at a cost of over a million dollars. Sheep ranching is no longer carried out in the area, but the bridge is used by hikers, horseback riders, and hunters to gain access to the Mazatzal Wilderness. It’s located about 21 miles northeast of Cave Creek in the Bloody Basin area of the Tonto National Forest, where the Verde River makes a Z-shaped bend between two prominent rock outcroppings. (Caution: the last time we were there, a few of the wooden slats were missing and a small child could slip right through.)

7. Roosevelt Lake Bridge – This bridge is the longest two-lane, single-span, steel-arch bridge in North America. The bridge spans 1,080 feet across Roosevelt Lake. Prior to completion of the bridge in October 1990, traffic drove over the top of the dam. The Roosevelt Lake Bridge earned rare distinction when it was named one of the nation’s Top 12 bridges in November 1995. The American Consulting Engineers Council cited the bridge for overall design, size, eye-appeal and design challenge. Other bridges cited were the Golden Gate Bridge and Brooklyn Bridge.

8. Pinedale Covered Bridge – The road into Pinedale has the only real old-fashioned covered bridge in Arizona. It’s located just north of Pinedale, about a half mile from the junction of AZ60, crossing the Pinedale Wash. The wooden structure built in 1976 is 75 feet long and is named the Maureta B. Thomas Memorial Bridge.

9. Burro Creek Canyon Bridge – This beautifully shaped steel arch bridge over the pristine Burro Creek Canyon in Western Arizona was built in 1966 utilizing cantilevered construction and temporary cable-stays. In 2006, a new steel arch bridge in similar style to the original was erected alongside the existing Burro Creek Bridge, with a parallel roadway creating a four-lane divided highway between Wickenburg and Kingman. The existing bridge carries the southbound lanes of the highway. The new bridge which accommodates northbound traffic is 985½ feet long. Length of arch from pin to pin is 699 ft. 10 in. The roadway is 388 feet above Burro Creek. The new bridge is constructed of “weathering steel” which will not be painted, and will acquire a natural brown appearance. The canyon is over 1000 feet wide and 500 feet deep at the highway crossing. The location is environmentally sensitive, part of a wilderness recreation and campground area. Burro Creek which flows year-round is designated as “unique water” upstream of the bridge. The best location for crossing the canyon was already taken by the existing bridge. For the new bridge, weak rock had to be bolted and stabilized. Due to close proximity of the existing bridge, construction crews had to be extra careful in order to prevent accidental damage. An elliptical arch geometry was developed to maintain symmetry in the asymmetric canyon.

10. Mill Avenue Bridge – The concrete arch bridge over the Salt River on southbound Mill Avenue in Tempe was built in 1931. Over the years, the bridge survived many strong floods that raged through the Salt River Valley. In February 1980 all but two of the bridged crossings on the Salt River were closed for safety reasons due to severe flooding. The Mill Avenue Bridge and the Central Avenue Bridge in Phoenix were the only bridges that were structurally sound enough to remain open for carrying traffic from one side of the Valley to the other. Water hit the Mill Avenue Bridge at 200,000 cubic feet per second, which far surpassed the expected strength of the bridge. 92,000 vehicles crossed the two-lane bridge in one 24-hour period during the flood. In 1993, extensive flooding washed away the framing of the new Mill Avenue Bridge, which was then under construction directly to the east of the original bridge. The new bridge opened in 1994, allowing for two lanes to travel in each direction.

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