According
to a recent AP article, snarled traffic costs travelers 3.5 billion
hours a year in the 85 largest US cities. The average urban commuter
was stuck in traffic 46 hours a year, a large increase from 16 hours
of 20 years ago. In many places, the bottlenecks in traffic flow have
traditionally been, and continue to be bridges. The Federal Highway
administration database shows that Americans use almost 6000 bridges!
While we tend to take bridges for granted - after all they often simply
allow us to get from one place to another - American genius has come
to the forefront time and time again in finding solutions for some
very difficult crossings. Many of our bridges use quite different and
interesting construction techniques and some are beautiful works of
art!
As part of a $234 million bypass project for the Hoover Dam, construction
on The Colorado River Bridge begins in November. When completed in
2008 it will be the longest concrete arch in North America: 2000 feet
long, 890 ft high, 4 lanes wide, sited 1500 feet downriver from the
Hoover Dam. The Composite Concrete Deck Arch Bridge was chosen for
its utility, but also because it was considered architecturally compatible
with the dam.
The Hoover Dam Bypass Project (which includes the New Colorado Bridge)
is a complex project made up of four miles of roadway, eight bridges,
wildlife crossings, a 2,000 foot-long bridge over the Colorado River
and various pedestrian and visitor improvements. The Arizona side includes
the already constructed Sugarloaf Mountain Bridge – a 900-foot
bridge spanning a canyon on the east side of Sugarloaf Mountain. It
consists of 77 prestressed, 128 ft. long concrete box girders, which
weigh 66 tons each.
The project took a much higher priority after Sept. 11 because of
terrorist concerns. This resulted in closing the current route directly
over the dam to trucking. Detouring 2,100 trucks daily is estimated
to cost consumers $30 million annually. This summer Arizona and Nevada
each pledged $50 million in GARVEE bonds to keep the project moving – because
of the stalled federal TEA-21 funds. http://www.hooverdambypass.net
Cooper River Bridge - Charleston, South Carolina: When completed next
Spring, this will be the longest cable-stayed bridge in North America
with a main span of 1546 ft. A series of public meetings resulted in
choosing the final design. The ‘diamond’ towers reach 575
feet tall and support an 8-lane road deck 200 feet above high tide
with 128 cables. To protect them from weather conditions, the bridge
cables are enclosed in a high density polyethylene pipe. http://www.cooperriverbridge.org
Part of the Boston’s Big Dig, the Leonard P. Zakim Bunker Hill
Bridge is unique. With 10 lanes of traffic and 183 ft wide, it is the
widest cable-stayed bridge in the world, and the first “hybrid” cable-stayed
bridge in the United States, using both steel and concrete in its frame.
It is built in such a highly congested area that the engineers had
to come up with a unique design – it is supported by two inverted
Y-shaped towers which straddle the MBTA tracks at a 55-degree angle.
It is partially open to traffic and should be completed next year.
Completed in 1987, the Sunshine Skyway spanning the mouth of Tampa
Bay, is the world’s longest cable-stayed concrete bridge. It
is 29,040 feet long with the longest single span at 1200 feet. It replaced
a steel cantilever bridge which was severely damaged in 1980 by a freighter.
The new bridge links more than 300 precast concrete segments with high-strength
steel cables to form the roadway. Large concrete islands, called dolphins,
were created around each of the bridge’s six piers to absorb
accidental impact from ships.
With aging infrastructure, the Federal and State organizations face
a huge task. The FWHA stated goal is to replace and/or rehabilitate
at least 12,000 bridges per year. Funding for highways and bridges
continues to be at the stop-gap level in Congress. Transportation programs
have been operating under a series of five short extensions since Sept.
30, 2003, when TEA-21, the previous funding bill, expired. A House-Senate
conference to work out differences between a six-year $318 billion
Senate bill and a $284 billion House version was unsuccessful this
year. On September 30 Congress finally once again approved another
extension, which will continue federal highway and transit program
funding for another eight months - running through May of 2005.
In the Next Issue: Bridge Failures and Innovations
Return to Top
------------------------------
