Environmental Engineering Reference
In-Depth Information
fatigue or other structural challenges. In addition to the dangers of design
inadequacies, the useful safe life of bridges has been shortened because
they carry far more vehicles per day than when they were built decades
ago. Compounding the problem is the fact that modern inspection tech-
niques were not available until recently. Modern bridge inspections use
ultrasound, wireless sensors, X-ray technology, and other techniques to
detect cracks, corrosion, and other defects.
The Interstate 35W bridge in Minneapolis that collapsed into the
Mississippi River in August 2007, killing 13 and injuring 145, was
built in 1967 and was one of 760 identically built bridges around the
country, 35 percent of which were found to be structurally defi cient
by the Federal Highway Administration in 2006. An examination of
bridges with a similar but not identical design revealed that 58 percent
were defi cient.
40
Seventy-three percent of road traffi c in the United States and 90
percent of truck traffi c travels over state-owned bridges.
41
States tend
to ignore bridge and road maintenance because if they wait until they
are in poor condition, they become eligible for federal funds (federal
funds cannot be used for routine maintenance). As noted earlier, the
federal Highway Trust Fund is now bankrupt.
Resurrecting Railroads
The fi rst railroad in the United States was chartered in 1826 in Massa-
chusetts and was 3 miles in length. It carried its fi rst passengers two years
later. By 1840, 2,800 miles of track had been laid, a number that
increased rapidly each decade, to peak at 254,000 in 1916. Since that
time, the number of miles of track has decreased continuously, in part
because of a concerted campaign by American carmakers to acquire rail
lines and close them, and in part because of a decision by Congress in
the 1950s to build the world's most extensive interstate highway network.
Today there are only 161,000 miles of railroad track, about the same
amount that existed in the late 1890s.
Despite the loss of track, freight railroad traffi c and freight volumes
have increased dramatically during the past forty years. Railroads today
are primarily high-volume freight haulers, accounting for more than 40
percent by weight of the nation's freight, carried in 1.3 million freight
cars. Almost half the freight is coal (fi gure 2.3).
Within the past few years, the rising cost of gasoline for eighteen-
wheel trucks has sparked an increased commercial interest in railroads
