Civil Engineering Reference
In-Depth Information
achieving current standards may put the bridge in the obsolescent category
while adding only marginally to the danger of travel. Then again, we have
to keep in mind that the country's stock of bridges has grown. Even if the
percentage
of obsolescence remains steady, the
number
of such bridges has
grown.
As we have seen, traffic is growing apace in cities and suburbs, espe-
cially in the largest metro areas. The demand does not necessarily have to
be met with more bridges. Public transit, better traffic management, and
incentives to get out of the car can reduce congestion while avoiding the
expense of new structures. But we should not be too sanguine about pos-
sibilities for reducing car dependence. Energy crises and fuel-price spikes
have come and gone, yet Americans have kept on driving.
Under the combined pressures of obsolete infrastructure and grow-
ing traffic demand, states and localities have continued to build new and
rehabilitate old bridges. The NBI registers about 8,000 bridge completions
per year in the United States, of which about 20 percent are rehabilita-
tions and the rest are newly built or replaced, as shown in table 2.6. As
we see in the table, rehabilitations have remained fairly level (with a peak
in 2009), but new builds have been declining. With over 144,000 deficient
bridges in America (of which 47 percent are structurally deficient and the
rest obsolescent), we're chipping away at about 8,000 per year.
Additional bridges join the deficiency list each year, so we are always
trying to catch up. And as the bridge stock from the 1960s comes due,
the deficiency list will grow unless the United States accelerates the rate
at which it builds new bridges. We are not in a bridge infrastructure crisis
now, but it is around the corner.
Table 2.6. Bridge Building by Year
New and Replaced
Rehabilitated
Total
2003
6641
2951
9592
2004
6504
1664
8168
2005
6130
1758
7888
2006
6182
1688
7870
2007
5334
1749
7083
2008
5364
1601
6965
2009
5368
2736
8104
2010*
4061
2421
6482
Source:
National Bridge Inventory
*Incomplete data
