Iowa has fewer structurally deficient bridges than it did two years ago, but still tops all other states in having the most in the latest inventory of the nation’s bridges.
A 2015 National Bridge Inventory report by the American Road and Transportation Builders Association — which uses Federal Highway Administration data — found that Iowa ranks first in terms of the total number of deficient bridges and third for the percentage of deficient bridges in a state’s overall inventory.
Of Iowa’s 24,242 bridges, 5,025 of them — or nearly 21 percent — are considered structurally deficient, according to the report.
Steve Gannon, Linn County engineer, attributed part of that ranking to the sheer number of bridges.
“It would be nicer if our bridge stock were in better condition, but part of the problem is Iowa just has lots of roads and lots of drainage so it has lots of bridges,” he said.
But just what is a structurally deficient bridge — and how concerned should motorists be in crossing them?
The highway agency declares a bridge structurally deficient when one or more of its key elements — such as the deck, superstructure or substructure — are in poor condition or worse.
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“They’re not an inherent danger to the traveling public, but it’s an indication that there are repairs that need to happen to the bridge,” said Alison Black, chief economist with American Road and Transportation Builders Association.
Norm McDonald, director of the Iowa Department of Transportation Office of Bridges and Structures, said a structurally deficient bridge can have deterioration, cracks or other flaws that reduce the load-carrying capacity and cause the need for weight restrictions.
“It’s not an unsafe bridge,” he said. “Structurally deficient bridges can continue to serve traffic safely if they are properly inspected and maintained.”
McDonald said 2,668 of Iowa’s bridges have posted weight limits.
But significant efforts are being made. Since 2011, the state has reduced its stock of deficient bridges by more than 400 statewide.
Bridges maintained by the state have dropped from 187 deficient structures in 2010 to 77 this year, McDonald added.
“We’ve had a concentrated effort to identify structurally deficient bridges and get them on the replacement list,” he said. “Over the last five or 10 years the system has been slowly shrinking. The really difficult thing to do is predict how many additional structurally deficient bridges we’ll have.”
Of Linn County’s 258 bridges, Gannon said 18 are structurally deficient or functionally obsolete. Eight of them bridges are slated for work this year, he said.
The builders assocation’s Black pointed to ramped up bridge repair efforts in recent years in Pennsylvania, which helped the state improve it ranking.
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“There’s definitely been a correlation over the last 15 years, as states are spending money, that number of deficient bridges is coming down, but it takes time,” she said. “We’re not investing at a rate to make this go faster.”
But there are other factors to keep in mind when looking at Iowa’s placement on the list. Iowa ranks seventh in the country for its total number of bridges and third per capita with only 129 people per bridge.
Those numbers factor into per capita funding sources such as the Road Use Tax Fund. But lawmakers gave it boost last year with a 10-cent fuel tax increase, which is expected to generate more than $200 million annually to help address a yearly shortfall in money to address critical upgrades to the state’s roads and bridges.
“There’s fewer of us to share the cost of our bridge stock,” Gannon said.
Gannon said it also comes down to priority — county governments are weighing bridge needs against road needs and sometimes roads are a higher priority.
“What the Legislature wanted to do with (the fuel tax) is speed up improvements to roads and bridges. Counties then have to figure out how to best spend it,” Gannon said.
Gannon said priority often goes to roads and bridges with higher traffic volumes.
“We replace those bridges more frequently than we would one serving a couple of fields because of the traffic volume, we inspect to ensure a level of safety, but essentially we’re not going to put the same level of effort into a bridge on a dead-end road, for example,” he said. “The system has lots of needs. The dime is going to be put toward, in Linn County anyway, the higher-volume roads.”