The latest federal report finds that Iowa still leads the nation when it comes to structurally deficient bridges.
The American Road and Transportation Builders Association’s 2019 Bridge Report, which uses Federal Highway Administration data, found that 4,675 — more than 19 percent — of Iowa’s bridges are classified as structurally deficient, meaning they are in need of some form of repair.
However, Scott Neubauer, bridge maintenance and inspection engineer with the Iowa Department of Transportation, added that only 39 of those bridges are part of the state highway system, compared to more than 230 bridges a decade ago.
“We aren’t having a big issue with them at the DOT,” Neubauer said. “We have been eating away at that for the last 10 years.”
The vast majority of Iowa’s structurally deficient bridges are rural, low-traffic bridges. Of the more than 4,000 county bridges on the list, the median traffic volume is 35 vehicles a day, he added.
With such low traffic volume and bridge repairs or replacements often expensive, Neubauer said it’s a challenge for local entities to find the money to fix aging bridges.
All told, 4,675 of Iowa’s 24,123 bridges were deemed structurally deficient, putting Iowa at the top of the list with the largest number of structurally deficient bridges in the nation. Iowa ranks third with the percentage of structurally deficient bridges in the state inventory.
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“While these bridges may not be imminently unsafe, they are in need of attention. Nearly 69,000 bridges across the country are ‘posted for load’ which means there are weight restrictions or other measures in place to reduce stress on the structure,” according to the American Road and Transportation Builders Association’s report.
Linn County Engineer Brad Ketels said 11 of the county’s 254 bridges are considered structurally deficient. The average age of all county bridges is 34 years old. The average age of the 11 deficient bridges is 101 years old. The typical life span of a bridge is 75 years, he said in an email to The Gazette.
“The majority of our bridges that are (structurally deficient) are by choice. These bridges are either on the historic register or are possibly eligible to be included on the historic register. Either way, we are exploring ways to have a plan in place for all of these bridges,” Ketels said.
One of those bridges, on Jordans Grove Road over the Wapsipinicon River southeast of Central City, is planned for replacement this year.
All told, Iowa has identified needed repairs on 15,350 bridges, estimated at $1.6 billion.
Of those proposed projects, 7,400 include complete bridge replacement.
According to the American Road and Transportation Builders Association report, two of the most traveled structurally deficient bridges in Iowa are in Johnson County — at Gilbert Street over Ralston Creek and the Burlington Street bridge over the Iowa River, both in Iowa City. The remaining most traveled structurally deficient bridges are in Scott, Polk, Woodbury and Poweshiek counties.
While last year’s bridge inventory marks a slight drop from the 4,805 bridges with that classification in 2017, some of that could be a little misleading following new Federal Highway Administration definitions that went into effect at the beginning of 2018.
Previously, a bridge could be considered structurally deficient if the overall structural evaluation rated the bridge in poor or worse condition.
A new definition only applies to bridges where one of the key structural elements — the deck, the superstructure, the substructure or culverts — are rated in poor or worse condition.
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With the new definition, more than 6,500 nationwide bridges rated structurally deficient in 2017 were no longer classified as such in the following year.
Iowa bridge figures
• Of the 24,123 bridges in Iowa, 4,675, or 19.4 percent, are deemed structurally deficient.
• Seven of those bridges are on the interstate highway system.
• 4,815 bridges are posted for load, meaning they may have restricted size or weight rules.
• The state has identified 15,350 bridges in need of repairs, estimated at $1.6 billion.
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