IOWA CITY — Passers-by may have noticed inspection crews surveying the underside of several Iowa City bridges this week using a snooper truck — which works similarly to a cherry picker, but with an arm that can reach down below a span.

Brett Zimmerman said inspections must take place every two years to ensure safety and meet state and federal bridge rules. With Iowa consistently finding itself near the top of the list for structurally deficient bridges, inspections become all the more important.

It was too early to say Monday if any of the city’s main bridges were in need of repairs, but Zimmerman said the city tries to keep ahead of any demand for repairs or updates. The city’s Prentiss Street Bridge is scheduled for replacement next year.

“We like to stay on top of things. I can’t speak for the rest of Iowa, but here locally, I don’t see us having the same statewide issue of being overwhelmed with poor bridges,” Zimmerman said.

While nationwide reports have often placed Iowa near the top of the list when it comes to the most structurally deficient bridges, a new report released this month by InsuranceQuotes finds Iowa ranks particularly well in a different category — functionally obsolete bridges.

The difference in ranking comes down to the definition.

A structurally deficient bridge has deterioration, cracks or other flaws that potentially reduce the load-carrying capacity and cause the need for weight restrictions.

Functionally obsolete bridges are constructed in a way that no longer meets modern design practices.

“Functionally obsolete might be related to geometry, meaning that at the time it was built it was a width that was a standard that served the purpose of the day, but now current design standards might require us to have wider lanes or shoulders,” said Jim Nelson, director of the Office of Bridges and Structures with the Iowa Department of Transportation.

Neither a functionally obsolete bridge nor a structurally deficient bridge is inherently dangerous.

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According to the InsuranceQuotes report, Iowa ranks third in the nation regarding the lowest percentage of obsolete bridges with 4.3 percent. Only Minnesota and South Dakota ranked better.

However, Iowa ranked first in the nation in terms of the total number of deficient bridges and second for the percentage of deficient bridges in a state’s overall inventory, according to a 2016 National Bridge Inventory report — released earlier this year — by the American Road and Transportation Builders Association, which uses Federal Highway Administration data.

In 2015, Iowa ranked third for the percentage of deficient bridges in a state’s overall inventory, but a 5.8 percent decrease in deficient bridges in Pennsylvania bumped Iowa into second place.

The number of structurally deficient bridges in Iowa dropped by 1.1 percent from 2015 to 2016.

All told, Iowa had 24,177 structurally deficient bridges last year, making up for 20.5 percent of all bridges in the state, according to the report.

Richard Pratt / The Gazette

But the state has many more bridge projects planned, said Laura Adams, senior insurance analyst with InsuranceQuotes.

“There’s a pretty high percentage, over 31 percent, looking at replacement, which I thought was interesting. It means the leadership in Iowa is likely very aware of what’s going on with the state of these bridges and there are proposals to replace them or repair them,” Adams said.

In addition, the InsuranceQuotes report found that Iowa’s structurally deficient bridges see some of the lowest levels of traffic.

According to the report, Iowa ranked second in the nation in fewest daily crossings over structurally deficient bridges with 271 crossings.

“The bridges in Iowa that were deficient are the least busy,” Adams said.

Of the more than 4,100 bridges in Iowa’s primary system, which includes interstates and highways, only 51 were considered structurally deficient this year.

Meanwhile, nearly 5,000 of the roughly 18,800 secondary system bridges — those in the counties — in the state are structurally deficient.

“The majority of traffic is on the primary system,” Nelson said.

Tom Rielly, a member of the Iowa Transportation Commission, which develops the state plan and policy for transportation needs and policies, said vehicle traffic is one factor considered when prioritizing bridge projects.

“Obviously, if we have a high traffic area, we want to make sure the bridges are in good shape,” he said. “However, in an extremely low traffic area, we do want to make sure those bridges are still safe.”

What’s the difference?

Wondering what the difference is between bridges that are structurally deficient vs. functionally obsolete? We’ve got you covered:

• Structurally deficient — Bridges have deterioration, cracks or other flaws that reduce the load-carrying capacity and cause the need for weight restrictions.

• Functionally obsolete — Bridges are constructed in a way that no longer meets modern design practices.

l Comments: (319) 339-3175; mitchell.schmidt@thegazette.com