By Katie Dahlstrom
Drivers are less likely to cross a deficient bridge in Clinton County than elsewhere in Iowa. But a recent report suggests they shouldn’t feel too comfortable.
While Clinton County has the least amount of structurally deficient bridges in Iowa, the state ranks as the third most deficient in the nation.
More than 21 percent of Iowa’s bridges are structurally deficient, according to a report from transportation lobby group Transportation for America. Of the 24,465 bridges in the state, 5,191 are deficient, which means they need to be repaired or more closely monitored.
The report was derived from the National Bridge Inventory, a compilation of state-collected data, which is reported to and then published by the Federal Highway Administration.
Clinton County was the best in Iowa with only 3.5 percent of its bridges rated structurally deficient. Jackson County ranked fifth out of 99 counties with 5.4 percent of its bridges structurally deficient.
The top five counties in Florida, Nevada and Texas, the states that fared the best in the report, have no structurally deficient bridges.
Being classified structurally deficient does not necessarily mean a bridge is unsafe, but it does require significant maintenance.
The city of Clinton maintains 32 bridges, of those three are deficient, according to City Engineer Jason Craft.
The bridge on West Deer Creek road is one of those structurally deficient pieces of infrastructure. Built in 1920, around 80 vehicles travel over the bridge daily.
Bridges are rated as structurally deficient based on the state of three components: the deck, which directly carries cars; the superstructure, which supports the deck; and the substructure, which supports the superstructure and connects to the ground.
According to Transportation of America, the West Deer Creek deck and superstructure earned a score of four out of 10. The substructure received a five out of 10.
The terms structurally deficient and functionally obsolete are used to classify bridges so they can be replaced using federal funding. The FHWA estimates it would cost $76 billion to repair the nation’s deficient bridges.
“West Deer Creek is on a federal list for potential replacement but it might not be too soon,” Craft said.
Transportation for America asserted the maintenance backlog will grow as bridges age, costs rise and revenues dwindle.
“With declining gas tax revenues for transportation and other budget woes, securing the money to repair or replace thousands of bridges, while fixing the other parts of our aging highway and transit networks, is a critical national issue,” the report states.
The other two deficient bridges in Clinton are the Second and Fourth Street viaducts, which carry train traffic and were not evaluated in the Transportation for America study. Union Pacific’s plans to construct a $400 million clear span bridge to replace the current swing span bridge could mean those viaducts fall to the wayside.
“Second Street and Fourth Street may one day be abandoned once the UP high bridge is built and we can possibly enter South Clinton under the railroad bridge,” Craft said.
In addition to the deficient bridges, the city also maintains some that are obsolete, such as 28th Avenue North, Cleveland Street and 29th Avenue North.
“This will be worked into upcoming budgets as they will be fully city funded,” Craft said.
Clinton County is responsible for 275 bridges with spans of 20 feet or greater and another 55 that have spans shorter than 20 feet.
The conditions of those bridges vary significantly, County Engineer Todd Kinney said.
Ten are designated structurally deficient, with half on the county’s five-year construction program. The bridges on 275th, 230th, 145th, 340th and 200th Avenues will cost the county $950,000 over the next five years.
Bridges also can fall into the “functionally obsolete.” Clinton’s largest bridges carry this designation.
The North bridge and the South bridge, which are maintained by the Iowa Department of Transportation, both have older design features not built to current standards. Specifically, both bridges have decks that are not wide enough, according to Mike Todsen, a special projects engineer with the Iowa DOT’s Office of Bridges and Structures.
The North bridge, which was built in 1974, carries around 7,500 vehicles a day across Iowa and Illinois 136. Nearly 11,000 vehicles cross the Mississippi River on U.S. 30 on the South bridge, built in 1956, daily.
Large state-maintained structures such as this will last anywhere from 75 to 100 years, Todsen said, making these bridges only middle-aged compared to the rest of the state’s aging infrastructure.
Iowa would need to spend five to 10 years and more than $50 million to replace each of the bridges in Clinton, Todsen estimated. Because they are both structurally safe and sound, they aren’t in the state’s five-year plan for replacement.
Built in 1932, the Savanna-Sabula bridge is labelled structurally deficient, but also is functionally obsolete. The Illinois Department of Transportation is leading the design work for that bridge replacement. The structure, which carries U.S. 52 across the Mississippi River, will likely be replaced by 2016.
“There are a lot of bridges in the state competing for the same funds. With the cost to replace the 30 and 136 bridges, the condition of these bridges would have to deteriorate more,” Todsen said. “Being that these bridges, though they are narrow, are in good shape, they are not on the top of the list to be replaced.”