MOVILLE, Iowa | A huge map covered with colored dots hangs on the wall above Woodbury County Engineer Mark Nahra's desk.
He points out the colors and their meaning: blue or green mark county bridges that are in good shape. Red or yellow means those bridges need to be repaired or replaced.
Nahra's map has too many red and yellow dots for his liking. And, if other county engineers in Iowa had similar maps, most of them would be seeing red and yellow, too.
Rising construction costs, stagnant funding streams and a large generation of bridges reaching the end of their life span have led to a backlog of bridges in need of replacement across Iowa, and county engineers face tough choices about how to keep up with the ever-growing list of old bridges and maintain public safety.
"We have more demand on roads than we ever have in the past, and we're not getting things replaced to meet that demand," Nahra said. "If we don't speed up our replacement process, I see we're going to have to close some of our roads, at least temporarily."
Woodbury County has already closed some roads, and Nahra said his office lowers posted weight limits on 10-20 bridges a year. But closing roads doesn't work everywhere, he said, and reducing weight limits doesn't always detour heavy trucks and farm equipment.
"I have bridges that do worry me and that's because people tend to ignore the postings. Someday, someone's luck is going to run out, and that's what worries me," Nahra said.
Sioux County Engineer Doug Julius said his department is currently holding its own, spending $1.25 million to repair and replace as many of its 390 bridges each year as possible, but eventually, some roads may have to be considered for closure. With 16-20 bridges in the five-year construction plan and the same number waiting to get in, it's unlikely they'll all get fixed or replaced before they're too old.
"If you had to fix all those today, there wouldn't be enough money to do it," Julius said.
Woodbury County has 317 bridges longer than 20 feet and more than 400 bridges, culverts and other drainage structures under 20 feet. Average life expectancy for bridges is 50 years, and the county's bridges currently average about 41 years old. There are 69 bridges determined to have five or fewer years of life left. Nahra's $1.5 million annual bridge repair/replacement budget will enable him to address 32 of them in the next five years.
"We're trying to get rid of the ones that are the most seriously deficient," he said. "With the way costs have been going, sometimes the five-year program stretches into six years."
Nahra said construction costs have tripled in the 29 years since he graduated from college, and funding sources haven't kept up. Iowa's county engineers have lobbied for an increase of the state's gas tax, which helps fund road and bridge repairs, but to no avail. Federal funding can be inconsistent.
In an effort to catch up, the Woodbury County Board is considering a significant increase in the Rural Basic Fund property tax levy to raise an additional $1.3 million in each of the next five years, enabing Nahra to fix or repair an additional 14 bridges. The board has yet to vote on the levy increase.
Woodbury County's rural levy increase discussions have attracted interest.
"That would be a big help if you could throw an extra million a year at bridges," said Plymouth County Engineer Tom Rohe. "We'd like to be able to do more. We're probably not keeping up at this point."
Of Plymouth County's 460 bridges, 50 are in the five-year construction plan, and another 50 probably could be, Rohe said. He spends $1 million-$2 million to replace eight to 10 bridges each year.
However, he said, Plymouth County does not have enough spare room under its rural levy cap to generate enough extra funding to make a difference.
Sioux County does, Julius said, but raising that levy has not been suggested. Julius said he didn't know how much support such a plan would have.
"You can only get so much money" from taxpayers, he said.
Engineers said their backlog isn't likely to go down anytime soon. Farm equipment is getting bigger all the time, increasing the weight bridges bear. A bridge-building boom from the 1930s through the '60s, when counties across the state upgraded rural roads, created a large bubble in the number of bridges at the end of their life span.
Some headway has been made. Woodbury County has reduced the number of bridges with inspection ratings of 25 or lower from 43 to 29 in the past five years. Engineers replace smaller bridges with culverts when possible, a cheaper alternative that can enable counties to upgrade more bridges each year.
New bridges are built to last 75 years, Nahra said. Timber pilings are rarely used nowadays, and the use of epoxy-coated steel helps prevent rust. Nahra foresees a time, maybe 10 years from now, when the average age of Woodbury County's bridges dips below 30 years.
"We've made some progress," he said.
But there's a long road ahead to catch up with the growing list of aging bridges.
"I think all counties are in that situation," Rohe said. "Whether we can catch up, I don't know."