DETROIT (AP) -- An average of 1,000 vehicles an hour cross the Davison bridge in Detroit to get on Interstate 75. The lanes are tight. Concrete barriers show marks from collisions. But the pavement is smooth.
Nonetheless, the concrete urban bridge is among at least 28 in Michigan labeled "structurally deficient" and "fracture critical." What drivers probably don't see, according to state inspectors, is a deteriorating deck underneath. And while the bridge's steel-capped piers below are in good shape, there's nothing else to support the span if problems developed there.
Should drivers be alarmed? No, officials say. They say bridges in that category simply need regular maintenance and inspection while a long-term plan is developed to rehab them.
"We get up real close and personal," said David Juntunen, bridge operations engineer at the Michigan Department of Transportation. "If there's any question at all, it's closed to traffic."
The Associated Press analyzed data on 607,380 bridges in the National Bridge Inventory, which are subject to national inspection standards. There are 65,605 structurally deficient bridges and 20,808 fracture critical bridges, according to the most recent data. Nearly 7,800 bridges fall into both categories.
Michigan's share of that total is very low. Many are in remote areas where daily use is sporadic.
Most are the responsibility of local governments; only five of the 28 bridges that are structurally deficient and fracture critical are MDOT-owned bridges, although that doesn't make inspections any less stringent.
Besides the Davison bridge, some other high-traffic spans are the bridge over the east channel of the Saginaw River in Bay City and the M-20/Tittabawassee River bridge in Midland. No major construction has been scheduled on the Bay City bridge, but the Midland bridge could be rebuilt in 2018, MDOT said. Most money comes from the federal government.
A bridge is structurally deficient if at least one major component has significant deterioration. A bridge is fracture critical if the failure of a single, vital component could cause a collapse.
"Those terms are engineering terms," Juntunen said.
Bridge experts "realize they're not warm-and-fuzzy phrases," he said. "The best thing we can do is educate the public on what those terms really mean. If a bridge is fracture critical, we have to inspect them more often — but it definitely doesn't mean the bridge is unsafe."
The list of Michigan bridges in both categories has some that don't see much traffic. Three are over the Whitefish River in Alger County in the Upper Peninsula. They are steel truss bridges, with a surface made from timbers, and probably need to be replaced.
"I applied for federal bridge funds for five consecutive years. Each year I'm denied," said Bob Lindbeck, engineer and manager of the Alger County Road Commission.
He said the condition of the bridges forces him to post weight restrictions. That discourages people from living in the area year-round because snow trucks and emergency vehicles can't cross.
"I've got letters of support in my application," Lindbeck said. "People here are very patient but very persistent."
Michigan's main transportation fund is at its lowest level in 30 years when adjusted for inflation because people are driving less and with more fuel-efficient cars. The 19-cents-per-gallon gasoline tax is the same as it was 15 years ago.
In February, Gov. Rick Snyder called for raising fuel taxes and vehicle registration fees by $1.2 billion. But the plan was not embraced in the Legislature, and talks on an alternative have gained little traction.
MDOT spokesman Jeff Cranson said the money would be spread among programs but bridges would benefit.
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