FORT WALTON BEACH — They're exposed to wind and weather from all sides. Many bear thousands of tons of weight daily. Some stand in rushing water 24 hours a day.

Yet almost no one who crosses any of the hundreds of bridges on Northwest Florida roads gives any of that a second thought.

"Bridge maintenance is serious business," said Jason Autrey, public works director for Okaloosa County. "We've got to make sure to stay on top of it."

To ensure that its bridges are maintained — or, when necessary, replaced — Okaloosa and other counties in the state rely on a state-administered federal program that keeps a regular watch on the structures and reports any issues to local officials. The state, which is responsible for maintaining the bridges on state roads and interstate highways, also relies on the program.

In Northwest Florida, the workload is handled by two consulting firms that inspect the dozens of bridges on a two-year cycle.

"They get down to which nuts and bolts are showing rust," said Stephen Furman, public works director in Santa Rosa County. Also, Furman said, divers inspect the pilings of bridges over water. That's particularly important locally, where a number of over-water bridges are "scour-critical" structures — meaning that moving water can wear away the soil around the pilings.

"We all keep an eye on that," said Wilmer Stafford, public works director in Walton County.

The bridge reports, issued quarterly, include terms that, out of context, can seem alarming.

For instance, some bridges are described as "structurally deficient." All that means, though, is that the Florida Department of Transportation "believes a bridge should undergo a series of repairs or replacement within the next six years," according to Ian Satter, the FDOT's district public information director.

Reports also can include the phrase "functionally obsolete." But the phrase "only means that a bridge does not meet current road design standards," according to Satter. It can mean something as simple as a bridge was constructed "at a time when lane widths were narrower than the current standard," Satter noted.

Inspection reports also include a "health index," a combined measure of about a dozen aspects of a bridge's condition. "A low health index (below 85) may ... indicate that it would be more economical to replace the bridge than to repair it," according to Satter.

Reports also include a "sufficiency rating." Satter said that number is used "to help determine whether a bridge that is structurally deficient or functionally obsolete should be repaired or just replaced." Federal authorities use sufficiency rating to determine which bridges are eligible for federal repair or replacement funding.

Bridge replacement is currently a focus of work in Walton, Santa Rosa and Okaloosa counties. All three have a number of older wooded bridges whose pilings and road decking were made with wood treated with creosote, a coal-tar-based preservative. According to the counties' public works directors, the protected wood has, in some cases, begun to deteriorate.

"There's a lot of trouble with rot," Furman said.

Santa Rosa County is working to replace two of its wooded bridges each year with new concrete and steel structures. Typically, the county, which stopped building wood bridges about eight years ago, budgets about $250,000 annually for that work, according to Furman. One reason for the relatively low cost, he said, is that the county has the expertise in-house to do the work and doesn't have to contract with an outside firm.

"We're saving a lot of taxpayer dollars," Furman said. "We're not waiting six months for design work. We're not waiting on a county commission meeting (to approve a construction contract)."

Okaloosa County takes a similar approach. "We try to replace one every year," Autrey said.

Okaloosa's public works personnel can do some of the work in-house. After the structural components of a new concrete and metal bridge are ordered, county crews can install it, Autrey said.

In Walton County, while work can also be done in-house, some projects are done by contractors, according to Stafford.

"The ones on (County Road) 30-A, we'll contract out," he said. The reason, he explained is that contractors can focus their effort solely on 30-A, which is heavily used by tourists heading into and out of Seaside and other beachfront communities.

For Autrey, having an outside evaluation of local bridges is a good thing.

"I personally think it's better to get a third party" to do the inspections, he said. "It's a standard that's widely accepted."