COEUR d'ALENE - Scattered across Idaho's 44 counties, more than 4,000 highway bridges carry motorists from one destination to another.

According to a recent report from Transportation For America, 9 percent of those bridges are considered "structurally deficient" by federal standards.

"Out of 50 states and the District of Columbia, Idaho ranks 33rd nationally in terms of the overall condition of the state's bridges (1 being the worst, 51 being the best)," the report said.

Ten of the 136 bridges in Kootenai County - 7.4 percent - are rated as structurally deficient, the report added. Nearly 1.5 million vehicles pass over Kootenai County bridges every day.

"All of our bridges are safe, and they are regularly maintained, and they're inspected at least every two years," said Barbara Babic, spokeswoman for the Idaho Transportation Department. "Something would be done if (a bridge) were deemed to be unsafe. With that said, Idaho's bridges are aging."

Statistically, the poorest bridges in the state belong to Lincoln County, where 27.7 percent (13 out of 47) are deemed structurally deficient.

Inspectors look over three components of a highway bridge: its superstructure, substructure and deck. A bridge is classified as "structurally deficient" when one component is rated 4 or less on a scale of zero to 9, according to the report.

The low rating indicates a "major defect in (the) support structure or deck," the report said. A deficient bridge requires "significant maintenance, rehabilitation or replacement."

In the Coeur d'Alene/Post Falls corridor, Transportation for America red-flagged two bridges as structurally deficient. One is on South McAvoy Road, a minor span across Cougar Creek.

The second is on U.S. Highway 95, where the well-traveled highway crosses Interstate 90 in Coeur d'Alene. Built in 1960, the bridge sees 30,000 vehicles per day, the report said.

Most highway bridges were designed to last 40-60 years, Babic said, but "they're gonna have to go about 120 years."

Regular maintenance increases the lifespan of a bridge, she added.

The U.S. Highway 95 structure was last inspected on April 17, 2010, and the deck was rebuilt in 2009, according to ITD personnel.

"The safety of the drivers is our top priority," said ITD Public Information Specialist Reed Hollinshead. "We know how long (bridges) have been in service, what kind of traffic they've been getting. It's a small percentage of our bridges that are deficient."

To repair a worn-out span, crews often roll out new asphalt or concrete. The extra layering prevents rebar and other materials from corrosion, Hollinshead said.

Some bridges require more extensive work, such as repairing or reinforcing the foundation. Modern technology has revealed problems unknown to road-builders of earlier generations - for instance, bridges can now be modified to guard against seismic activity, Hollinshead said.

But bridgework is costly.

"The problem we run into is you just don't have the money for those fixes," he added.

With limited resources and a tight budget, ITD cannot rebuild or replace all of the aging bridges throughout the state, Hollinshead explained. The department can, however, inspect the bridges and perform smaller-scale maintenance or repair jobs.

If an old bridge were to become dangerous for travelers, he said, ITD would immediately fix the structure or shut down the road.

Local highway districts maintain and monitor bridges on smaller secondary roads. According to Lynn Humphreys, chairman of the Post Falls Highway District Board, the districts will pull out an old bridge when necessary.

Two years ago, Humphreys said, a bridge on Seltice Way near Riverstone, built in the 1930s, was replaced.

"Each and every bridge is scrutinized, and then they're rated for what condition they're in," he said. "We don't have any bridges that are currently deficient in Post Falls. Most of the bridges that are in Kootenai County are certainly in good repair."

Transportation For America (T4 America) is a diverse coalition working for transportation reform in the United States. Its executive committee includes the American Public Health Association, the National Association of Realtors, the Rails-to-Trails Conservancy and the Natural Resources Defense Council.

"They're a diverse group of organizations that are part of (T4 America)," Babic said. "It's multi-modal, if you will. They're obviously looking at all highway users and their needs."

T4 America collected data from the Department of Transportation and the Federal Highway Administration while piecing together its bridge report.