BOISE -- Washington State Police say a truck hitting a bridge on Interstate 5 in western Washington led to a collapse, but as the country's infrastructure is aging, many are interested in the bridge construction as well.

The Washington bridge was built in 1955, according to federal data. Overall in Idaho, there are 574 bridges, that like the one in Washington, are over 50 years old, which the Idaho Transportation Department says is the ideal lifespan for a bridge.

Within the next 10 years, more than 1,000 Idaho bridges will be that old, but funding is hard to come by for complete replacements.

Idaho's bridges are inspected at least every two years, and then they're ranked for sufficiency and figured into a maintenance schedule.

The transportation board ultimately decides which bridges are going to be replaced, which ones get what level of maintenance on them. A lot of that is determined by finances, ITD spokesman Reed Hollinshead said.

Federal data shows Idaho's bridges average a sufficiency rating of 84.5 out of 100. For reference, the bridge that collapsed in Washington was rated a 57.4.

Other data shows the I-5 bridge was considered functionally obsolete, meaning its design wasn't currently adequate for traffic demands for some reason, but not necessarily unsafe.

That could be a bridge that was built recently but now it's handling three times as much traffic as it was built for originally, Hollinshead said.

The Broadway Bridge in Boise is one in Idaho that is classified as functionally obsolete because it wasn't designed to handle the amount of traffic that now flows by Boise State University. So, it's set to be replaced soon.

In Idaho, we looked at bridges with the same design construction as the Washington bridge. It's a steel structure with a through truss design. There are 20 in Idaho, with three considered functionally obsolete and 14 with some type of structural deficiency.

There is only one bridge in the state ITD considers very similar to, though not exactly like, the I-5 bridge. It's to be replaced because of a low sufficiency rating.

Like the I-5 bridge - three are considered functionally obsolete.

It's over in eastern Idaho near St. Anthony on U.S. 20, the business route. It's the Del Rio Bridge. It's due to be replaced in 2014, Hollinshead said.

Again, ITD points out the Washington bridge collapse appears to be because a truck hit it. The department says any bridge hit in the wrong spot by a fast-moving heavy truck could have similar consequences.

Hollinshead says ITD is very thankful no one was killed in Washington's collapse, and they add that travelers in Idaho face no immediate dangers, even with an aging infrastructure.

If [a bridge] was a danger in any way to the public, we would close it down. But what the public can do for us to help us out, is they can be kind of de facto bridge inspectors and when they're driving across these structures and see a problem, just let us know, Hollinshead said.

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