The following report by Team 4 investigator Paul Van Osdol first aired on Channel 4 Action News at 5 p.m. on Dec. 28, 2005.

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The Pennsylvania Department of Transportation knew the Lakeview Drive Bridge had problems -- it was just inspected in August and classified as structurally deficient.

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VIDEO: Watch Team 4 investigator Paul Van Osdol's report -- Team 4: Bridge Safety

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But there are plenty of other bridges just like the one that collapsed on Interstate 70 on Tuesday - - more than 6,000 in Pennsylvania are also structurally deficient.

At its last inspection the bridge scored a four on a scale of one to 10 indicating structural problems but none so severe to cause a collapse.

"The analysis we've done -- the rigorous structural analysis based on the last inspection report -- indicates that this bridge should not have fallen down on its own accord without something else happening to it," said Gary Hoffman, the PennDOT deputy secretary.

Hoffman said the bridge might have been rammed repeatedly by big trucks.

But University of Pittsburgh engineering professor Christopher Earls says he doubts trucks caused the collapse.

"The fact that the trailer hits it could spill some concrete off, but it's likely not to cause a catastrophic failure. And it really shouldn't under any circumstance," said Earls.

Earls believes a more likely cause was years of road salt slowly corroding the steel reinforcing rods holding up the concrete beams. That corrosion would be nearly impossible for PennDOT inspectors to detect.

"There are quite a few bridges unfortunately stricken with this corrosion problem and we just can't know how many there are," said Earls.

PennDOT does know 25 percent of the state's bridges are classified structurally deficient -- just like the bridge that collapsed. Structurally deficient means the bridges have significant deterioration but they should still be safe. Pennsylvania is the third worst state in the country for bad bridges.

Two of the most structurally deficient area bridges are the 31st Street Bridge and the Boulevard of the Allies Bridge crossing Forbes. Both of them are scheduled for repairs next year, but PennDOT says it could take two decades to fix all the state's bad bridges.

Gov. Ed Rendell told Channel 4 Action News the state needs more federal money to do the job faster.

"Even a gas tax increase would shorten that time span but would not shorten it enough to ensure public safety. So this is something I think the entire nation has to take a look and and we have to take a real serious look at," said Rendell.

There has been a lot of mine subsidence near the bridge on Interstate 70 that collapsed Tuesday, but PennDOT and the Pitt professor say that probably did not cause the collapse.

Team 4 asked PennDOT for copies of the two recent inspection reports on the Washington County bridge. They refused to make the reports public, saying they are not a public record under state law.