FRANKLIN, Tenn. -- The Tennessee Department of Transportation said on Tuesday they will examine close to 600 signs across the state that are similar to the one that fell on Interstate 65 on Monday morning.

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The sign that fell and others like it are called cantilever signs, which are supported by only one pole on one side.

The signs should stand for 50 years on average, but the one that fell in Franklin only stood for 15 years, according to TDOT.

"What we saw yesterday shouldn't have happened," said TDOT Chief Engineer Paul Degges.

The sign's bolts didn't pop out and the foundation didn't crack. It appeared that the metal simply split apart at the pole's base, but how did that happen?

"We really don't know right now. That's what I've asked our structures divisions to do an analysis of," said Degges.

The department said they think prolonged exposure to wind created by tractor-trailers may have contributed to the problem.

TDOT said the signs don't have to be inspected, but they periodically do this as part of their general work. They said there was no problem with the sign when they last inspected it in 2000.

"Are you confident in the safety of the signs on the road right now?" the I-Team's Jeremy Finley asked Degges.

"Yes I am. We are doing more than most people are doing across the nation," he said.

The TDOT has added extra bolts at the base of nearly half of all the cantilever signs across the state. Workers will now go out to determine if more needs to be done.

"Anytime where we have a failure like this, I think it's important for the department to go out (and) look at the other structures across the state," said Degges.

TDOT was also closely analyzing the split pipe that caused the sign to fall.

The sign fell on the southbound lanes about 11:30 a.m. near the Cool Springs Boulevard exit that leads to Cool Springs Mall.

"This is very dangerous for the motoring public, and we are very thankful there was nobody traveling underneath the sign at the time that it fell," said TDOT spokeswoman B.J. Doughty.

There had been no complaint on record about the sign from a driver, and it had never been hit as part of a traffic crash.

The federal government doesn't require states to inspect highway signs, but TDOT did inspect all signs across the state in 2000, a representative said.

The I-Team reported that problems with the cantilever signs have caused structures to fall into traffic before.

A federal highway administration report cited a 2002 survey of sign inspections in which 54 percent of state transportation agencies reported problems with weld defects in sign and pole construction and cracking.

The sign did not hit any vehicles when it fell, but there was a crash in the area when a car rear-ended two other vehicles.

Two adults and two children were taken to a local hospital but suffered only minor injuries, officials said.

"Very easily could someone, had they driven under that sign, what was happening, or somebody was just not paying attention, talking on the cell phone or something like that, that would fallen onto a car, would’ve easily cut a car in half and the people inside of it," said Tara Vonch.

Vonch and her mother-in-law were running errands when the sign fell.

The sign was cleared up and all of the lanes of traffic were open for the evening rush hour on Monday.

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