CHICAGO (CBS) — A blunt warning tonight to the City of Chicago: Replace the crumbling bridges.

CBS 2 first reported on the Lake Shore Drive overpass over Grand Avenue after a viewer wrote to us saying concrete chunks hit his car.

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In this original report, Chris Martinez returns to the site with a structural engineer.

From the view of an expert’s eyes, it’s not a pretty sight.

“As we stand here, something can fall on us,” said Engineering Professor GK Fu

Professor Fu literally wrote the book on bridge design and just by looking, he spotted rusting and cracks beneath the Lake Shore Drive overpass where he says concrete is set to crumble.

“Certainly it’s a hazard to safety. It should never happen,” said Professor Fu.

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But we saw last week how easily it can happen.

Several chunks of falling concrete from the bridge crushed the hood of Bill Cantrell’s car.

“It sounded like a bomb going off in the car,” said Cantrell.

And turns out, he’s not the first. Another driver faced damage last summer at nearly the exact same spot.

After CBS 2 reported the problem city crews inspected the span finding several brittle sections easily chipped away.

But that’s just a small fraction of what Professor Fu says needs to come down.

“It should be replaced,” said Professor Fu. “The whole deck should be replaced.”

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Professor Fu says even with that crumbling exterior he believes the bridge itself is stable but he says the city needs to consider using nets or plywood to keep that concrete from falling to the road and sidewalk.