BOSTON -- From cost overruns to leaky tunnel walls, the Big Dig has had its share of troubles. The latest came Tuesday, when gravel and dirt fell from the tunnel ceiling, hitting several vehicles.

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Gail Huff Reports On Big Dig

NewsCenter 5's Gail Huff reported that federal highway officials reported Monday that the tunnels are safe, but the latest problems are being blamed on construction that's taking place on the roadway surface. Several motorists were showered with dirt and rocks as they drove through the tunnel Tuesday morning. Two lanes inside the tunnel were temporarily shut down.

"It sounded like a gunshot as it hit my windshield. I didn't have time to react to it, so I had to drive through it," said Walter Trider, who said his car is still pockmarked by the gravel and rocks that dropped from the ceiling of the Interstate 93 tunnel near the Purchase Street exit. The debris fell from an overhead air shaft in the rehabbed Dewey Square tunnel, Turnpike Authority officials said.

Timothy Mahoney was headed for the Cape in his Chevy Blazer when he also ran into the shower of rocks and dirt.

"I didn't see anything but I heard the crash, the windshield splintered," Mahoney said.

Big Dig officials said construction on the surface near the tunnel sent debris down an airshaft and contractor Modern Continental assured drivers that it was "an isolated incident and in is in no way related to the structural integrity of the tunnel."

That wasn't a huge reassurance to some nervous drivers.

"I had to drive back home through it tonight and it's just unnerving," Trider said.

One of the vehicles damaged by the dirt was an ambulance. The ambulance company said its vehicles won't be going through the tunnels until it's certain they're safe. In the meantime, Modern Continental said it would cover the cost of damages to the four cars and ambulance that were hit with the debris.