" Falling concrete slabs crushed a car inside one of the city's troubled Big Dig tunnels, killing a woman and tying up traffic Tuesday with another shutdown in the massive building project that has become a central route through the city. The ceiling panels fell because a steel tieback, holding a 40-foot section of the ceiling in place, gave way, Amorello said.  "There was a snapping sound heard," Amorello said. "One of the tile panels from the roof released. It caused a series of panels to be released."  The ceiling panels were erected there in 1999 and the tiebacks were bolted to the tunnel roof overhead. Other parts of the system were the tiebacks are believed to have been used were being inspected."

I didn't realize we were anchoring big (looks like 10x20) concrete panels to the undersides of ceilings in high volume thoroughfares.  Is something wrong with this picture? 

Christopher