Boston Tunnel Design Faulted in Collapse

Federal inspectors have found that a Big Dig tunnel ceiling that collapsed in July and killed a motorist was designed with a smaller margin of safety than other tunnel ceilings in America, according to a report obtained by the Boston Globe.

The Interstate 90 connector tunnel's drop ceiling panels were held in place by steel hangers suspended from bolts that were glued into the tunnel ceiling with epoxy. But there were no beams attaching the ceiling to the walls, and there were half as many bolts used as called for in the original design.

No redundancy was built into the ceiling in the event the hangers failed, according to a preliminary report by the National Transportation Safety Board obtained by the Globe.