Tunnel timeline

The National Transportation Safety Board today releases its investigation into a 2006 fatal accident in the Big Dig tunnel connecting the Massachusetts Turnpike to Logan Airport.

Jan. 17, 2003 The Turnpike Authority says the $6.5 billion tunnel has been inspected before opening. The ceiling panels, designed by Gannet Flemming in 1998 and built by Modern Continental, are not part of the inspection.

July 10, 2006 Milena Del Valle and her husband are driving in the eastbound lane of the tunnel to Logan Airport when 20 bolts come loose, releasing 10 ceiling panels. Several of the 4,500-pound panels fall onto the car, killing Del Valle.

July 14 Investigators focus on a possible cause of the collapse: the failure of the epoxy used to fasten the suspended ceiling to the tunnel roof. In 2000, Bechtel/Parsons Brinckerhoff, the company overseeing the Big Dig, had warned Modern Continental that its standard for testing bolts was not tough enough. Modern Continental countered that retesting would be expensive and time-consuming.

July 18 State inspectors conclude that 1,146 hangers suspended from the connector tunnel roof by bolts and epoxy are unreliable. A second support bolt is ordered to be installed beside each suspect one.

Sept. 1 The state reopens a single lane of traffic in the eastbound tunnel.

Dec 23 Westbound lanes open.

June 2 After $54 million in repairs, the final section of the repaired tunnel opens.

SOURCE: Globe Archives

Kathleen Hennrikus/Globe Staff