INVESTIGATORS believe there could be nearly 280 weak fixings in Boston's Big Dig cross-city tunnel following the death of a female car passenger, who was crushed by 12 tonnes of falling concrete ceiling tiles.
Milena Del Valle was killed by three concrete tiles and inspectors now believe that in two other adjoining sections of the tunnel, as well as traffic ramps, there could be a further 278 weaknesses.
Massachusetts Governor Mitt Romney believes that there are 84 potential trouble spots alone in the tunnel where Mrs Del Valle was killed.
It is not yet known exactly what went wrong but speculation has centred on bolts used to secure the ceiling panels to the roof of the tunnel.
In some cases, inspectors have found bolts pulled as much a centimetre away from the tunnel's concrete roof.
Another ramp used by motorists as a detour around the accident scene has since been closed to traffic because of potential problems with 40 of the bolts that hold up the ceiling panels.
The Big Dig project cost nearly £8 billion to build after a politically charged saga of delays and leaks.
After work began in 1991, workers were confronted with problems including underground water and gas pipes, electricity wires, building foundations and sunken ships.
In 2004, leaks occurred in the tunnel caused by contractors failing to remove gravel and other debris before pouring concrete.