The state's planned Highway 99 tunnel might not be finished until November 2016, a year later than the Department of Transportation earlier planned.
Transportation managers said Thursday morning they've added 360 days to the schedule to take pressure off the tunnel's three prospective construction teams -- who said in closed-door talks that they were squeamish about an aggressive DOT timeline.
But if a team can guarantee an quicker finish in 2015, that would give them a slight advantage in bidding competition, for a job that's in the vicinity of $1.09 billion.
For drivers, a slower timeline means they would use the old Alaskan Way Viaduct a year longer. The viaduct would continue to be examined quarterly and reinforced if needed.
The design calls for a hole 56 feet wide beneath downtown. That will require the world's largest-ever tunnel boring machine, said segment manager Linea Laird.
A new machine, worth about $80 million, will take three to six months longer to build than the 18 months DOT expected.
And the state is slowing the pace of drilling to allow for more deliberate soil-removal and machine maintenance. Without careful attention of both the soil and the surface, creating a tunnel can cause ground settlement that threatens utilities or even building foundations.
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