The price of Seattle light-rail project on I-90 bridge goes up

The cost to build light rail on I-90 in Washington between Seattle and Bellevue has zoomed $225 million higher than Sound Transit once estimated, now that final engineering work has revealed the challenge of retrofitting the roadway.

Transit-board members voted unanimously to approve a contract increase Thursday afternoon with construction group Kiewit-Hoffman.

The vote raises the contract amount to $712 million for 7 miles of work, from the International District/Chinatown Station to South Bellevue. It is a crucial phase in creating a $3.7 billion East Link corridor to downtown Bellevue and Overlake, where train service is scheduled to begin in 2023.

The job includes building the world’s only trackway on a floating bridge. The roadway moves with Lake Washington’s water level and must be kept buoyant despite the weight of tracks, ties and trains to be placed in the existing express lanes.

Sound Transit is on the verge of winning final approval by state and federal governments to begin I-90 trackwork this summer, after engineers solved 23 technical issues raised by outside experts.

The $225 million change represents a 46% increase, compared with the $486 million budget for the I-90 trackway construction contract.

The goal is to assure that the floating bridge, which opened in 1989, can resist cracking and meet its 100-year design life span despite thousands of trips by 600,000-lb trains. The contract increase includes a 7% contingency for Kiewit if needed.