Deal would let light-rail trains use I-90 express lanes

Sound Transit and the state Department of Transportation reached a deal today for light-rail trains to operate in what are now the center express lanes of Interstate 90.

The rail corridor across Lake Washington has been in design for several years. It was approved by voters as part of a 2008 Sound Transit ballot measure that raises sales taxes to fund suburban lines north, east and south of Seattle.

Today, the DOT agreed to let trains occupy the express lanes, in exchange for $153 million that Sound Transit is spending to add carpool lanes and ramps to the main east- and westbound freeway sections. Washington DOT is spending an additional $45 million on the lanes and ramps.

The new carpool lanes will be needed to replace the express lanes, which serve carpools and Mercer Island drivers. Part of the carpool-lane project is already built, westbound from Bellevue to mid-island.

For rail backers, the importance of the tentative deal is that it prevents more delays. Construction can stay on schedule to open a light-rail line to Bellevue 10 years from now.

Work on the bridge is to begin in 2015 — shifting cars and buses from the express lanes into the new carpool lanes.

Sound Transit would lease the express-lane space for 40 years, with an option to renew for 35 more years.

Transit leaders were eager to take the offer because the state says it's out of money to help build the carpool lanes, said Jim Edwards, capital projects director.

By taking on nearly all the construction burden, instead of waiting for the state to put up tens of millions of dollars, Sound Transit protects itself from delays.

Opponents have a lawsuit pending in state court challenging the attempt to convert interstate highway lanes, funded mainly by gas taxes, into a rail corridor.

Sound Transit argues that documents dating back more than three decades show that federal, state and local governments have agreed I-90 would accommodate high-capacity transit.

The new agreement, signed today by Sound Transit CEO Joni Earl and state Transportation Secretary Paula Hammond, is subject to approval by the full transit board in the next few weeks.

This would be the world's first rail line on a floating bridge — a plan that requires engineers to design unique rail joints so that trains can move between the fixed and floating bridge sections without going off track. In addition, some concrete will need to be removed from the bridge and replaced with lighter paving materials to improve its buoyancy.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com