Sound Transit is expected to take a big step Thursday toward supporting a light-rail tunnel through downtown Bellevue.

Sound Transit is expected to take a big step Thursday toward supporting a light-rail tunnel through downtown Bellevue.

The final decision remains a year off, but transit-board leaders are ready to approve a tunnel as one of two options for engineering and environmental studies over the next year. If the city and transit officials fail to agree on a final tunnel plan, a surface route would be built instead.

While putting the tracks underground would reduce train collisions and prevent traffic snarls, it could add $320 million in cost and delay opening by a year, to 2021.

Unlimited Digital Access. $1 for 4 weeks.

The Bellevue City Council unanimously supports a tunnel, and on Monday night voted 4-3 to endorse a general strategy to help Sound Transit pay for it. Bellevue would contribute $150 million worth of rights of way, utility relocation, street reconstruction or tax revenue.

“This keeps the possibility of a tunnel alive. We still have the ability, through the rest of the year, to make the tunnel more affordable,” said Bellevue Councilwoman Claudia Balducci, also a transit-board member.

Sound Transit would seek $75 million in cost cuts. They include choosing a straighter route on Bellevue Way and 112th Avenue Southeast, just south of downtown, instead of costlier paths that wind through or around Mercer Slough close to Interstate 405.

The remaining $95 million would come from schedule tweaks or federal grants. The one-year delay is supposed to make debt financing easier and loosen the project’s cash flow by postponing the operating costs.

Tunnel backers are undaunted by the recession, which is forecast to reduce Sound Transit’s long-term income by $3 billion over the course of the 15-year, 34-mile expansion plan voters passed in 2008. At that time, estimates were based on generic costs of elevated trackway, leaving the alignment decision for later.

Board members are open-minded about a tunnel, but some feel Bellevue is relying too much on Sound Transit to cover funding shortages, Chairman Aaron Reardon, the Snohomish County executive, said. The agency already erased some cushion from its financial plan. “Let’s not get ourselves in a position where scope is compromised,” he said.

In other words, uncontrolled tunnel costs could reduce the flow of cash needed to finish other track segments. That sort of crisis might force Sound Transit to delay or reduce projects, or prolong the bonds and taxes.

City and downtown business leaders have resisted a surface route, largely because trains would add congestion to the east-west streets into downtown.

Meanwhile, Bellevue has watched Sound Transit design Seattle tunnels through Beacon Hill, Capitol Hill and, eventually, under the University District to the Roosevelt neighborhood.

Balducci guesses the transit board — comprising local elected officials in three counties — would be voting Thursday to pick a surface route instead of a Bellevue tunnel, if not for Monday’s narrow 4-3 City Council vote to offer $150 million, in a “term sheet” agreement with Sound Transit. She feared it would fail, but Mayor Don Davidson changed his mind to vote yes.

“I was surprised,” Balducci said.

Sound Transit now will spend about $1.5 million to advance the tunnel to about 15 percent design, she said.

Also voting yes were council members Grant Degginger and John Chelminiak; against were Conrad Lee, Jennifer Robertson and Kevin Wallace.

Lee said the city was giving away too much too early, for a project he said could hurt the “social fabric” of neighborhoods.

He discounts the idea Bellevue could wriggle out from under the momentum of the term sheet, which is nonbinding, even if city leaders dislike the design. “Sound Transit is a big, smart political machine. It’s not easy, not at all. We’re playing with a 1,600-pound gorilla,” Lee said.

Bellevue neighbors are taking note of noise problems on Sound Transit’s first line through South Seattle and Tukwila, and fear the same at home. The agency is retrofitting parts of the line now, and Balducci said there are years to learn about taming noise problems before the Bellevue startup.

Joseph Rosmann, a Surrey Downs neighborhood advocate, said the recession will cause pressure to build on the cheap. To him, the latest trade-off, bringing trains to 112th Avenue Southeast, is the first time Sound Transit has chosen an alignment based on financial need rather than spend millions more to satisfy a neighborhood. Maybe the line should end at downtown instead of Overlake, so Sound Transit can afford to do right by its neighbors, he said.

Thousands of taxpayers, tantalized by regional rail maps since the early 1990s, may not be as patient.

Mike Lindblom: 206-515-5631 or