LYNNWOOD — Partial light rail service between Bellevue and Redmond will get more evaluation after the Sound Transit board approved spending $6 million toward it Thursday.

But Snohomish County leaders on the board said the East Link “starter line” shouldn’t come at the expense of the timeline for light rail service in Lynnwood, Mountlake Terrace and Shoreline.

“We’ve been waiting,” Lynnwood Mayor Christine Frizzellsaid. “I get questions every week about how much longer we have to wait … Snohomish County wants to ride, too.”

Frizzell was the only no vote on the board, which supported the resolution 16-1.

Construction quality issues, costs and delays pushed out the timelines for light rail projects along the I-405 corridor as well as north into Snohomish County. But the sequence of which comes first affects those after, Sound Transit staff said.

If Lynnwood opens first next year, as construction currently puts it on pace to do by mid-2024, its peak service frequency would be 8 minutes or longer. During busy commute times, that could mean crammed train cars. Its frequency would improve to nearly every 4 minutes with access to the operations and maintenance facility in Bellevue (OMF East).

Without access to OMF East, there won’t be room to store and maintain additional trains, Sound Transit deputy CEO Kimberly Farley said. The only operations site available to the Lynnwood extension would be the OMF Central in the SoDo area of Seattle.

The entire system won’t be connected until deficient concrete construction is fixed along I-90.

But a starter line between Bellevue and Redmond, with 10-minute frequency, could open because it already connects to OMF East. Initially it wouldn’t reach across Lake Washington to Seattle and beyond.

Staff expect to have a more accurate timeline of each light rail expansion project’s opening timeline later this year, Farley said. They’re confident it takes six months between openings, with four months of safety testing and training, plus 2 months to “dial in” service and address passenger feedback when “unexpected things happen,” Farley said.

Sound Transit leaders are working to eliminate further delays to the Lynnwood opening date, she said.

It could mitigate “ripple effects” such as Community Transit’s plans to end bus service into Seattle, Snohomish County Executive Dave Somers said.

Pierce County Executive Bruce Dammeier said Sound Transit’s light rail development focus should be on the “spine” along I-5.

“For me to continue beyond this vote, it is going to be very important to me that the East Link starter line doesn’t delay the opening of Lynnwood,” he said.

At this point, staff are confident an East Link starter line wouldn’t further push out Lynnwood’s opening date, Sound Transit CEO Julie Timm said.

Sound Transit staff plan to make a recommendation to the board this fall about whether or not to authorize the East Link starter line, which, if approved, could begin service early next year.

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This story has been modified to correct the title for Bruce Dammeier, who is the Pierce County Executive.