Sound Transit shuttle buses replaced light-rail service in downtown Seattle on Tuesday between the Westlake and Stadium stations after a mechanical issue, according to the transit agency.  

Failure of emergency ventilation fans early Thursday at the Pioneer Square Station caused the closure, the agency said. 

There was no estimated time for regular service to be restored as of Tuesday evening.

Link Shuttle buses are replacing the 1 Line between Westlake Sta and Stadium Sta until further notice. https://t.co/7eQkl6bzO7

At about 3 a.m., transit staff learned of an electrical malfunction related to the ventilation, according to John Gallagher, Sound Transit spokesperson. Seattle City Light personnel were helping to identify and solve the problem, he said.

Twelve hours later, electrical teams were still “running all kinds of tests” but had yet to pinpoint the cause of the failure, Gallagher said.

Trains were running at normal 10-minute frequencies between Westlake and Northgate and between Sodo and Angle Lake.

Sound Transit was having riders at Westlake Station use the southbound platform to go north toward the University of Washington and Northgate Station. The trains were reversing direction there from south to north in a wishbone pattern while other downtown stations weren’t reachable.

The downtown tunnel stations lack crossover switches that would allow trains to go one stop farther south and reach University Street Station. Trains were using a crossover switch between Capitol Hill and Westlake to return to the northbound rails.

Transit staff was helping riders find downtown buses that were substituting for trains downtown, and to reach the reversing trains at Westlake and Sodo Stations, Gallagher said.

The downtown transit tunnel, completed in 1989, contains several ventilation fans intended to remove smoke in case of an emergency. Fire codes require they work properly during passenger service.

Ventilation is one of many tunnel systems Sound Transit must refurbish in the near future, after its board voted late last year to assume control of the nearly 34-year-old tunnel from King County Metro.

Insulation, bearings and other parts need reconditioning, though that could be deferred by a couple years, according to a 2020 safety engineering report. The study also said older fire-alarm wiring and devices needed replacement in one or two years. Sound Transit has plans for deeper engineering in 2023 to pin down the top priorities and schedules to modernize the aging tunnel, especially its behind-the-scenes equipment.

A technical description of Tuesday’s exact problem wasn’t immediately available from Sound Transit.

Passengers had been able to get on and off shuttle buses at:

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