Light-rail train service in North Seattle was fully restored just before 5 p.m. Thursday after malfunctioning fire safety equipment caused a six-hour closure of U District, Roosevelt and Northgate stations, according to Sound Transit.

Passengers at University of Washington Station, next to Husky Stadium, were diverted off the trains to shuttle buses, which also gathered riders curbside next to the three blocked stations.

Trains rolled empty in the tunnel from UW to Northgate, then turned back south, so the remaining 20 miles of Sound Transit’s 1 Line could continue normally, with trains arriving every 10 minutes or sooner from Angle Lake and SeaTac.

Sound Transit initially sent alerts about a “mechanical issue.” Some transit riders complained on Twitter about the lack of explanation after the shutdowns at 10:40 a.m. Officials sent email service updates at 11:40 a.m. and 12:10 p.m. with shuttle bus instructions. Spokesperson John Gallagher cautioned riders to expect “some residual delays” early Thursday evening as train stops reopen.

The agency’s CEO, Peter Rogoff, promised last winter to improve customer notifications, after the Apple Cup stall on Nov. 26, when confused riders walked out of stuck railcars near the UW Station. Officials made similar pledges in 2010 after a rogue fire alarm forced a sudden closure of the downtown transit tunnel.

A new communications plan hasn’t yet been produced and vetted by elected officials on the transit board. The 18-member board is led by Chair Kent Keel, a University Place councilmember and vice chairs King County Executive Dow Constantine and Snohomish County Executive Dave Somers.

By early afternoon, Sound Transit apologized for the inconvenience and sent some staff to guide passengers, some of whom tweeted about long waits or not enough shuttle buses.

U District Station is the busiest on the 24-mile corridor, fueled by the return of students to campus last fall. An average 56,000 daily riders traveled on light rail as of January, as buses and trains rebound from losses during the pandemic.