Traffic Lab is a Seattle Times project that digs into the region’s transportation issues to explore the policies and politics that determine how we get around and how billions of dollars in public money are spent.

Sound Transit will close five downtown stations all weekend, while contractors continue to link the Seattle light rail mainline to a future track segment serving the Eastside.

Westlake, Symphony, Pioneer Square, International District/Chinatown and Stadium light rail stops will shut down at 10 p.m. Friday and reopen around 5 a.m. Monday.

Shuttle buses will operate every 10 to 15 minutes and pick up riders at Capitol Hill Station, the five closed stations and Sodo Station. Trains will run between Lynnwood and Capitol Hill, and between Sodo and Angle Lake including SeaTac/Airport Station. Besides the shuttles, many regular bus lines can help people detour, notably Route 101 from Renton, Route 150 from Kent and Route 594 from Tacoma, all stopping in both Sodo and downtown.

Two more weekend closures are expected sometime in January and one in February, as Sound Transit aims to open light rail across Lake Washington to Bellevue by late 2025, in the former express lanes of the Interstate 90 floating bridge, along with stations at Mercer Island and Judkins Park. Low-speed train tests just began on the island.

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Saturdays are a popular day for light rail, with an average 82,000 riders on the 1 Line between Lynnwood and Angle Lake as of September — higher than the 79,000 weekday average.

Construction this weekend won’t interfere with stadium events as the Huskies are at Penn State, the Seahawks have a bye and Sounders FC don’t have a match until the Nov. 23-24 weekend. Sound Transit suggests Kraken hockey fans Friday night take Route 8 up Denny Way to catch trains northbound at Capitol Hill Station, rather than the usual trip involving Seattle Center Monorail and Westlake Station.

Contractors this weekend will replace a 1 Line signal cabinet near International District/Chinatown Station with a new version that adds 2 Line signals, said spokesperson John Gallagher. Among other functions, it will control a switching complex, where 2 Line tracks arriving from I-90 meet the 1 Line tracks going north-south.

Though the job has been on the drawing board for months, the closure will aggravate rider frustrations over service interruptions, caused mainly by power loss and sudden train stalls. So far in November, light rail trains have been delayed at least six times, or had to alternate for up to an hour on a single track. On Oct. 19, for nearly the whole day, service in North Seattle was slowed to 30 minutes between trains.