Bellevue and Eastside riders who depend on Sound Transit express buses have four days to plan new commutes.

Six ST Express routes disappear starting Aug. 29, replaced by Link light rail connections and, for the first time, overnight bus service linking Redmond, Bellevue and downtown Seattle.

Routes 550 and 554, the two cross-lake buses most used by Bellevue commuters, end Saturday. Route 515, which serves early-morning riders heading from Lynnwood to downtown Seattle, follows on Monday, Aug. 31. Routes 570, 580 and 586 also go away over the same weekend.

The changes are permanent.

Sound Transit says the 2 Line, which began crossing Lake Washington on the I-90 floating bridge on March 28, now covers the same territory. Trains run roughly 5 a.m. to midnight, every eight minutes at peak and every 10 to 15 minutes off-peak, at a flat $3 adult fare identical to the express bus.

New overnight service fills the gap after midnight

The agency is simultaneously launching Route 547, a Night Bus running between downtown Seattle, Bellevue and Redmond after the last trains each night.

Service begins after the final Link trains Saturday, Aug. 29, with buses arriving approximately every 30 minutes regardless of the day of the week. Sound Transit's Norizumi Cuplin wrote on the agency's blog that a few extra trips run Sundays because Link starts later and stops earlier that day.

A second Night Bus, Route 597, launches Sunday, Aug. 30, connecting Lakewood, Tacoma, Federal Way and downtown Seattle on the same 30-minute frequency. It replaces the daytime coverage previously provided by Route 570, but as an overnight-only service operated by Pierce Transit.

Sound Transit's overnight pilot began in March with a single route between Sea-Tac Airport and downtown Seattle. The agency says that pilot has drawn hundreds of riders each week.

What Bellevue riders should know

Route 554 riders (Issaquah to downtown Seattle via I-90): Switch to the Link 2 Line or the upgraded Route 556, which now runs between Issaquah and Bellevue Transit Center every 15 minutes with longer service hours and new Issaquah stops. The 556 connects to the 2 Line at South Bellevue and Bellevue Downtown stations.

Route 550 riders (Bellevue to downtown Seattle): Board the 2 Line at Bellevue Downtown Station, a short walk from the old Bellevue Transit Center stop at 110th Avenue NE and NE 6th Street. South-end commuters can use South Bellevue Station's park-and-ride garage.

Route 515 early-morning riders: Sound Transit recommends catching Route 512 from Lynnwood City Center at 4:17 a.m. to Mountlake Terrace station, then transferring to Route 510 or the Link 1 Line at Northgate Station.

Full schedule details are available at soundtransit.org/ride-with-us/changes-affect-my-ride/service-changes.

Other changes in the region

Route 513 adds bi-directional service. Route 522 shortens to Shoreline South with 15-minute headways. Route 574 shortens to Federal Way, also at 15-minute frequency. King County Metro is separately adding seven new bus routes and expanded weekend and morning service starting the same day, KING 5 reported.

Sound Transit is also working with Community Transit to extend overnight service to Everett, though no launch date has been set.