Predecessors on
Sound Transit Express route 532 at
Bellevue Transit Center The
Interstate 405 (I-405) and
State Route 522 (SR522) corridors are served by
Sound Transit Express bus routes that were launched in the late 1990s and early 2000s by
Sound Transit to provide service between regional hubs. They replaced earlier
King County Metro (formerly Metro Transit) bus routes from as early as the 1970s to provide inter-suburban service and bypass
Downtown Seattle, the hub of the regional transit network. The first of these was Route 240, an all-day suburban route which launched in 1973 and served a corridor from
Burien to
Bothell with intermediate stops at
Seattle–Tacoma International Airport,
Southcenter Mall, and
Bellevue. An express variant, Route 340, connected several
park-and-ride lots on I-405 and
SR518 between Burien and
Shoreline; it was the longest route in the Metro system, taking three hours on a round trip. The south half of I-405 is served by Route 560, which travels from the
Westwood Village shopping center in
West Seattle to
Burien,
Seattle–Tacoma International Airport,
Renton, and
Bellevue. It was launched by Sound Transit in September 2000 and originally continued north to
West Seattle Junction until the route was cut in 2013. The north half of I-405, from
Bellevue to
Lynnwood, is served by Route 535; the route has stops in northern
Kirkland and at the
University of Washington Bothell campus. The corridor is also served by Route 532, which continues to
Everett. Both routes were part of the original Sound Transit Express launch in September 1999; route 535 has all-day service on weekdays and Saturdays, while route 532 is peak-only. Route 522 originally continued into Downtown Seattle until it was truncated to coincide with the opening of
Roosevelt station in 2021.
BRT proposals and studies I-405 was originally built as a
bypass around Seattle, but had become heavily congested during peak hours after the development of Eastside cities in the late 20th century. A set of
high-occupancy vehicle lanes (HOV lanes) were constructed along its entire length from 1983 to 2002 to address congestion issues and encourage the use of
carpools and public transit. The Regional Transit Authority (now Sound Transit) planned to construct direct-access ramps for the HOV lanes to improve bus service on the corridor, as the existing network of
flyer stops required buses to weave in and out of the other lanes. The ramps were funded by the
Sound Move ballot measure, which was approved by voters in 1996, and intended to be a precursor to a
bus rapid transit (BRT) system. The conversion of the HOV lanes on I-405 for transit-only use or the construction of an adjacent facility was proposed as early as 1990 by Metro Transit (now King County Metro). A
commuter rail or
light rail line using the existing
Eastside Rail Corridor, a former freight line that runs parallel to I-405, was also considered in various plans. The state government convened a 19-member committee in 2001 to draft a long-range plan for the I-405 corridor that would be used to recommend projects in future legislative funding packages. Sound Transit, a stakeholder in the committee, solicited ideas for a bus rapid transit system with grade-separated busways. The state committee endorsed the addition of managed
high-occupancy toll lanes (HOT lanes) lanes that would also be used by a bus rapid transit system with park-and-ride stops spaced apart. A statewide
referendum to fund transportation projects, including the first phases of the I-405 expansion and improvements, was rejected by Washington voters in 2002. The BRT project was bundled into the unfunded phase of the corridor's master plan, which would take an estimated 20 years to construct with additional funding sources. Sound Transit updated their long-range plan in 2005 to add several BRT corridors, including I-405 from Renton to Bothell, and a high-capacity transit option on SR522 that would be either rail or bus-based rapid transit. Funding to plan and design the I-405 BRT line was included by Sound Transit in their portion of the 2007
Roads and Transit package, which was defeated by voters in the Seattle area. The I-405 planning study was retained in the separate
Sound Transit 2 ballot measure, which was approved by voters in 2008. Cities on the north side of Lake Washington had also unsuccessfully requested funds to study transit options for the SR522 corridor in the package. Sound Transit updated its long-range plan in 2014 to prepare for a proposed third expansion package for the regional transit system. It included BRT on the I-405 corridor, which was also designated for potential rail expansion, and an unspecified form of high-capacity transit on SR522 and between Bothell and Kirkland. A
grassroots citizens' group named "522 Transit Now!" formed to lobby for the inclusion of a rapid transit line on the SR522 corridor in the expansion package. In August 2015, Sound Transit revised the preliminary list of projects in the package to include BRT on SR522 alongside I-405 and the Eastside Rail Corridor. BRT on the Eastside Rail Corridor was removed from consideration in 2016 due to protests from
Kirkland residents who lived near the
Cross Kirkland Corridor, a section of the rail line that had been converted to a
bicycle and walking trail. The Eastside Rail Corridor was instead included as a study corridor for a potential future package.
Approval and planning Funding for a BRT system on I-405 and SR522 was included in the
Sound Transit 3 package, a major ballot measure in 2016 to expand Sound Transit services across the region. The BRT element would cost an estimated $3billion in year-of-expenditure dollars and include 2,100 total parking spaces at various park-and-ride lots. The earlier draft of the plan had only allocated $341million towards a BRT program, which was protested by Eastside cities, especially
Renton. The Sound Transit 3 package was passed by voters in November 2016 and the BRT lines were initially scheduled to open in 2024. The I-405 lines would be contingent on completion of HOT lanes on the south half of the corridor, which was originally scheduled to begin in 2019 and finish in 2024. The Bellevue–Lynnwood HOT lanes had opened in 2015. The BRT system was named Stride in 2018 and given its own branding, which would be reflected in bus liveries and station designs. In 2020, the individual lines were given alphanumeric designations—with S as a prefix to the number—to differentiate from existing BRT services in the region that use either letters or colors. Stride lines will be colored gold on Sound Transit maps. Preliminary engineering and planning began in early 2018 with contracts awarded to
WSP USA and David Evans and Associates. A set of business access and transit lanes on SR522 began construction in 2019 and was completed in 2022 for use by the future Stride S3 Line. In 2019,
Washington State Department of Transportation (WSDOT) began construction of Renton–Bellevue HOT lanes on I-405, which includes a rebuilt interchange for the Stride S1 Line. Sound Transit completed environmental review for the S1 and S2 lines (on I-405) in September 2020 and the S3 Line (on SR522) in March 2021. The program was delayed by several years due to a systemwide budget shortfall caused by the
COVID-19 pandemic. In the 2021 realignment of the Sound Transit 3 program, the openings for the Stride lines was revised to 2026 and 2027, with park-and-ride projects delayed further to 2034 and 2044. Sound Transit adopted the final alignments and stations for the Stride lines in September 2021, along with the site of the proposed
bus base. The scheduled opening dates were delayed by another year due to increased project risks identified by Sound Transit. The first major project, the three-level Northeast 85th Street interchange and station in Kirkland, began construction in September 2023. It replaces an existing
cloverleaf interchange east of downtown Kirkland with two
roundabouts that segregate HOT lane traffic and include stops for the intersecting
RapidRide K Line. Construction on other stations is began in 2025 with the
Hoffman Construction Company as the general contractor for all Stride shelters and furnishings.
Guy F. Atkinson Construction was awarded the contract to construct the station platforms and roadway improvements, including a
queue jump lane in Bothell, for the S3Line in August 2025. Another contractor, Pivetta Brothers Construction, was awarded the $27million bid to construct stations on the S3 Line. The S3 Line project began construction in February 2026 and is scheduled to open in 2028. The S1 Line on the south half of I-405 is also scheduled to open in 2028; the S2 Line on the north half of I-405 is scheduled to open in 2029. The Stride system is projected to carry 19,200 to 25,800 passengers on the I-405 corridor. ==Lines==