Seattle's 2 Line makes history as the world's first light rail on a floating bridge.

Countries & Cities · Published 15 October 2026 Swipe more like this →

In short: Crossing Lake Washington, the 2 Line represents a massive engineering feat. By integrating specialized track bridges that accommodate the constant, multi-directional movement of a floating structure, Sound Transit successfully linked Seattle to the Eastside. This transit milestone overcame years of intense political debate, legal challenges, and complex seismic design requirements.

The 2 Line is a 33-mile light rail system connecting Snohomish County, Seattle, and the Eastside region of King County. Its most notable feature is the use of the Homer M. Hadley Memorial Bridge, an Interstate 90 floating bridge. While early transit concepts for the region appeared in the 1960s, the project was officially set in motion by the 2008 Sound Transit 2 public vote. The line opened in stages, with the full route becoming operational on March 28, 2026.

Engineering a railway over a floating bridge required solving the problem of the structure's six ranges of motion. Engineers designed 43-foot-long track bridges featuring curved steel platforms and pivoting bearings. These components allow the tracks to remain stable during seismic events and adjust to lake level fluctuations or bridge deck movement. The system is so sensitive that trains must halt during high-wind events, specifically gusts reaching 40 miles per hour from the north or 50 miles per hour from the south.

The project faced significant hurdles, including a series of lawsuits from developer Kemper Freeman, who challenged the use of gas tax-funded infrastructure for rail. The Washington State Supreme Court ultimately ruled in 2013 that the conversion was constitutional. Additionally, the Bellevue City Council spent years debating the line's alignment, with disagreements over tunnel segments and surface routes causing delays. The final design, which included seismic upgrades and specialized steel frames within the pontoons, added $225 million to the construction budget.

By 2030, the 2 Line is projected to serve 50,000 daily riders. Its completion marks the culmination of decades of regional planning, starting from the 1976 agreement to reserve space for transit on the I-90 bridge. The project's innovative track bridge design was recognized in 2017 by Popular Science magazine, highlighting the technical ingenuity required to turn a decades-old transit dream into a functional reality for the Seattle metropolitan area.

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