Seattle Now It took years to float a train over Lake Washington. Here's how it works
Mar 30, 2026
Travis Thonstad, a UW civil and environmental engineering professor who helped design and test the light rail trackbridge, explains the years-long effort. He discusses floating-bridge movements and why joining rigid rail to a moving deck was tricky. Hear about early prototypes, full-scale testing, clever flexible-track solutions, ballast adjustments during construction, and long-term sensor monitoring and a digital twin.
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Floating Bridge Movement Creates Unique Rail Challenge
- Floating bridges move in three ways that matter for trains: vertical (heave), lateral (sway), and torsional (twist).
- Travis Thonstad explains cars tolerate those transitions but trains cannot handle sharp geometry changes without engineered smoothing.
Coffee Cup Prototype Gave The Key Idea
- Engineers prototyped an elegant transition device inspired by a coffee cup demo to force rails into a smooth curve across the joint.
- Andy Fone's half coffee cup and stir-straw mockup convinced the team it could pass trains up to 55 mph smoothly.
Multi-Stage Testing Turned Concept Into Reliable Design
- The design was validated through staged testing from UW labs to full-size trials at Pueblo's Transportation Technology Center.
- Tests revealed stiffness, maintenance needs, and informed final adjustments before installation on I-90.