Seattle’s Light Rail Expansion Draws New Riders and Controversy

It’s not easy to run a train across a floating bridge. To extend light rail service across the mile-long stretch of Lake Washington that separates downtown Seattle from Mercer Island, engineers converted two lanes of the existing I-90 span to carry four-car electrified trains. That demanded a host of technical innovations, including a system of curved and rotating track supports that allow trains to adapt to the shifting movements of the bridge as it is buffeted by wind and waves.

According to regional transit agency Sound Transit, which operates the metro area’s Link system, it’s the first light rail in the world built on a floating bridge.

“If you ...