The new Sound Transit line between Seattle and Bellevue is the only passenger railway in the world built on a floating bridge. To construct it, engineers had to solve three major challenges: strengthening the pontoons supporting Interstate 90, developing special rail joints capable of keeping trains stable as the bridge moved, and creating protection systems against stray electrical currents that could damage the bridge structure and railway infrastructure.
Based on: To make light rail float, 3 big puzzles needed solutions