Construction of the so-called East Lake extension of the Seattle Light Rail system is about to start. The East Lake extension goes across one of Lake Washington’s floating bridges (the lake is too deep for a conventional bridge with pylons and spans). Seattle is on the west of Lake Washington; Bellevue and Redmond with its Microsoft campus are on the east side.
There are several forces that will cause significant movement in the giant bridge pontoons: two 300-ton trains passing each other, water movements in the lake due to tides and stormy weather, and even the tremors of an earthquake. So the engineering team has already spent lots of effort on coming up with a design that will accommodate the moving rail bed, so that the rail tracks will stay stable and parallel.