How do you construct a rail line across a floating bridge?

By 2023, Sound Transit’s link light rail is scheduled to run from Seattle to Mercer Island, then on to Bellevue and Redmond. But there's one major hurdle -- there's a lake in the way.

The East Link light rail line is slated to cross the I-90 floating bridge over Lake Washington.

“It’s a challenge, and it’s fun…and it pulls out your hair sometimes,” said John Sleavin, Sound Transit’s deputy executive director.

In this talk, he explains the unique engineering challenges involved in moving a rail system with upwards of 52,000 daily passengers over the I-90 floating bridge. It’s something that hasn’t been done before anywhere in the world.

You’ll hear answers to questions such as:

What is post-tensioning?

Why are accordion joints, cesura components, and point distribution important?

How do you account for wind, waves, and lake levels?

What is the life expectancy of the bridge, and what might happen during an earthquake?

This episode of Speakers Forum is part of KUOW’s ongoing partnership with the Pacific Science Center in their Science in the City series. John Sleavin gave this talk at The PACCAR IMAX Theater on December 3, 2019.