Sound Transit’s Clever Solution for Crossing I-90

Sound Transit

In case you missed it, Mike Lindblom had a great piece in the Seattle times this past weekend about the final engineering plans for East link on I-90:

Engineers have to ensure the bridge will remain buoyant when a pair of 300-ton trains pass each other, and that the high-voltage current that powers the trains won't stray into the bridge's pontoons and corrode its steel rebar. They spent $53 million just to design the section across Lake Washington.

The most difficult task is adapting the rails to the movements of the bridge.

Train tracks will cross the hinges and sloping spans between the bridge's fixed sections and the 1-mile floating deck, like someone walking down the gangway to a boat marina.

Click over to the article for detailed graphics on how it all works, but the gist is that engineers have devised a clever series of bearings to keep the train on the tracks as the bridge bobs, weaves and twists in the wind.

Also noteworthy: the design will allow the trains to cross the bridge at 55mph. Earlier plans had called for slower speeds (35mph) across the bridge. While it probably won't make a huge difference in travel time, it might have a psychological effect. Seeing a train blow past at 55mph while you're stuck in traffic could give someone more incentive to switch to transit.