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‘Extremely rare’ wind event could stall light rail over I-90

Because Sound Transit's light rail trains will run alongside the north I-90 bridge, it will take strong winds from the north to impact service. (WSDOT)

It was a bit disconcerting to hear that light rail service from Seattle to the Eastside would be weather-dependent.

RELATED: The budget story behind the East Link light rail over I-90

Sound Transit East Link Executive Director Ron Lewis said the following about the service over Lake Washington on I-90 bridge:

“We did find that in events where there are storms with sustained high winds, we will back off on light-rail operations,” he said. “At present, we are looking at about 35 mph sustained wind from the north, at which point we would only operate one train at a time in each direction.”

And if sustained winds exceed 40 mph, service would be temporarily halted.

Lewis made sure to note that he’s mainly talking about winds from the north that cause waves to really slam up against the floating bridge. The light rail tracks will be connected to I-90’s north side of the bridge. Those wind events, he explained, are rare.

It looks like Sound Transit did its homework on this one because the National Weather Service in Seattle says the same thing.

Meteorologist Josh Smith says it is a rare event to get winds that strong over Lake Washington, especially from the north.

“We would need a really strong arctic outbreak for that to happen with air coming down through the Fraser Valley,” Smith said. “And then to get 40 mph sustained wind or more, we would need to get some sort of low-pressure system coming in at the same time, and that is just an extremely rare event.”

By “extremely rare,” Smith is saying every few years at the most.

“We haven’t looked at this quantitatively, but I would say it’s a rare event,” he added. “Only a few times we can remember that might have happened over Lake Washington.”

The majority of our wind events are from the south, including our strongest winds. That still has the potential to impact light rail service once construction is complete and the trains begin operating at a target date of 2023.

Lewis noted as much. He says southerly winds would have to reach about 50 mph before trains would be affected. That’s something that can happen a few times per year — at least.

“It depends on the year, of course,” Smith added.

And if winds were that strong, Sound Transit officials wouldn’t be the only ones looking at suspending bridge service. According to the Washington State Department of Transportation, the I-90 bridges are closed if wind speeds reach 65 mph for 15 minutes, or if conditions are deemed unsafe for to the public.

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