Saturday, February 17, 2018

New wind and wave criteria changes threshold for potential closures of the westbound I-90 floating bridge

Updated Sept. 20, 2018

By Annie Johnson and Harmony Weinberg

Changes to how we react to wind on the I-90 Homer M. Hadley Floating Bridge could mean a temporary closure during high wind events. This bridge carries westbound I-90 traffic, the future Sound Transit light rail tracks and the I-90 Trail.

If we hit a new threshold of sustained winds from the north of at least 40 mph, (or 45 mph wind from any direction) for one minute, we will not allow traffic onto the westbound I-90 bridge between Mercer Island and Seattle. Emergency vehicles will have access to the bridge at all times.

Why the change?
Wind and wave analyses performed during Sound Transit's East Link design process showed the pontoons on the westbound I-90 bridge are susceptible to damage during strong north wind events.

It's important to note that there is no immediate safety risk to the public or the bridge. However, any damage caused by strong north winds can shorten the life of the bridge.

Our Bridge Preservation Office used the analysis from Sound Transit to determine the criteria in order to preserve the life of the westbound I-90 floating bridge.

How much notice will travelers receive in the event of a westbound I-90 closure?
We will give as much notice as possible about potential closures, however, we will not close the road until the wind criteria is met. Once that happens, we can close the roadway in about 15 minutes. We will use social media, our mobile app and overhead message signs to alert travelers.

As is the case with any emergency closure, whether it's due to multiple spin outs on Snoqualmie Pass or a major collision, we all need to be prepared for delays whenever we hit the road. We will continue to do our best to keep you informed of any and all closures that could affect you. In the Seattle and Mercer Island areas, you can get real-time traffic information on your phone with the WSDOT traffic app, track the WSDOT Traffic Twitter feed and check out our Facebook page.

The backstory
I'm sure you're wondering how we got here and why the bridge hasn't closed in the past when we've had high winds.

The westbound I-90 floating bridge was designed in the late 1970s and built in the 1980s and, like our hairstyles and clothes, many things have changed in the world of floating bridge engineering since then. If we were to build a brand new I-90 bridge today, it would likely look significantly different that the I-90 floating bridges you drive across today.

It's not that today's bridge is unsafe or needs to be replaced but we've learned a lot over the past 40 years. We now have much higher 100-year- storm criteria and know more about local storm and wind patterns.

2 comments:

JRo said...

This was very informative. Thank you.

GW said...

How is it the eastbound lanes are not a issue from southerly winds, they were build around the same timeframe?

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