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Ways engineers may stop ice from falling off the Mackinac Bridge

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David Marvin
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Creative Commons

Off and on for the past several weeks, the Mackinac Bridge has been closed due to falling ice. Rick Brewer spoke with Matt Chynoweth, Chief Bridge Engineer for the Michigan Department of Transportation, to explain the complexities of the bridge and to discuss how this problem could be fixed in the future.

This transcript has been edited for clarity.

Rick Brewer: Matt, I'd like to start this conversation with you simply explaining what is happening on the Mackinac Bridge?

Matt Chynoweth: Well, so the question relative to the recent closures has to do with large pieces of ice that form on the towers and on the main cables. As we're entering spring, we're having temperature fluctuations. And since it's not a gradual kind of increase in temperature, where things can just kind of melt or the water can just drain down, we're getting large fluctuations in temperature. So large pieces of ice that will typically formed at the low sag parts of the cables and where the suspended cables connect to the main cables. Those just come off in large chunks. And because the cables are directly above the roadway, and we have high winds up there, it is not safe to have traffic on the bridge when this, we call it ice accretion. When these big sheets of ice fall off the structural elements of the bridge.

RB: What are some of the mitigation strategies you've looked into?

MC: The interesting thing about that is there is no industry standard in solving this icing issue. So, Michigan is in a fraternity of a lot of other states and even countries that have had this type of issue. Ohio's had it on the on their I-280 bridge over the Maumee. The Queensferry crossing in Scotland has been closed several times. And then there's two bridges in British Columbia, Canada, the Alex Fraser and the Port Mann bridges that have had the similar things, right, closure due to ice falling. And so there's been a lot of studies. And there's basically three things that we looked into on Mackinac Bridge. One of them is to try to heat like the towers and heat the cables, which, as you can imagine, a very large structure, those towers are like 30-story buildings above the bridge deck. And just think about the infrastructure we take to keep those at like 35 degrees. The other things we've looked at is different types of shapes that we can put on the elements themselves that don't lend themselves well for ponding water, or for ice formation. And then another thing that's got some promise, but requires quite a bit of additional analysis is this idea of having vibrational motors, that we can attach to these elements and actually vibrate them in certain weather conditions to prevent the formation of large pieces of ice. But again, the engineering to figure out what frequencies are needed to vibrate these elements without damaging them, but also creating an a vibration to prevent the formation of ice. That needs a lot more work. So all of these are very customized, and unfortunately, very expensive.

RB: When it comes to obtaining any type of funds for these costly enterprises. What is the Department of Transportation's routes that they're looking into?

MC: So when it comes to the Mackinac Bridge Authority, anything that's done on that bridge relative to maintenance, or even capital investments is from the tolling operations. So, if we decided to move forward with something like that, it would be up to the bridge authority to set up, you know, a specific program account that we can fund a specific project. That's how they do the painting projects on the bridge. That's how they're going to be doing the deck replacement in a couple of years. So that would be funded out of tolls. And then it just becomes a function of not only building whatever it is that we're going to do whatever piece of additional infrastructure, but then those lifecycle maintenance costs have to be added to the overall lifecycle maintenance costs of the overall bridge.

RB: What is your message to the public for people who are frustrated with the closures?

MC: Yeah, I mean, I definitely my messages. We absolutely empathize with the fact that they're, you know, we have no other alternate route. If the Mackinac Bridge is closed we know that people are stranded. And if we're dealing with these issues on a regular basis, then yeah, there's there's going to be more done to mitigate this so that we don't have to deal with the closures.

RB: Matt, thank you so much for taking the time to speak with me today.

MC: Okay, my pleasure.

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