N.H. and Vt. Prevent Bridge Ice with High-Tech Sensor

Drivers heading into New Hampshire from Vermont on Interstate 89 this winter will have some high-tech help to keep them on the road.

Crews this week finished installing a sophisticated system that uses sensors to detect when ice is about to form on the I-89 bridge over the Connecticut River, then sprays the road surface with anti-icing fluid to prevent it from getting slick.

Denis Boisvert of New Hampshire’s Transportation Department is quick to point out that the fluid is not a de-icer, which melts ice that already has formed. It is an anti-icing chemical, which prevents it from forming in the first place.

“It’s a pre-emptive strike,” Boisvert said.

Sensors on the bridge deck and nearby track the temperature and moisture levels in the air and on the deck to predict when freezing is about to occur, and trigger a system of sprinklers embedded along the roadway’s centerline.

Each time the rain, snow or moisture on the surface approaches the freezing point, it will get another hit of potassium acetate.

Boisvert and his Vermont Agency of Transportation counterpart, Drew Gelfenbein, said the system is designed to prevent ice that road crews might not even know is about to form. It’s especially helpful on bridges over rivers, such as the I-89 bridge, where rising mist or moisture might cause black ice when nearby roads are clear and dry.

“When we have an icing condition like that, unfortunately, the road people may not know until there is an accident, because for the most part the roads are probably fine,” Gelfenbein said.

New Hampshire and Vermont picked the southbound I-89 bridge because of the icing probability, because it links two states interested in the project and has heavy traffic. The southbound side also is ideal because of its downhill approach, which makes it more difficult for drivers to stop if they hit ice.

The system is made by Boschung America of Newcastle, Pa., which has 40 systems either in place or in the works on roads and bridges in 15 states and one Canadian province, said the company’s director of business development, Bill Gorse. It also has been installed at numerous airports. Its parent company has installed about 200 systems throughout Europe.

The I-89 test is the first in the region.

“We’re just trying to install the first anti-icing system in New England so we can prove to those folks up there it is a reliable, viable solution for dangerous stretches of roadways and bridges,” Gorse said.

The company’s first fully automated system in the United States was installed on the I-35W bridge over the Mississippi River in Minneapolis in 1999, and officials who reviewed several years of accident data reported this year that icy weather accidents on the bridge were cut by 90 percent.

Now, they have a companion system on the I-35E bridge in St. Paul, said Christine Beckwith, maintenance research engineer with the Minnesota Department of Transportation.

“The system has been working really well,” Beckwith said. “Rarely do we have to intervene. They just work on their own.”

Ten Boschung systems are running in Pennsylvania, especially on bridges that tended to ice over, even in dry road conditions.

“We did see a marked decrease in the number of weather-related crashes on those bridges,” said PennDOT spokesman Steve Chizmar.

During night work on the I-89 bridge this month, nozzles were installed in a half inch-wide groove that crews cut all the way across the 850-foot span. Transportation Department crews also built a pump house and a spot for a 6,000 gallon storage tank on the Vermont side of the bridge.

The states hope to have the system in use within 30 days, Boisvert said.

Because the system is installed only on the southbound side, crews salting, sanding and plowing the northbound lanes will immediately be able to compare how it’s working. New Hampshire is responsible for plowing and maintaining the bridge.

The system, Boisvert said, is not meant to clear snow, but it should help make the clearing easier.

“If you have a heavy snow event, you will have snow on the bridge,” Boisvert said. “The chemical on the deck will keep that snow from bonding to the deck,” which means it won’t stick and be packed down by traffic.

The system should provide a layer of slush beneath the snow, Boisvert said, allowing plows to clear right down to the road surface.

And the chemical, Boisvert said, is not harmful to vehicles or the bridge deck.

If the test works well, both states would like to install the system in other trouble spots.

“In any mountainous area there are a lot of rivers,” Gelfenbein said of Vermont, “so there’s potential for crossings over the Lamoille River or the Winooski River where you have these potential problems.”

Boisvert said spots in New Hampshire’s Seacoast, including the I-95 bridge to Maine, would be likely areas for future systems because of high moisture and fog.