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Improving Iowa’s Winter Road Conditions

Coralville Dam spillway

The Coralville Dam spillway during the 2014 flooding. In the winter, the area is covered in ice.

Wilf Nixon could see his breath as he climbed into the passenger seat of the orange snowplow truck on the ice-covered spillway of the Coralville Dam. Nixon, an IIHR research engineer, had arranged for the spillway to be flooded to measure the forces on an underbody plow blade as it cut ice. The driver started the engine, and as the truck began to move, Nixon looked out the windshield at the winter landscape. Suddenly, the scenery began to blur. Picking up speed, the driver began a turn — a bit too hard, a bit too fast. Nixon grabbed for the armrest as the truck spun out of control, turning, turning, until it finally came to rest after a full 360 degree rotation.

“It was interesting, let’s put it that way,” Nixon laughs. The driver was able to stop by putting the blade down — an advantage that ordinary cars do not have. Nixon, who is also a professor of civil and environmental engineering at the University of Iowa, focuses his research on ice, particularly as it relates to winter maintenance on roads and highways.

The Study of Ice

Nixon has been working on ice-related research since his PhD studies at Cambridge University. A native of Great Britain, Nixon grew up just north of London. After graduating from Cambridge, he came to the United States for a postdoc and was later invited to work with Jack Kennedy on ice research at IIHR. Kennedy was an inspiration for Nixon. “Talk about pioneering figures in a field!” he says. “Without a doubt, he was one.”

Ice has lost none of its fascination for Nixon, despite 30 years of research. His focus on transportation-related issues began about 1990, when he studied the optimum shape for the cutting edges on snowplow blades. After experimentation in the lab, Nixon instrumented some Iowa Department of Transportation (DOT) snowplows and headed out on the roads for fieldwork, which turned out to be an extremely challenging prospect.

“If you really want to break something, put it on a snowplow,” Nixon laughs. Many of the sensors and computers just couldn’t take the intense vibrations — they were shaken to bits. Several knotty problems had to be worked out before the research could proceed.

Wilf Nixon Iowa DOT

Wilf Nixon’s research helps keep winter motorists safe and roads open.

Iowa’s Winter Road Conditions

The team began work on a set of guidelines for snowplow drivers, such as when to adjust the angle of the blade. Another issue they considered was the two-to-one mix of sand to salt most DOTs were using in the early 1990s. Nixon and his team wondered, what is the sand really doing for us? The truth is, sand does little to improve winter road conditions. “More often than not, the reason they were putting sand down was so the public would know that the trucks had been there,” Nixon says. Salt, on the other hand, works very well. In Iowa City, Nixon says, road crews now use straight salt, but they pre-treat it with a liquid that gives it a brown appearance. People know the pavement has been treated, and may even think there is sand on the road, but in fact, it’s just salt. “I think there’s a good psychological value to that,” Nixon says. “It’s kind of sneaky.”

But salt, too, has its limitations. When the pavement gets too cold, salt doesn’t work at all, and is simply swept away by the next plow. When snow is wet and sloppy, drivers have to apply more salt to get the desired result. Another question to consider: How long will it be before another truck passes over this same stretch of road? All of these issues affect how much salt should be applied.

Nixon’s team also learned that prevention is better than cure for winter road maintenance. Putting salt on the pavement before the storm begins is about four times more efficient than waiting until snow has already frozen to the road.

Salt, of course, has its downsides — it harms plants and water quality. In the Chicago area, the Illinois EPA refused to grant permission for a new freeway near the O’Hare Airport until the toll road authority took steps to reduce chloride use. With Nixon’s help, Illinois is now starting to use less salt on its roadways. The Iowa DOT has been prudent about salt application, Nixon says, and consequently Iowa hasn’t seen the same level of chloride contamination as Illinois.

Snow in the South

Changing weather patterns due to climate change have made the job of winter road maintenance a lot harder, Nixon says. For example, two winter storms struck Atlanta last winter, an area that has rarely had to deal with serious winter weather. The first storm dropped less than three inches of snow, but nonetheless wrought disastrous results and left thousands of people stranded on the freeway, at work, or at school. Nixon says authorities knew the storm was coming and should have taken steps to prepare sooner than they did.

When the next storm arrived, Atlanta authorities basically shut the city down. No one went anywhere. Better, perhaps, than the first scenario, but Nixon says that each storm cost the region at least a half a billion dollars in lost economic activity.

If Georgia keeps on getting these sorts of storms, Nixon says, officials there can’t afford to continue dealing with them this way.

Was last winter an anomaly, or is it the new normal? No one can say for sure. “For a city like Atlanta, it’s a huge problem,” Nixon says. Can the area afford to take an economic hit like that again and again? Should officials invest in costly fleets of snowplow trucks? Atlanta and other cities need to conduct a risk analysis, Nixon says, to study the issues that will likely affect their future.

Iowa DOT Improves Winter Driving

Nixon has engaged in a very productive partnership with the Iowa DOT that has lasted more than 20 years. Nixon says he is impressed with a set of charts developed by DOT snowplow operators that are now found in the cab of every Iowa DOT snowplow. Drivers use the charts to determine how much salt to apply given the pavement temperature, the type of winter storm, and other variables. Using these guidelines, the Iowa DOT has been able to significantly reduce the amount of salt used. Other agencies around the country have also begun to follow the guidelines.

Another very proactive move by the Iowa DOT, Nixon says, was the installation of GPS in all their trucks. “I thought it was just brilliant,” he says. During winter storms, GPS data from the trucks is available on the web. Iowans can see where the trucks are, how fast they’re going, and what they’re doing – are they putting down salt? Is the plow up or down? About 400 of the DOT’s 1,000 trucks will also have cameras that will send an image about every five minutes; these will also be available on the web (accessible at The goal, Nixon says, is to provide motorists with more information about conditions so they can make rational choices about whether or not to hit the road.

Another new development is the use of vehicle speeds as a measure of winter maintenance performance during storms. By using cell phone signals, the DOT can determine how much drivers are slowing down because of the storm. This information becomes a potential tool to measure what’s really happening on the roadways. The best part, Nixon says, is that this research began as a UI student’s PhD project. The DOT adapted the research into a real-world application that will allow the agency to better serve the public.

Providing drivers with more information as they prepare to venture out on the road is one of the most important developments in winter road maintenance, Nixon says. “Figuring out that we really shouldn’t be out on the road is not something we find easy,” he admits.

And as for himself, except for that one exciting moment on the Coralville Dam spillway, Nixon has never had a winter weather-related accident. “Touch wood,” he adds, with a smile.

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Last modified on July 2nd, 2015
Posted on July 2nd, 2015

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