Field-testing multiple factors that affect plowing and deicing
Stephen Druschel of Minnesota State University, Mankato, loves his students. In his presentation at the 18th Annual Road Salt Symposium, he said “They throw themselves at this work! They get $15/hour and $500 worth of gear, and they think they’ve died and gone to heaven!”
The students received this pay and got to work with the high-tech gear—motion-activated cameras—as they helped Druschel investigate the effectiveness and efficiency of snowplow blades and pavement deicers. “Effectiveness is keeping cars on the roadway,” said Druschel, ”and efficiency is about lowest cost, lowest labor—as well as environmental efficiency.”
“Every plow driver is a scientist,” said Druschel, a civil engineering professor. “They observe, hypothesize, test, and evaluate. It’s the scientific method— all done in the cab of a truck.” But Druschel wanted to go beyond behind-the-wheel science to perform controlled tests of the effectiveness and efficiency of various equipment, materials, and techniques.
Comparing cloud formation at different speeds
Druschel and his cadre of assistants did their research on lanes laid out in the large parking lots of Canterbury Downs and ValleyFair! in Shakopee, Minnesota, during the winters of 2013–14, 2015–16, and 2016–17. “On a typical day,” he said, “we deployed 40 cameras and took 10,000 time-lapse photos.” For example, Druschel compared cloud configurations coming from a plow at three different speeds (Figure 1).
“The clouding effect on the driver’s side is the one that really counts,” Druschel said. “That’s where the guy who can’t stand that you’re going so slow will try to pass the truck. If they go through a big cloud, they will have zero visibility for a moment—and if they cut in too soon, they’re going to hook the plow and it will be a very bad day for everybody. We found that small adjustments of the plow speed make a huge difference.”
Comparing cloud formation from different plow types
With help from Carver County Public Works, Druschel compared nine different plows on separate lanes for several factors. “This is geek heaven in the world of plows,” Druschel said. “We tried one-ways, dozer plows, poly plows, and different cutting edges.” For example, he showed that a one-way steel blade (Figure 2) produced a smaller cloud than a one-way poly blade (Figure 3).
“The poly plows don’t focus quite the same as a dedicated one-way,” Druschel said. “But they’re flexible and if you go through an intersection or a roundabout, you need a poly plow.”
Druschel also tested dozer plow blades (Figure 4). “The dozer plows give you a lot of flexibility,” Druschel said, “but the cast is not as tight. It entrains a lot of air and the cloud behind it is pretty miserable. The choice of equipment has a real impact.”
The effect of traffic on pavement deicing
Druschel and his assistants also tested the effect of traffic on the speed of pavement deicing. MnDOT plow drivers had reported that traffic, particularly truck traffic, could substantially improve roadway deicing. Their hypothesis was that the pressure of the vehicle creates closer physical contact between the salt grains and the snow and ice, particularly with lightly packed snow. Plow drivers also thought truck traffic might create better deicing than cars because truck tires are usually inflated to 90 psi, compared with 35 psi, which is typical for cars.
In Druschel’s test after a snowfall and at an air temperature of 28° F, two lanes were plowed and then treated with 600 pounds of rock salt per lane mile pre-wetted with 15 gallons per ton of 10% RG8 (90% salt brine). One lane received 10 passes by a car, and the other received 10 passes by a plow truck. Figure 5 shows some of the results.
The MnDOT plow drivers’ hunches were borne out: Traffic does help to accelerate deicing—and truck traffic has a better effect than car traffic. The same test was conducted on a day when the air temperature was 22° F with similar but somewhat reduced effect. Druschel concluded that temperature makes a difference and that traffic definitely accelerates deicing. “Cars help, but trucks are better,” he concluded. (For more on how traffic increases the efficiency of deicers, see related article.)
The above are just a few of the many tests conducted by Druschel and his student crews. Comprehensive technical reports are available from MnDOT.
— Richard L. Kronick, LTAP freelancer