Featured Article: Intelligent vehicle systems defy bad weather
Better Roads Staff
“Feedback from plow drivers has sharpened the forecasters’ skills to predict weather in areas affected by distinct microclimates and mountain-induced unusual weather patterns,” Bernhard explains. “Using truck-mounted brooms for fighting snow is a local adaptation that has proven it’s worth it in this unique desert region.”
Tunneling Through Super-Cooled Fog
In northern Utah, super-cooled fog — less than 32 degrees Fahrenheit — can stay in the mountain valleys for weeks. Based on recommendations in a field trial report (the report is available at http://www.fhwa.dot.gov/weather/best_practices/CaseStudies/025.pdf) and lessons learned from anti-icing operations near Salt Lake International Airport, maintenance personnel configured a truck with fog dispersal equipment composed of commercial, off-the-shelf products. Going to this configuration was more cost-effective than the customized configuration developed by the Department of Meteorology at the University of Utah, which was prohibitively expensive, according to the report, “Best Practices for Road Weather Management, Version 2.0.”
Prior to the deployment of fog dispersal equipment in 2000, the DOT had developed a two-hour training course to ensure employee safety when working with compressed liquid carbon dioxide, including oxygen-displacement properties of the chemical, chemical handling techniques, and operation of the high-pressure dispenser.
Fog dispersal equipment is composed of commercially available products and is installed on about 70 maintenance vehicles for UDOT — about 15 percent of the fleet. Each truck is equipped with a compressed gas cylinder, a manual valve assembly mounting brackets, copper pipe and a dispensing nozzle. Each cylinder holds liquid carbon dioxide at a pressure of 2,000 pounds per square inch.
Nozzles are placed on top of a plow truck, explains Bill Hoffman, chief maintenance and operations engineer for the Nevada Department of Transportation. As the truck is driving its normal speed, the liquid carbon dioxide is dispersed up into the slipstream of the truck.
“The liquid CO2 crystallizes fog vapor particles so they drop out and are too heavy to stay in the air,” Hoffman says. “It creates a ‘tunnel.’” However, this doesn’t work if it rains or if there is fog that is too warm. Hoffman says it has to be done during the winter, “and the condition has to be pretty exact.”
The cost of magnesium chloride and potassium acetate has steady been rising so agencies have been looking to find an alternative or replacement. In Alaska, there is the added expense of everything needing to be shipped. ADOT&PF went the homemade route and began making its own brine in Sitka, Valdez and Juneau, Alaska. Next summer, the agency plans to install a salt brining unit in Fairbanks.
The significance? The Fairbanks area has never done anti-icing before. “It’s the interior part of Alaska, and in times past, summers have been 90 degrees [Fahrenheit], followed by two to three weeks of fall, and then by Oct. 1 temps fall to below zero and stay that way until April,” explains Michael J. Coffey, statewide maintenance and operations chief for the Alaska Department of Transportation and Public Facilities. It’s not uncommon for Fairbanks, to deal with temperatures 50 degrees below zero, he says. But during the past several years, the area has been getting more freeze-thaw cycles in the fall and spring. That means the transition from fall to winter used to be two to three weeks — possibly a month. Now that timeframe is six to seven weeks and includes freezing rain events. “That means we now have to do things differently,” Coffey notes. “We’ve done things differently by applying salt brine with a corrosion inhibitor, and it’s been a significant money saver.”
For more on homemade brine and an innovative salt slurry generator that’s used with it, see the June 2009 print edition of Better Roads and the December 2009 print edition for our Top 20 Products of 2009 (or go to http://www.betterroads.com/featured-article-the-2009-top-rollouts), in which this slurry spreader that uses homemade brine was featured.
Push a Plow, Pull a Plow
A very long trailer with a snowplow on it — i.e. a “tow plow” is enabling agencies to clear 2 to 2-1/2 lanes with just one operator. Before this equipment configuration was developed, the same job would have taken two passes and two people, says Bill Hoffman, chief maintenance and operations engineer for the Nevada Department of Transportation. Now one person can do the job by plowing in front with a traditional plow and in the back with a trailer, or “tow plow,” he says.
The equipment configuration isn’t brand new. The Missouri Department of Transportation (MoDOT) has been using it for two to three years (which is why the tow plow was originally dubbed the “Missouri Snow Plow”). But now it has moved beyond the Missouri borders and is being adopted by other agencies.
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