Fortunately, help in meeting this challenge appears to be at hand with the new tool known as anti-icing. Based on a recent, informal survey by Dow Chemical Co., Midland, Mich., a large number of snowbelt states are embracing this new practice.
Anti-icing involves applying a relatively small amount of liquid chemicals or prewet rock salt to pavements in advance of freezing precipitation to melt snow on contact and/or prevent a strong bond from forming between frost or snow and the pavement surface. In cases of light precipitation, the anti-icing treatment may be all that is required to maintain bare pavement conditions. In cases of heavier snows, this practice makes it easier to plow to bare pavement.
FHWA study leads the way
The anti-icing concept received a big boost as the result of the Federal Highway Administration's (FHWA) Test and Evaluation Project 28, a four-year study to determine the conditions under which anti-icing is most effective. The study included participation by 15 states and concluded anti-icing "has the potential to provide the benefit of increased traffic safety at the lowest cost." The study resulted in the development of a manual for anti-icing operations in June 1996.
Summary application guidelines from the Manual of Practices for an Effective Highway Anti-icing Program (U.S. Federal Highway Administration, 1996) follow.
Light snowstorm
In temperatures at 20 degrees F and higher, liquid chemicals or prewetted solid chemicals should be applied at a rate of 100 lb per lane mile. Subsequently, the roads should be plowed as needed and an additional 100 lb per lane mile should be applied.
For light snow storms with periods of moderate or heavy snow, increase the second chemical application to 200 lb per lane mile. Applications will need to be more frequent at lower temperatures and higher snowfall rates.
Moderate or heavy snow
For temperatures around 30 degrees F or higher, liquid or prewetted solid chemicals should be applied at a rate of 100 lb per lane mile. The accumulated snow should be plowed and additional chemicals should be applied as needed. For temperatures in the 25 to 30 degrees F range, increase the initial chemical application to 200 lb per lane mile. If the desired plowing/treatment frequency cannot be maintained, spread rates may be doubled to accommodate longer operational cycles.
Frost or black ice
In conditions of frost or black ice, it is important to note traffic conditions when considering treatment. At temperatures of 28 to 35 degrees F, apply prewetted solid chemical when the traffic rate is less than 100 vehicles per hour. Liquid chemicals may be applied when the traffic rate is greater than 100 vehicles per hour. However, do not apply liquids if the ice is so thick that the pavement cannot be seen.
Both liquids or prewetted solid chemicals should be spread at a rate of 25 to 65 lb per lane mile. Be sure to monitor the pavement closely under these conditions. If thin ice forms, reapply the chemical at a higher rate.
Liquid chemical use on the rise
Even though the anti-icing strategy is very new, many states have already incorporated the practice into their overall snowfighting strategies. As a manufacturer of liquid calcium chloride, Dow routinely monitors state practices and recently contacted 20 state DOTs to track snowfighting strategies. Results of the company's poll are detailed.
Trend projected to continue
According to Jim Gall, Dow senior development chemist, conversations with states that are not currently using the anti-icing strategy indicate they may soon.
"In every case, interest in anti-icing is high. Almost every state we spoke with indicated they will look more closely at this strategy. As many concluded, public demand for bare pavement conditions and increasing pressure on budgets makes anti-icing an attractive concept.
"They must seriously consider anything that can get the job done and save money in the process. Right now it's a matter of local testing and refining the FHWA guidelines which, of necessity, are very general. Overall, though, the states we spoke with are bullish on the anti-icing concept."
