Winter storms can create slippery pavements and make driving hazardous. Each year, state highway agencies spend about $1.5 billion plowing, salting, and sanding their roadways to keep them safe for motorists. But what if we could prevent snow, ice, and frost from sticking to the pavement in the first place? We would not only have safer roadways, but we would also save money and use less salt, sand, and other materials.

A Revolutionary Concept

Anti-icing is a revolutionary new strategy for preventing a strong bond from forming between snow or frost and the pavement surface. It involves applying a chemical that will lower the temperature at which water freezes. If the snow can be prevented from bonding to the pavement, the roadway will remain wet or slushy, rather than icy. Motorists will be better able to control their vehicles -- thus making traveling safer.

Most highway agencies in the United States today rely on a deicing strategy -- as opposed to an anti-icing strategy -- on roads that receive chemical treatments. Deicing operations involve breaking the bond between the pavement and the snow and frost on its surface.

Although effective, deicing operations are not always efficient. A lack of site-specific, detailed weather information results in many highway agencies waiting until a storm hits to send out their work crews to salt, sand, and plow. But by then, the storm already has the advantage, and crews struggle to keep up and to clear pavements that are already covered with snow or frost.

In contrast, anti-icing operations usually begin before or just as a storm hits. Using new, sophisticated weather information technologies that include road weather information systems, highway agencies can pinpoint when and where to begin anti-icing operations. For example, a chemical that lowers the freezing point of water is uniformly spread across the pavement just before, or just as, the first snowflakes begin to fall. Depending on the strength and duration of the storm, the chemical might need to be periodically reapplied. Such anti-icing strategies help keep roads safe for travel, reduce the environmental impact of winter operations, and make post-storm clean-up easier.

European countries have been successfully conducting anti-icing operations for several years now. Through a cooperative technical exchange program, they have shared their knowledge with highway agencies in the United States. Their experiences were used in the development of an anti-icing test and evaluation project sponsored by the Federal Highway Administration (FHWA).

Field Testing

Since the winter of 1993-94, 15 states -- representing about half of those states with significant winter maintenance programs -- have been participating in FHWA's test and evaluation project to determine the effectiveness of anti-icing operations. The study is a continuation, with some modifications, of an anti-icing study initiated under the now-completed Strategic Highway Research Program. Technical support for the test and evaluation project is being provided by the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL), located in Hanover, N.H. CRREL is responsible for analyzing the data collected by the states.

The states experiences will help determine the conditions under which anti-icing is most effective, as well as the strategies or techniques that hold the greatest potential for success in a broad range of topographic, climatic, and traffic conditions. The evaluations will continue through the 1994-95 winter; a final report on the project is due next fall.

The key to a successful anti-icing strategy is knowing which chemical to use, in which amount, and when. Answering these questions is not simple. A highway agency needs real-time, localized weather information, as well as accurate forecasts for specific corridors.

There is no one solution for all conditions. The optimum strategy will vary depending on a site's conditions, such as weather, geography, and traffic. Candidate chemicals for anti-icing operations include liquid calcium magnesium acetate (CMA), liquid calcium chloride, liquid magnesium chloride, liquid sodium chloride (salt brine), liquid potassium acetate, and prewetted solid sodium chloride (NaCl, commonly known as rock salt).

The technology for applying the chemicals is also being examined. For example, several sites are using innovative material spreaders to apply liquid and prewetted materials. This equipment is capable of varying the spreading rate, spreading width, and prewetting rate upon demand, while correlating the application rate with the vehicle speed.

Results to Date

At an FHWA-sponsored conference in Minneapolis in August 1994, the 15 states participating in the test and evaluation recounted their first-year experiences. In general, they were enthusiastic about anti-icing operations, having found that these operations can:

• Reduce the amounts of chemicals needed.
• Prevent black ice or frost on bridge decks when liquid chemicals are periodically applied.
• Require less effort to return the pavement to a bare condition at the end of a storm.
• Reduce the amount of abrasives (sand) used.

In short, safe driving conditions can be maintained with less materials; this translates directly into reduced environmental and operational costs. Also, with the development of anti-icing technologies, additional options will be available to highway agencies to help them match their unique winter maintenance needs with specific conditions.

The states cautioned, however, that effective anti-icing operations require better weather information systems, improved materials and material spreaders, and more crew training. The potential savings in time and materials are great, but they won't and can't be realized overnight.

For more information about anti-icing strategies and technologies, as well as about FHWA's ongoing test and evaluation project, contact Andrew Mergenmeier, FHWA Office of Engineering, at (202) 366-1557 or fax (202) 366-9981.

Andrew Mergenmeier is a highway engineer working in the Construction and Maintenance Division of FHWA's Office of Engineering. His primary responsibilities include technical and program assistance on construction and maintenance issues. He is the project manager for the anti-icing technology test and evaluation project, and last August, he hosted a national conference on this subject. In spring 1994, he was co-chairman of a joint American Association of State Highway and Transportation Officials (AASHTO)-FHWA international winter maintenance technology scan of Japan and several European countries. Mr. Mergenmeier holds a bachelor's degree in civil engineering from the University of Kansas and is a registered professional engineer.