Highway Deicing and
Anti-icing for Safety and Mobility

For latest developments, see our blogs for highway users and roadway maintainers/snowfighters.

Winter highway maintenance is a major market for salt, although that market is sometimes geographically distant from the production site and hard to resupply in the middle of winter, particularly after waterways freeze. 

It's easy to see why we need salt on winter roads.

Highways play a vital role in assuring personal and commercial mobility ( 1   2   3 ) and the productivity of the overall economy [See our 3.77 MB RealMedia video) as evidenced by the success of the U.S. Interstate Highway Program.   In the U.S., more than 70% of the roads (and 70% of  the population) are in snowy regions which receive more than 5-inches (13 cm) of snowfall annually   Investing in efficient highway operations leverages the larger investment in building highways in the first place and realizes their intended purpose.  In the U.S., the Federal Highway Administration manages highways to achieve highway user satisfaction in terms of mobility and productivity...and safety.  FHWA sees effective winter maintenance as essential to combating roadway congestion and a core highway operations priority (see the FHWA slide show) and new highway statistics-gathering efforts are expected to focus management attention on improving highway operations.  The same is true in Canada.  Many states are implementing outcomes/performance measures to judge their snowfighting effectiveness.

Good highways are safe highways too.  Safety as well as mobility can be jeopardized by poor highway design and construction or by operating procedures which allow unsafe driving conditions -- such as construction work zones, incident management or response to weather emergencies.  One-third of all traffic crashes are highway related -- half of them, 17% of the total, weather-related.  More than 7,000 deaths and 800,000 injuries on U.S. roads every year are weather-related.  A recent study of Iowa freeways found that winter storms increase the crash rate by 1300%!  A major study, Improving Roadway Safety: Current Issues by Mark Edwards, identifies "temporary friction enhancement" through deicing as an effective safety countermeasure.  The Roadway Safety Foundation agrees. A 2004 study by the economic consulting firm Global Insight, Inc. found enormous costs associated with blizzards which might shut down various states and provinces including Iowa, Illinois, Indiana, Michigan, Minnesota, Missouri, New Jersey, New York, Ohio, Pennsylvania, Virginia, Wisconsin...Ontario and Quebec. The methodology might be applied to other states and provinces."   Measures such as the "travel rate index" help highway users and highway agencies assess the operating efficiency of their roadways.  Highways play a vital role in our society and economy.

Salt was first used in the 1930s in snow and ice control to make roads safe and passable, although snowfighting has a long history, personal reminiscences of a retired snowfighter online in an easy-to-listen-to (but not short) podcast.    It wasn't until the Sixties that the use of salt in conjunction with plowing became widespread after winter maintenance personnel learned of its effectiveness.  Confined originally to the "snow belt," snowfighting is now a priority activity in the Sunbelt too.  There is now a vast international experience in effective snowfighting and the elements of successful plans for snowfighting.  The public demands safe winter roads ( 1   2 )  making an investment in effective winter maintenance manages risk and is good politics.    Remember Michael Bilandic?! 

Today, salt is a necessary and generally accepted part of the winter environment. It provides safety and essential mobility for motorists, commercial vehicles and police, fire and other emergency vehicles. In fact, if responsible agencies fail to keep their roadways clear of ice and snow, they can be sued -- successfully (homeowners, too, have a responsibility to keep sidewalks ( 1    2 ) cleared.    Agencies strive mightily to assure they have enough salt to meet their winter maintenance needs.  State/provincial and local transportation agencies have the lead, though an increasing number are using private contract winter maintenance service providers.   The Transportation Association of Canada has a good primer on snowfighting.   Some provinces and states, like the states of  Wisconsin    ( 1     2 ), Iowa ( 1   2   3 ), Nebraska, Washington, Maryland, West Virginia ( 1    2 ), California, Colorado and the province of Ontario, provide public reports online about their services and, in the case of Ontario, both general winter maintenance technologies and  their progress implementing new snow and ice technology solutions.  Pittsburgh, PA, Montreal, QC, Minneapolis, MN, Charlotte, NC and Howard County, MD are examples of cities which provide cyber-notice to its citizens about its Snow & Ice Program. Indianapolis, IN also has a great page under Department of Public Works.  Nor is this a North American phenomenon; Sapporo, Japan, for example, does the same.

Road weather (specifically, "microweather" at the roadway surface) is key.   See how North Dakota has harnessed its road weather system. Whether you get your weather information from the National Weather Service, specialized traffic/weather websites (e.g. SmartTraveler and Northwest Weather Consultants), the Federal Highway Administration's new FORETELL program, a traveler's information website or the Farmer's Almanac snow and ice are predictable occurances in much of North America.  Real-time roadway surface conditions can be tracked with mobile friction-testing devices and embedded sensors.  Truckers who must deliver their often-time-sensitive cargos are also vitally concerned about road weather conditions.    Road weather is an important part of the nation's research agenda and a priority focus for professional meteorologists.   Many highway maintenance organizations in the U.S., Canada, Japan and Europe especially, depend on detailed weather forecasts, road weather information systems (RWIS) and weather cameras on both bridges and highways ( 1    2 ) to plan their snowfighting operations and use newer techniques like anti-icing.  In the U.S., the multi-agency Aurora Project is coordinating RWIS research and the Federal Highway Administration and National Oceanographic and Atmospheric Administration are cooperating in synthesizing RWIS data.   Effective snowfighting depends on salt; without salt, there would often be hazardous conditions and even chaos. Yet its use has brought criticism, sometimes justified in the past, when it was used to excess.

When salt is used properly, it does not present environmental harm. And, besides the socio-economic benefits of mobility and safety, treating winter roadways with salt has environmental benefits of reducing air pollution by avoiding congestion and by eliminating use of sand and other abrasives which contribute to airborne particulate pollution and runoff into roadside streams.   The potential for adverse environmental impacts of salt, however, is well recognized, particularly in areas immediately adjacent to roadways.  These impacts include impacts on wildlife habitat and vegetation as well as contributing to corrosion of vehicles and infrastructure.  The issues of highway salt's environmental impacts have been studied extensively over the past half century. In 1991, the National Academy of Sciences' Transportation Research Board conducted an extensive review of these issues and concluded, in its Special Report #235, that salt will remain the deicer of choice for the foreseeable future.  The Michigan DOT agreed.  Finland conducted a similar environmental review with the same result:  it recommended continued use of salt at current application rates.  Canada has a comprehensives salt management Code of Practice.  Runoff from salt applied to highways, except in unusual local circumstances, is not a general problem, as the Federal Highway Administration concluded in a report issued in 2000.  Of particular concern, however, is the need for proper salt storage during industry distribution and by customer transportation agencies.  Salinity is much studied, particularly regarding irrigated lands, salt-tolerant native species, and plant species that remove salt from the environment ( 1     2     3     4     5     6 ).  New technologies hope to reclaim saline soils and develop salt-tolerant plants and commercial crops.  The impacts of salt on various plant species ( 1    2 ) and soil have been studied extensively by the U.S. Department of Agriculture's Salinity Laboratory and is well understood. Ongoing reviews suggest proper management is necessary, but sufficient, to protect the environment. For a summary, see our publication Highway Salt and Our Environment ( free download in English and French).

Snowfighting is a profession and this requires planning, proper equipment, training and preparation.   Winter maintenance practices are grounded on a significant body of research, including reports from the Strategic Highway Research Program, SHRP.   Traditionally, salt has been used to deice roadways, but winter maintenance organizations are now devoting new priority to advanced technologies and to anti-icing, the preventive, pre- or early-storm treatments (using pre-wet solids or liquid deicers) to prevent the loss of safe driving conditions.  Some bridges can even anti-ice themselves!  Many research projects are underway and recently completed.  And new technologies such as use of Global Positioning Systems (GPS) are finding winter maintenance applications -- even artificial intelligence software has developed for snowfighting!  One key advance enabling this strategy is the development of better weather forecasting and more effective road-weather information systems (RWIS).  RWIS data is used by snowfighters, but also being shared with the driving public ( 1     2 ).    Salt (sodium chloride) brine is increasingly used to pre-wet highway salt before applying it to roadways.  Most agencies make their own brine.  And better "micro" weather forecasting enables preventive pre- or early-storm treatments called anti-icing.  The Maintenance subcommittee of the American Association of State Highway and Transportation Officials (AASHTO) is coordinating major research on effective anti-icing through its Snow and Ice Cooperative Program (SICOP).  SICOP has also published a study examining the costs and benefits of RIWIS and anti-icing.  The Roadway Safety Foundation, Federal Highway Administration and C-SHRP (Canadian-Strategic Highway Reseach Program) promote anti-icing too. States report success with the new anti-icing programs and other innovations.  So do Canadian provinces.  Need contacts?  And not all advice comes from official sources.

Why Is Salt Used?

Salt is used as the principal deicer because it is the most available and most cost-effective safe deicer. It is plentiful in the earth and the sea. The primary type used is rock salt that is mined from the earth. Solar salt, which is evaporated by the sun from seawater is also used. Some 15 million tons of deicing salt is used each year in the U.S. and about 4-5 million in Canada.  Even when its recognized risks to environment and infrastructure are factored-in, salt is the best option for snowfighting in its working range of over 15 degrees Fahrenheit/-8 degrees Celsius.

In today's highly mobile society, it is imperative to remove hazardous conditions created by snow and ice as quickly as possible and to keep roads open to guarantee essential mobility in winter. That makes a deicer necessary. Sometimes, salt is used alone when there is ice or too little snow to plow, mostly it is used in conjunction with snowplows.

Salt is used to keep snow and ice from bonding to the pavement and to allow snowplows to remove accumulations quickly and efficiently.  Professional applications are required to assure the deicer reduces slipperiness.

In short, salt is used to keep highways safe and passable. [See our 4.26 MB RealMedia video].  Research indicates that using salt, snowfighting crews can reduce accidents sharply.  A study by the Marquette University Department of Civil and Environmental Engineering documented injury accident reduction of 88.3%, paralleling findings of an earlier German study illustrated below.  Summaries are available in English and French.

How Does Salt Work?

When salt is applied to ice and snow it creates a brine that has a lower freezing temperature than the surrounding ice or snow. Salt is the ideal deicing material because it is

• readily available

• the least expensive deicer

• easy to store and handle

• easy to spread

• non-toxic

• harmless to skin and clothing

• harmless to the environment when used and stored properly

Professional Snowfighters in the U.S. and Canada are learning lessons from European snowfighters in the use of anti-icing to prevent the ice/pavement bond, not just destroy it.

Why Not Use Alternatives?

Alternative deicers are just not practical. Those that are as effective as salt are too expensive and have limited availability. Some have a very detrimental effect on the environment, and on pavements. According to a 1978 report on the technical, environmental and economic aspects of highway deicing salts by the National Conference of State Legislatures, "Several alternatives to deicing salts have been investigated or tried, but they tend to be too expensive, damaging to highway structures, more toxic than deicing salts or not as effective. The alternatives include other deicing chemicals, pavement heating systems, mobile thermal deicing systems and mechanical equipment." The conclusion is equally valid today.  Despite the futile search that has gone on for years for alternatives as effective, as inexpensive and as safe as salt, the search continues.

Abrasives are often cited as practical alternatives, but they have limitations ( 1   2 ).   Disadvantages of abrasives are that they cannot melt snow and ice, offer only temporary traction, are covered up by new snow, large quantities and frequent applications are necessary and they must be cleaned up at great expense. Abrasives are not cost-competive with salt ( 1    2 ) in most circumstances.  It is essential to use some salt with abrasives in order to keep the abrasive stockpile from freezing.

Straight salt is more efficient and more economical. Used sensibly, it is the best means of providing safe roads in winter by itself or in conjunction with plowing, depending on the situation.

Sensible Salting

The Salt Institute has a training program for public works personnel responsible for snowfighting operations: Sensible Salting. Sensible Salting emphasizes getting the most out of every application of deicing salt, maintaining the safest roads possible in the most economical way while protecting the environment.   The Transportation Association of Canada has produced nine Syntheses of Best Practices for managing highway salt available in both English and French:

A good Sensible Salting program should include

• Personnel training

• Good equipment

• Calibration of spreaders

• Use of automatic controls

• Adequate, covered storage

• Proper maintenance around storage areas

• An awareness of safeguarding the environment by all who use salt.

Anti-Caking Agents

Certain additives are put into salt to keep it from caking. The most frequently used is sodium ferrocyanide, also known as Yellow Prussiate of Soda (YPS). Another is ferric ferrocyanide, also known as Prussian Blue. They are added in amounts of 20 to 100 ppm.

YPS is approved by the Food and Drug Administration as an anti-caking additive in table salt based on exhaustive tests wherein no evidence of toxicity was demonstrated at levels considerably higher than those used in highway deicing salts. Prussian Blue is also used in household bluing, blueprints, blue-black ink and carpenter's chalk. It is also non-toxic to animal and plant life.

Corrosion

One of the major criticisms of salt is that it contributes to corrosion of metal. The basis of much of the environmental concern about salt can be traced to salt's acceleration of the corrosion of vehicles.

However, cars will rust even where deicing salt is not used, particularly in warm coastal areas and in wet climates. Automobile companies have intensified efforts to protect cars from corrosion by special dipping processes, use of aluminized waxes, zinc-rich primers, galvanized steel and greater use of other non-corrosive metals and plastics. [See our 2.36 MB RealMedia video].  In addition, some give the assembled cars an anti-corrosion treatment. Extended warranties by the major auto companies are now offered against rust perforation of automobiles. Car owners have a responsibility to help protect their cars from corrosion by touching up nicks and scratches, waxing frequently and washing cars regularly, even in winter.

Bridge deck corrosion has been a problem in the snow belt areas. Research on the subject is an ongoing process. Various anti-corrosion methods have been tried or are now available. The method offering the most promise for old bridge decks is cathodic protection, where a small reverse current halts the rusting process. Another approach is applying a sealant to the concrete.  Epoxy-coated reinforcing bars and air-entrained concrete and/or high-density concrete are used in the construction of new deck surfaces.

Homeowners sometimes worry about possible salt damage to concrete sidewalks and driveways (as well as grass and shrubs).   Correct application of deicers to properly-constructed concrete structures (e.g. air entrainment) limits these concerns.

Want more details?

Potholes

Salt has often been blamed for causing potholes. Potholes are caused by water entering the grade below the surface of the road and then freezing. This freezing cause the road surface to heave. Thawing leaves a cavity or weakened spot beneath the surface. Traffic then causes the surface to collapse into the cavity creating a pothole. Salt can cause surface spalling of poor concrete or scaling of non-air-entrained concrete. It has no bad effects on asphalt or the air-entrained concrete that is available today for road building. The State of Iowa has tested various deicing chemicals for their impacts on concrete highways and found sodium chloride "benign."  Better Roads magazine has an informative discussion on potholes.

Economic Benefits of Salting

Not everyone realizes all of salting's benefits. Consider these statistics:

A 1972 study by Paul J. Claffey, an independent consulting engineer, presented to the Highway Research Board (now Transportation Research Board) concluded that the roughness of road ice and slippage of wheels can result in an average one third more fuel consumption and as much as 50 percent more on just two inches of snow.

In a 1976 report, Benefits and Costs in the Use of Salt to Deice Highways, by The Institute for Safety Analysis (TISA), Washington, DC, using 1976 prices and rates, the use of deicing salt

• reduces wages lost due to lateness to work by $7.6 billion

• saves $3 billion in wage loss because of absenteeism

• reduces production losses by $7 billion

• reduces losses in goods shipment by $600 million

• saves 370 million to 1.2 billion gallons of fuel

• has an 18:1 benefit:cost ratio

A study, Accident Analysis of Ice Control Operations, released in 1992 by Marquette University's Department of Civil and Environmental Engineering concluded that "As a winter maintenance service, de-icing pays for itself within the first 25 minutes after the first hour that salt is spread on two-lane highways. . . .Then, during the first four hours after the hour of application of salt, the direct road user benefits were $6.50 for every $1.00 spent on direct maintenance costs for the operation." As soon as 71 vehicles drove over the highway, the average direct costs were offset by direct benefits. The study found that costs related to accidents, including medical expenses, emergency services, workplace costs, travel delay, property damage, and administration and legal expenses decrease by 88 percent after application of deicing salt.

Use of salt, in conjunction with a good plowing program, is the fastest and most efficient means of snow and ice removal. The use of abrasives requires at least seven times more material to treat a given distance of roadway. Therefore, it takes seven loads and seven round trips to the loading point, compared to just one for salt, resulting in a greater use of fuel, increased manpower and more time to treat roads during a storm. Studies by the Salt Institute have determined that a loaded salt truck, spreading at the generally accepted rate of 500 pounds per two-lane mile for general storm conditions, can treat a 22.5 mile stretch of roadway, traveling a total of 45 miles. A sand truck requires seven loads, must travel a total distance of 187 miles to treat the same section of road and that truck requires four times more fuel. In more ways than one, salt used in snow and ice control contributes to energy savings.

Using Salt Makes Highways Safe

While drivers and vehicles are often at fault, more than 30% of traffic crashes are due to roadway conditions.  The same Marquette University cited above concluded that the total number of accidents is 8 times higher before deicing than after on a two-lane roadway (4.5 times higher for multi-lane freeways), the number of accidents involving injuries is 9 times higher before application (7 times higher for multi-lane freeways), and the severity of accidents is reduced by 30 percent after application.

Although no specific statistics are available on the effects of storm-clogged roads on the delivery of emergency service (ambulance, fire, rescue and police), common sense tells us that response times are drastically affected by snow and ice covered streets. Consider the number of times you have heard the call go out over radio and television for volunteers with 4-wheel drive vehicles to transport medical professionals, deliver meals and medical supplies to the elderly and disabled, and otherwise fill in for needed public services affected by storms.

The public has a right to expect safe highways. . .even in the face of winter snow and ice storms. Public works professionals have the tools to restore safe and passable streets and highways.

In Summary

Salt is an essential part of the winter environment and its use is accepted by a great majority of the motoring public. It is one of the major weapons in the battle against snow and ice. It is used to provide safety and essential mobility on roads in winter. Salt is the most plentiful and most inexpensive deicer that is both efficient and safe. It is easy to handle. It is non-toxic to man and animals and will not harm the environment when properly used. Salt's benefits far outweigh any detrimental effects. The benefit-to-cost ratio is about 18 to one. Salt saves lives in reducing accidents, reducing response time to medical and other emergencies, provides energy savings by removing snow and ice quickly and reduces the size of economic losses that would otherwise mount up with snow and ice left on streets.

Snowfighting managers:  don't forget to visit http://www.saltinstitute.org/snowfighting for free training materials.

For further information, please contact the Salt Institute or see our page with additional FAQs about deicing salt, the Federal Highway Administration (snowfighting professionals, make sure you visit FHWA's Winter Maintenance Virtual Clearinghouse and its National Transportation Operations Coalition website), American Association of State Highway and Transportation Officials (and its guide on winter operations) and the SICOP Winter Maintenance Technical Services Program (including SICOP's list of Research in Progress), a state DOT winter maintenance research consortium, Clear Roads (including periodic podcasts on winter maintenance), American Public Works Association (and its Winter Maintenance Subcommittee, which as a great page of relevant links), Pacific Northwest Snowfighters, National Association of County Engineers, Transportation Association of Canada (including the TAC Code of Practice on Salt Management Plans and TAC's new salt management Learning Guide and train-the-trainer guide), the National Academy of Sciences' Transportation Research Board (including TRB's "Research in Progress" and proceedings of its quadrennial Snow & Ice Symposium), International Road Association (PIARC), National Safety Council, Canada Safety Council, Governors Highway Safety Organization, American Highway Users Alliance, Roadway Safety Foundation, The Road Information Program (TRIP), American Trucking Associations, American Road and Transportation Builders Association, AAA Foundation for Highway Safety, and such state "good roads" groups as the Transportation Development Association of Wisconsin. Finland and Norway among other countries, have conducted studies of the impact of winter maintenance. Road weather research is coordinated by the Aurora Project. Podcast stories about winter maintenance are an excellent learning tool.  The Federal Highway Administration gathers data in its Highway Safety Information System and promotes training through its National Highway Institute (see the NHI Road Weather Management Course) and coordinates a series of state Local Technology Assistance Programs (LTAPs) often provide useful information on snow removal and ice control; check out those from Colorado, New Hampshire, South Dakota or Wisconsin.  The University of Iowa offers a degree course in Winter Highway Maintenance.  Iowa has had great success pre-wetting salt with salt (sodium chloride) brine. The Federal Highway Administration is promoting the concept of anti-icing, an application for North America which was developed by the Strategic Highway Research Program; it has been used for many years in Europe.  Iowa DOT's program is especially advanced.  There's lots of research going on and the Wisconsin DOT has a good online library.  So do some universities like Northwestern University.   Some salt spreader and plow manufacturers (e.g. Dickey-John, Henderson Manufacturing, Epoke, Flink, Fisher) and even dealers like Monroe Truck Equipment have Websites with additional information; as do manufacturers of other snow and ice-related equipment (e.g. Didactics). So do salt storage building manufacturers Advanced Storage Technology, Dome Corp. of North America, Cover-All Building Systems, Bulk-Store Structures and Sprung Instant Structures.   And makers of brine-making equipment for use in anti-icing, including VariTech Industries, Reed Systems, Mountain Products, and Norwesco or visit distributors like Dultmeier Sales for a variety of such equipment.  Among North American salt producers, Cargilll Deicing Technology and North American Salt maintain websites with information about its deicing product lines as does Salt Union in the U.K; and the British Salt Manufacturers Association has a trove of valuable information on highway deicing. Other North American producers can provide information about deicing salt.  Winter maintenance contractors have organized the Snow and Ice Management Association and private winter maintenance service contractor VMS, Inc. has its own site.  For some online discussion, try Plowsite.com.  Note our disclaimer.

If you'd like salt-related information delivered automatically via a newsreader, you can subscribe to our Salt Institute NewsCentral service or add any of our feeds to your newsreader.  The RSS feeds for Salt and Winter Roadway Safety: For Highway Users, Salt and Winter Highway Safety: For Roadway Maintainers (Snowfighters) and the related Salt and the Environment are also available via your Web browser.

[About Salt Institute] [About salt] [About the salt industry] [News] [SI Member Business (password required] [E-Mail Salt Institute]

Search web site: