Snow and Ice Control

MaineDOT has a fleet of roughly 400 plow trucks that are used to control snow and ice on approximately 8300 lane miles of Maine’s state roads. Like most entities that maintain high-speed, high-volume highways, MaineDOT uses an anti-icing approach to snow and ice control that is very effective for returning roads to bare pavement after a storm ends. MaineDOT usually plans on an average of about 30 “treatable” events in a winter.

Snow and Ice Materials

Materials/Supplier Information

  • Rock Salt (Sodium Chloride - NaCl)
  • Winter Sand
    • A sand/salt mix made by MaineDOT using coarse, clean, sharp sand that passes through a square-meshed 1/2 inch screen, thoroughly mixed with approximately 100 to 120 pounds of salt per cubic yard.
  • Liquid Chlorides

Salt Brine Facts

  • What is salt brine?
    Salt brine is water saturated with sodium chloride, or more simply rock salt dissolved in water. It is part of MaineDOT’s anti-icing program to take a proactive approach to controlling snow and ice on Maine’s highways.
  • When is salt brine used?
    Salt brine is best used when pre-treating the road in anticipation of frost or winter storms. Salt brine can prevent frost on the road for up to three days. If applied just before a winter storm, salt brine will begin working as soon as the first snowflake falls and will delay the accumulation of snow and ice on the pavement.
  • What are some other benefits of salt brine?
    Once a winter storm is in progress, salt brine is sprayed onto the rock salt as it is applied, to accelerate the melting of snow and ice. This is known as “pre-wetting.” Pre-wetted rock salt stays on the pavement instead of bouncing off the roadway and wasting material. Pre-wetting with salt brine in this manner reduces the amount of rock salt that MaineDOT must use overall. Salt brine costs much less than other liquid chlorides – up to 10 times less per gallon!
  • Salt brine allows MaineDOT crews to be proactive and get a jump-start on the storm. This means that MaineDOT crews can treat the roads before the driving conditions decline and they can have entire routes pre-treated so that the ice and snow never has a chance to bond to the pavement. Because of this, the roads will return to bare pavement much quicker once the storm has ended.
  • How is salt brine applied to the road?
    Motorists can expect to see MaineDOT crews pre-treating the roads with salt brine using specially modified tanker trucks, trailers, or units that slide into the back of a typical plow truck. Most of this equipment is capable of spreading salt brine over one, two, or three lanes of pavement.
  • How does salt brine fit into MaineDOT's anti-icing approach?
    MaineDOT’s proactive use of salt brine is two-pronged:
    • First, salt brine is used on roads and bridges prior to a storm to delay ice and snow from sticking to the roadway.
    • Second, salt brine sprayed on rock salt is used in plowing to fight the buildup of ice and snow throughout the storm.
  • What should I do when following a vehicle applying salt brine?
    Vehicles applying salt brine usually travel at speeds of less than 40 miles per hour. Motorists should stay back at least 100 feet from the back of the vehicle.
  • When does MaineDOT use other liquid chlorides?
    The effectiveness of rock salt and salt brine decreases as the temperature drops. Therefore, as storms become colder (low 20s and below), snow fighters must use chemicals that work at lower temperatures to supplement the rock salt. Liquid calcium or magnesium chlorides are the most common options and are applied directly to the rock salt during the storm in the same manner as the salt brine is in warmer storms. Presently, MaineDOT uses a magnesium chloride blend known as Magic Minus Zero for this purpose.

Approximate use of materials by MaineDOT

About Anti-Icing

There are two approaches to snow and ice control: anti-icing and de-icing. De-icing is the approach with which most people are familiar because it has been around longer and it is the approach that is most likely to be used on lower-speed local roads.  De-icing is characterized by allowing the snow to accumulate until there is enough to plow, and then, when it is plowed, a large amount of a sand and salt mixture is spread to provide traction. This process is repeated as necessary throughout a storm.  While this approach can be generally effective on the lower-speed, lower-volume roads, it will often result in "snow pack"- snow and ice that is bonded onto the road surface. Snow pack can often last for many hours, and sometimes days, after the end of a storm event, and crews can spend many hours of overtime and large quantities of salt to remove it.

Under an anti-icing approach, snow fighters today use carefully calibrated equipment to spread a measured amount of salt early in a storm, and as necessary throughout, to prevent the snow and ice from bonding to the road. Salt is not applied every time the road is plowed.  Because the snow and ice are prevented from bonding to the pavement, vehicle tires have much more contact with the pavement surface and the roads will clear much sooner after the storm ends.

This approach does require better training, equipment and technology, but it also provides a much higher level-of-service at a lower overall cost. Under either approach, roads can still become slippery from time to time during the storm events; however, anti-icing dramatically reduces the amount of time that the traveling public is exposed to icy conditions.

De-icing vs. Anti-icing Information

Plowing Priorities

Snow and ice control operations are limited by the resources available (specifically:  budget, personnel, equipment and materials). Due to these limited resources, the level of service for snow and ice control has been associated with the Department’s established highway corridor priorities. 

For each highway corridor priority, target route lengths will dictate the normal cycle times that can be expected based upon average conditions, while local geographic and/or geometric factors will dictate whether particular routes need to be longer or shorter than average.  In addition, during a winter storm event, the level of service for all routes will typically be reduced between the hours of 10:00 P.M. and 4:00 A.M, depending upon specific storm conditions. 

The following table provides an overview of the various goals associated with each corridor priority:

Additional Information

Corrosion

The chemicals used for snow and ice control are typically some form of chloride.  This includes sodium chloride (rock salt), calcium chloride, and magnesium chloride.  Chlorides are the most cost-effective way to depress the freezing point of water, which is critical for snow and ice control.  Unfortunately, chlorides are also known to accelerate corrosion on most bare metals, which is why northern states have always had to contend with corrosion issues.

Recently, there have been some claims that the corrosion issue has become worse in the last couple of years.  In addition, calcium chloride is often held up as the culprit for this perceived increase.  While we may not have all of the answers to what may be influencing these statements, we can offer the following facts and observations:

  • Rock salt is, by far, MaineDOT’s primary snow and ice material.
  • Liquid calcium or magnesium chlorides are generally used to supplement rock salt during cold storms through pre-wetting. When these types of products have been purchased by MaineDOT, we have paid approximately $0.40 more per gallon to add corrosion inhibitors that bring the corrosion rate of these products on bare steel down to almost that of distilled water.
  • When these products are used (which is not every storm or in all areas of the state), they are normally used at a rate of about 2 gallons per mile. Presently, MaineDOT uses a product known as Magic Minus Zero, which is an environmentally-friendly magnesium chloride blend. Due to performance and cost considerations, MaineDOT has not purchased liquid calcium chloride since May 2005.
  • Motor vehicle inspection laws have become stricter in recent years and licensed mechanics have indicated that corrosion that would have previously passed inspection will not pass today’s standards.
  • Automobile manufacturers have been eliminating the use of a chemical known as “hexavalent chromium.” Hexavalent chromium has been used as a corrosion resistant coating on many steel, zinc, aluminum, and magnesium motor vehicle parts, including thousands of fasteners, v-belt pulleys, brackets, levers, radiators, brake lines, body panels and wheel rims.
  • From what MaineDOT has been able to find, the following list indicates the time frame in which various auto manufacturers eliminated the use of hexavalent chromium:
    • Volvo, Opel: 1990
    • GM: 2003-2006
    • VW: 2004-2006
    • Ford: 2005
    • Toyota, Hyundai: 2006
    • Nissan, Daimler, Chrysler: 2007
  • More information on hexavalent chromium is available on the web or directly from the automobile manufacturers.
  • Reports of premature corrosion seem to be associated with certain years, makes and models of automobiles while other manufacturers seem to have very few or no issues with corrosion.
  • The manner in which a person uses their vehicle also affects how corrosion may come into play. Vehicles that are washed and used regularly throughout the winter season generally seem to have fewer issues. Vehicles that are driven only during storms and are then parked until the next storm (typically 4WD vehicles) seem to fare the worst.
Reports and Information

Salt Report from the Margaret Chase Smith Policy Center

National Cooperative Highway Research Program (NCHRP Report 577)

Additional Information