Sand versus salt — difficult decisions
There has been much discussion on whether to use sand and other abrasives or salt to treat slippery roads during winter. This is not an easy decision to make. There are pluses and minuses for both. More recently there is significant opposition to salt, but sand and abrasives also have a negative impact on the environment.
When a highway department considers just how to treat snow and ice on their roads, there are many variables to consider. Some of these include:
¯ Pavement temperature counts more than air temperature, but both are factors.
¯ Cold spots — areas of higher elevation or shaded areas create cold spots which normally require more salt or abrasives.
¯ Intensity of the precipitation — the harder the snowfall, the more chemicals needed to prevent bonding before the next treatment.
¯ Geometrics — steep grades, curves, bridge decks, etc., influence application rates.
¯ Corridors — certain roads are key to functioning of the system.
¯ Time of season — more chemicals are required in January than in March because of colder pavement temperatures and less heating from the sun.
¯ Wind conditions, causing drifting.
¯ Type of snow or ice — the wetter the precipitation, the more chemical dilution occurs, which requires more chemicals to keep the freezing point reduced.
¯ Traffic volumes — higher traffic volumes result in mixing action along with heat from friction. They are also an indication of more important roads.
¯ Rush hour — school bus traffic and importance on rural roads.
¯ Cycle time of the snow and ice control equipment is also important. Fewer trucks requires longer cycle times and more chemicals to keep the same level of service.
¯ Level of service — All of these items play into the concept of level of service. What is the condition during and after the storm? How quickly should the road be bare (or should it be bare at all)?
Now, should we use abrasives or salt? Some of the advantages of abrasives include low initial cost, immediate friction improvement, and suitability for low temperature and for use on unpaved roads.
Some disadvantages of using an abrasives priority policy include little if any ice melting ability, the benefit is only temporary, sanded roads are less safe than bare pavement, overall they are more costly than salt (more on this next week), buildup and drainage problems, it contains enough salt to generate environmental and corrosion concerns, it pits windshields and paint on vehicles, creates a skidding hazard on bare pavement after a thaw, siltation of waterways, smothering of roadside vegetation, and air quality problems. The siltation, gradual buildup of materials on the stream or river bottom in waterways by abrasives, is of greater concern to aquatic biologists than salt. Abrasives are degraded by traffic, and very fine particles get into the air, causing significant air quality problems.
Abrasives do not retain their effectiveness long. Displacement by traffic or incorporation into forming snowpack quickly diminishes the benefit. Consequently, frequent reapplication is necessary.
Next week’s article will discuss cost factors of using abrasives versus salt.
Credit for much of the information in this article and in next week’s goes to Cornell Local Roads Program, a great source of expertise available to highway superintendents statewide.