With winter conditions already upon us, snow and ice control on our streets and highways becomes a priority for highway crews. Decades ago, roads were seldom plowed until morning and almost never sanded or salted. Today, however, with our very mobile society, we expect bare roads throughout the winter. Proper control of ice and snow has become very sophisticated and indeed, more scientific.
However, it should be recognized that it is not possible to provide a "bare" or "wet" pavement surface all of the time. The characteristics of weather events and finite available resources preclude this possibility. The interactive effects of pavement temperature, air temperature, storm intensity, and timing of initial treatment, operational cycle time, traffic volume, wind velocity, and solar energy all have profound influence on the effectiveness of snow and ice control measures.
The goal of the state Department of Transportation is as follows: to provide highways that are passable and reasonably safe for vehicular traffic as much of the time as possible within the limitations imposed by weather conditions and the availability of equipment, material and personnel. It is recognized that due to resource limitations and weather conditions, pavement surfaces will be snow covered and/or slippery some of the time. The traveling public must exercise caution and drive appropriately in those situations.
The question is how best to accomplish this goal. This includes the decision to use sand versus salt. Many citizens, not familiar with the scientific rationale for this decision, prefer the use of sand. They generally believe that this is better for the environment and is less costly than salt. However, this is not necessarily the case. Read on.
There are a large number of chemicals and other treatments that are used for ice control. The DOT generally uses six -?salt (Sodium Chloride or Rock Salt), Treated Salt, Calcium Chloride, Magnesium Chloride, Magnesium Chloride with Organic Based Performance Enhancer and Abrasives (Sand). Salt is the most common and least expensive ice control chemical. Salt's ability to melt ice or form brine is highly temperature dependent.
Salt can be pre-treated or pre-wet with a variety of liquids to improve its performance. Calcium chloride and magnesium chloride are normally used for this purpose. Pre-treated salt will start to work quicker than untreated salt, will continue to perform at lower pavement temperatures, and can generally be applied at a lower application rate.
Abrasives may be natural sand, manufactured sand, or iron ore tailings. They provide immediate temporary improvement in the frictional characteristics of the pavement surface but have little ability to melt the snow or ice pack. Also, more frequent reapplication is necessary. Sand piles are usually mixed with 5 to 10 percent salt to prevent the sand pile from freezing. While abrasives have a low initial cost, the cost per application is about the same as salt once the increased application rate, salt mixed in the stockpile and mixing costs are considered. The addition of greater fuel costs, more wear and tear on the vehicles, and after season clean-up costs can dramatically increase the total cost of this product to where sand is actually more costly than salt to keep our roads safer. Areas adjacent to certain bodies of water and certain aquatic creatures can also be adversely affected by the use of abrasives.
Application rates vary according to various factors, but standard accepted rates are in the 150 to 200 pounds per lane mile for salt and salt with calcium or magnesium chloride, and in the range of 750 pounds or more per lane mile for abrasives such as sand. At these accepted application rates, one truck load of salt will be able to cover more than four times the miles that a truck load of sand will cover. That means spreading sand will take over four times as much fuel and wear and tear on the vehicles as the spreading of salt would. And, when you consider that the sand is mixed with salt, spreading sand will also spread close to half as much salt as spreading pure salt would. You're going to get salt no matter what.
There are other considerations as well. Consider the cost of stock-piling the sand in the fall and the considerable costs of clean-up in the spring. Also, the abrasiveness of sand wears off the pavement markings and generally collects in the center of the roadway, obstructing the centerline. Of interest, the villages of Dexter and Brownville near Watertown have been using only salt in their villages for the past 10 years. Their reasoning behind this decision is to save money, primarily in the costs of spring clean-up.
No matter how we clear our roads from snow and ice, there will be adverse environmental affects that's part of the price we pay for safer winter driving.
For more articles on traffic law and safety, go to the traffic safety board's website at www.franklincony.org and click on "Traffic Safety Board" under departments then look for Did You Know articles under "services". You can now "Like" Franklin County Traffic Safety Board on Facebook as well.