Rational materials selection
Every winter, millions of tons of snow and ice control materials are applied to North American roadways, sodium chloride chief among them. Applauded by highway safety advocates and economic development interests who extol safe and passable winter driving, use of deicers and abrasives has been accompanied by a half-century of concern and distrust by environmental groups and citizens wondering if their tax dollars are being well-spent. Too often, it seems, the decision on which material to apply and in what amounts has been seen as more art than science – and some people just don’t like “modern art”!
This past week, the Transportation Research Board published a new set of research-based Guidelines for the Selection of Snow and Ice Control Materials to Mitigate Environmental Impacts..” (NCHRP Report 577.
Previous studies have exhaustively evaluated the effectiveness of the several deicers being used. The Salt Institute's summer 2004 issue of Salt and Highway Deicing answered the question: “Are you using the right amount of ice control chemical?” It reported results of another NCHRP study (NCHRP Report 526). Still other studies have examined the environmental impacts of salt and other deicing alternatives. None have tried to integrate the questions of material selection, application rate and environmental impact. That’s what Report 577 has done.
The Report examined 42 deicing chemicals, chief among them salt (NaCl) and compared salt with two chloride deicers (CaCl and MgCl), two acetate deicers (KA and CMA) and with abrasives, creating a decision tool to quantify costs, performance and impacts on environment and infrastructure and reach objective recommendations. Here's what the report found:
It didn’t surprise us much at the Salt Institute that the decision tool, applied to priorities of current snowfighting practice as determined by survey, gave the edge to salt. In the temperature range for most snowfall, 25° to 30°, salt (NaCl) scored 90.4 compared to second-place MgCl (71.1 to 76.4), followed by CaCl (64.8 to 76.1), KA (23.9 to 31.6) and CMA (18.2 to 19.2). Sodium chloride retains its strong preference score of 90.4 down to 15° F (at that temperature, MgCl is 83.6; CaCl, 77; KA, 35.3 and CMA, 18.6). This model, of course, reflects the current preference for cost-savings and roadway clearing performance.
The second example weighted all four variables equally, which means environment and infrastructure impacts were half the scoring. Surprise, while salt’s advantage was muted by lowering the weight of its strongest suits, its lower cost and effective performance, the results were unchanged. Salt earned the highest scores down to 15° F and the other deicers follow in rank, though more tightly bunched (e.g. at 15°, NaCl is 75; MgCl, 72.2; CaCl, 68.1; KA, 52.8; and CMA, 43.1.
The real news was the impact using a third example with “environment/infrastructure priority” weighting -- three-fourth of the score representing environmental and infrastructure impacts, a quarter for performance -- and totally ignoring cost. In this example, all four deicers are tightly clustered between 15° and 30° F. Potassium Acetate earns top honors at 63.8 to 67.4; narrowly edging out CMA at 63.5 to 63.6; NaCl is third, 62.5 at each temperature; MgCl is 59.2 to 63.1 (edging out salt below 20° F; while CaCl registers 57.2 to 61.0.
There you have it: an objective study integrating concerns of cost, performance and environmental/infrastructure impacts which shows that salt is the superior choice in most circumstances. There are times and location when other products are preferred, but in normal circumstances salt will be the best choice to keep winter roads safe and passable.