Road salt is the destroyer of roads, and it does not stop with roads. It destroys bridges, parking structures and any other paved surfaces to which cars and trucks carry it. That includes your driveway and the floor of your garage, if you drive on salted streets before parking your car or truck at home.
It also destroys the cars and trucks that drive through it. Road salt corrodes wheels, brakes, electrical wiring, sheet metal and more. It is particularly rough on aluminum and mild steel wherever paint and “rustproofing” fails.
When spring comes, or just a midwinter thaw with rain, it washes off the roads and vehicles. The runoff increases salinity in soils near the road, in ground water and in surface water. Farm fields near salted roads are fringed with soil that supports only “salt tolerant” plants, not crops or native plants. Lakes that have taken years of salty runoff fail to “turn over” in the spring or fall, and the lake bottoms, deprived of oxygen, become dead zones.
Sure, road salt keeps traffic moving on the day it’s applied, and makes the road safer to drive for several days following. The short-term benefit does exist. In the months and years to follow, longer-term damage shows up. Road salt degrades both the built environment and the natural environment.
Let’s be clear about what constitutes “road salt.” Sodium chloride, almost the only ingredient for table salt or sea salt, is the most common type of salt used. It may be applied to the roads as rock salt or as a very concentrated brine.
Calcium chloride and magnesium chloride are sometimes called alternatives to road salt, but chemically, they are also defined as salts.
The sodium ion in sodium chloride is particularly hard on woody plants. However, the chloride ion, which is common to all the above salts, contributes to the corrosion of concrete and reinforcing steel, no matter which salt it comes from. While sodium chloride penetrates concrete more easily, it seems that calcium and magnesium chloride corrode vehicle parts more rapidly. It is not clear that there is any overall advantage for any of the chloride salts, except that sodium chloride is cheaper by the ton.
Michigan uses about 2 million tons of road salt annually. This varies, of course, from year to year depending on the weather, but it is a reasonable round figure.
Some people look at this in purely financial terms. “USEPA estimates that every $50 ton of road salt causes approx. $750 in damage to concrete, bridges and vehicles.” (From http://www.iappo.org/pdf/IAPPO07_RoadSalt.pdf.) Xianming Shi, Ph.D. with the Western Transportation Institute at Montana State University, pegged the hidden costs of a ton of road salt at $469. Using these figures, $100 million spent on road salt in Michigan results in something like $1 billion – $1.5 billion in damages annually, and that does not count the damage to soil, water and wildlife.
I think it is clear that we should value the long-term protection of our local environment over the short-term (and short-sighted) policy of keeping traffic moving in all sorts of weather. In this case, it means working to minimize the use of road salt (whether sodium, calcium or magnesium chloride), educating legislators and the public about the long-term costs of road salt, and working toward the possibility of getting along without it altogether.
A variety of organic de-icers in liquid form are effective, and are chemically much safer for the roads and for the natural environment than salt. Most are made from agricultural by-products such as corn stalks or brewery waste. They are considerably more expensive than salt, and the amount that can be produced without growing crops especially for the purpose is limited. However, they could work with a policy of de-icing only critical intersections and bridges (no chemical corrosion to worry about) and relying on plowing and sand for the rest.
This would not keep all traffic moving at all times. The public would have to accept that there are some weather conditions in which cars and trucks are not a good means of transportation.
We could also reduce the problem by reducing traffic. In the long term, we should be building a robust public transportation system so use of private automobiles is not necessary, winter or summer. We should be building communities in which homes and workplaces and schools and shopping are mostly in walking or biking distance, communities knit together with light rail and bus routes. Heavy rail and water travel could handle much of the necessary long-distance transportation with radically greater energy efficiency than cars and trucks and planes.
Of course, that’s already our long-term program, isn’t it? If we can come close to making it a reality, then banning road salt permanently is easy.