The Trouble With Road Salt — And How It Reinforces Car Dependence
Editor’s note: This article originally appeared on Strong Towns and is republished with permission.
If you live in a northern state, you may be pretty accustomed to views like the one above.
During winter storms, many northern climates use salt as a primary means of de-icing roads in the winter. Road salt is pretty inexpensive to purchase up front, but it’s actually quite damaging to our public infrastructure (roads, bridges), vehicles, and fresh water sources. Salt, or sodium chloride, is corrosive, suggesting that this inexpensive short-term fix to make our roads safer may be costing us more in the long run.
Our use of salt increased exponentially after World War II, with the rise of the suburbs. As people became reliant on cars to travel to work, driving through all weather conditions became crucial to the economy, and thus we saw salt being introduced as a major tool to control winter road slickness.
When commuters and truckers needed to travel in every condition, it became policy in many cities and towns that the roads would be cleared shortly after a storm. With more cars on the roads during slippery conditions, more collisions were prone to occur, so further solutions past a typical plow were sought out. A more recent study found that by dumping salt on our snowy and icy roads we reduce road collisions up to 87%.
But before our society revolved around the use of cars, when storms came and made roads unsafe, a majority of people simply accepted the pavement was not traversable and stayed home. If there wasn’t a way to travel by walking or by train, trips were delayed and people took the days off until plows could come through and the weather cleared. Those that needed to drive in dangerous conditions put snow chains on their cars, and local governments would spread sand and cinders to improve traction on the ice.
Although people might not have known this at the time, staying home for a few “snowed-in” days might ultimately be the better option for our towns’ financial resilience than our current habit of instantly clearing roads. Ostensibly, rock—or road—salt is inexpensive. It’s one of the reasons we rely on it so much, as the United States uses up to 20 million tons of salt per year to de-ice roads. Nevertheless, the United States Environmental Protection Agency (EPA) has estimated that using rock salt as a de-icer has cost us approximately $5 billion dollars in annual repairs to cars, trucks, roads, and bridges, because of the long-term damage it does to vehicles and infrastructure.
For those of us that live in colder northern climates, we all know that eventually after years of driving on salty roads, the bottoms of our cars will rust and erode. The chloride ions in salt have the ability to break down the protective oxide layer formed on the surface of some metals (including aluminum), and speed up the process of long-term damage. Not all pavement is created equal, but salt will shorten the lifespan of concrete and asphalt by accelerating the normal deterioration process through the freeze-thaw cycles in winter.
Even though road salt decreases the life expectancy of our infrastructure, in the Northern U.S. and Canada, it’s become a necessity to making our roads safe for driving in snowy winters. Typically, we cover our roads with halite, or rock salt (the same form of salt we sometimes use for french fries) once it’s been through a lengthy purification process.
Salt works by lowering the freezing point of water through a process called freezing point depression. Water needs to be at a temperature of 32 degrees Fahrenheit (0 degrees Celsius) to begin forming into ice. Essentially, once salt is added into the mix, water has to get a lot colder than it normally would to freeze. That’s how we get the ice-melting-effect when we sprinkle salt on our front porches.
Of course, inexpensive rock salt isn’t the perfect solution to de-icing. When temperatures drop below 20 degrees Fahrenheit, it can be too cold for sodium chloride to be effective on its own. That’s when you may see local public works and transportation departments adding other chemicals (salts) such as magnesium chloride or calcium chloride to their salt (sodium chloride) mixes.
Not only does sodium chloride contribute to the erosion of pavement and metal, once it washes away from the road, it leaches into the ground and can pollute our freshwater systems, causing a rise in sodium levels. And as of right now, we have no way to remove it. In 2018, a study of wells in Dutchess County, New York, found that the sodium concentration was much higher than the federal and state recommendations. They discovered levels as high as 860 milligrams per liter in some wells, while the general recommendation sits at 270 milligrams per liter.
Joseph Stromberg from the Smithsonian Magazine wrote, “As more and more of the U.S. becomes urbanized and suburbanized, and as a greater number of roads crisscross the landscape, the mounting piles of salt we dump on them may be getting to be a bigger problem than ever.”
Canada declared road salts as an environmental toxin in 2004, and they placed new guidelines on its use. Many local U.S. governments have searched for ways to at least reduce the use of road salts. Finding an alternative that eliminates the use of salt entirely is not so simple, though, as many of these alternatives have higher upfront costs. Other potential de-icing options that are at the same or lower price point of salt tend to not be as effective in breaking down icy roads.
Removing salt from our roads entirely may seem a daunting feat while we rely on cars for transportation, but perhaps we can reduce its use. Organizations and some local governments are focusing on spreading the right amount of salt for different conditions.
The Minnesota Pollution Control Agency, for instance, offers “Smart Salting” training to individuals and organizations. Their goal is to “provide the latest technologies, best practices and tools, and available resources to assist your organization to be effective and efficient in managing snow and ice.”
The Wisconsin Salt Wise Partnership works to educate maintenance professionals on how much salt is really needed to be effective. Even in our personal salt use, when maintaining our driveways and sidewalks, we tend to sprinkle more salt than we really need to effectively break down ice.
There’s also been discussions about pre-salting the road before a storm, a practice Rhode Island adopted in 2012 called Anti-Icing. A more obscure alternative applies beet and tomato juice as a solution to keep our roads from icing over. It may seem odd, but the use of a prickle brine is also said to help minimize salt runoff and potentially help reduce salt use.
Besides changing the way we dump salt on our roads, there are possible innovative solutions regarding the use of porous pavement. The EPA writes: “porous or permeable pavement allows standing water to seep through, removing water from roads that would normally go through freeze-thaw periods, thus preventing ice formation on the roads.”
Over the years, road salt has caused a lot of problems and damage to our infrastructure and natural environment. Changing the way we salt our roads may be a good immediate fix to help reduce the speed of corrosion, but to really save our infrastructure, we need to rethink the way we’ve built our towns and cities to revolve around the automobile. If we continue expanding our roads instead of focusing on maintaining what we’ve already got, it will only create more demand for de-icing measures. In other words, if we want to stop literally salting our own earth, then we must get away from our dependence on cars.