During the winter, road salt is applied to the roadway to melt snow and ice. For regions that experience frequent snowstorms, like Pennsylvania, salting can help keep streets and sidewalks clear and prevent slick driving conditions. Road salting is a common practice in many states and is widely considered effective for preventing weather-related collisions. The American Highway Users Alliance found that road salt reduces crashes by 85%.
Road salt is a large-crystal rock salt sprinkled directly onto roadways using specially equipped salt trucks. Road salt is typically either sodium chloride (the same as table salt) or calcium chloride (which is just as effective but can be cheaper than sodium chloride). Using road salt is a means of freezing point depression, which means that road salt can lower the freezing temperature of the water. When temperatures are below 32 degrees Fahrenheit, sprinkling salt directly on icy roads can melt icy patches on the roadway.
While it may be a tried-and-true method for preventing ice, road salt can take a toll on vehicle parts and the environment. So, what’s the verdict? We spoke to Dr. Sam Earman, associate professor of geology, about using salt.
Q. Is the road salt that Pennsylvania uses dangerous to the environment?
Yes, road salt can have several negative impacts. Soils near roads can have salt content high enough to harm vegetation. Another issue is the high salinity in streams and lakes. Many streams and lakes have had their salinity increase over the last few decades (and there is often a pattern with higher salinity values during the snow/ice/road salt season), and studies have shown that groundwater is affected as well. Many aquatic organisms can be sensitive to increased salinity.
Q. What happens to the road salt once it’s on the roads?
Some will end up in the soil near the road (for instance, a car drives through a puddle of salty water and some of the water sprays onto the ground). Most roads are designed with storm drains that typically discharge to a stream or lake, so a lot of the salt will end up in these waterways. Salt is also corrosive. In addition to that being a problem as far as keeping roadways and bridges in good repair, the salt that splashes onto your car can cause problems (I’ve seen estimates that corrosion from road salt is responsible for billions of dollars of car repair costs per year in the USA).
Q. Is the spray that they sometimes put down before a storm safer/less safe? And why?
It’s somewhat safer. Sometimes the pretreatment is just a salt (sodium chloride) solution, with the salt dissolved in water. There are other salts that are used in liquid form for pretreatment (solutions of calcium chloride and magnesium chloride are two common liquid pretreatments/deicers); these can have many of the same impacts as sodium chloride. However, pretreated roads typically need less salt than roads that only get deicing treatment after ice is on the roadway, so even if the same chemical (sodium chloride) is used, the impact is less because less is used.
Q. Anything else you’d like to add?
As with many things in life, road salt is a tradeoff—while there are negative impacts, it does improve road safety. Improved forecasting (so we know when salt is really needed, and can pre-treat if possible), pretreatment, and using only as much salt as needed are all things that can help. In recent years, many agencies have cut back on salt use while maintaining road safety. Although we don’t typically think of salt as being expensive, think of how much salt is needed for all the roads in PA in a year. For the winter of 2015-2016, PennDOT spent roughly $3.5 million on road salt (and that only covered roads PennDOT is responsible for, not county/municipal salt use)! So, using less salt not only benefits the environment, it saves tax dollars as well!