Ever wondered why people salt roads during the winter? 

Are you among the ones who live in that part of the world where it snows during winter? If not, then you must have visited places where it snows, right? Say for instance, Gulmarg during December. The idea itself is thrilling, isn’t it? But people who are native to that region will tell you that it’s not always hunky dory. At times, the snow really makes life difficult, to the point when life comes to a standstill.  

Guess what comes to the rescue then! A salt truck, or salt, to be more precise. You must be wondering what has salt got to do with snow. It turns out, salt helps speed up the melting of snow. Maybe that’s why one can often find salt trucks parked in places, when there’s a forecast of snowfall. In fact, drivers of such trucks spread salts on the road. The locals also help out by sprinkling salt on their sidewalks and driveways, prior to potential snowfall.  

The art of salting snowy roads 
Hilly roads can turn dangerous during winter, as they become slippery due to constant snowfall. Turns out, this is exactly why people salt roads during winter, especially where there’s a forecast of heavy snowfall. Simply put, salt prevents snow from forming on the pavement, in turn keeping the roads clear and safe. However, if you look closely, you will see that the salt spread on roads is either grey or brown. This is because, unlike your table salt, the salt here isn’t purified. Now comes the more interesting part. Why does salt melt snow? Well, the process is a bit more complicated than you can imagine. In fact, it has something to do with a scientific process called freezing point depression. 

What exactly is freezing point depression? 
As we all know from science books that liquid water freezes and turns into ice at 0°C. This is what is regarded as the freezing point. Now, here comes something fun and interesting. When salt is added to this water, it gets harder and slower for the water molecules to freeze. So, instead of freezing at 0°C, this saline water shifts the freezing point to -9.4°C, that is, the freezing point gets lowered. Okay, so what does this imply? When snow hits the ground surface already treated with salt, the area would only freeze if the temperature outside dropped further.  

This concept works best when salt is already blended with water from beforehand. Maybe this is why, people nowadays have slowly been shifting to brine solution (made up of water, sodium chloride and magnesium chloride) instead of rock salt. At times, even sand is said to do the trick! Interestingly, this process is also often called anti-icing or pre-wetting. So, now you can understand how cheap and effective salting is to ensure road safety during cold weather.