The Physics of Salting Roads

Winter is a harsh season here in Colgate and usually, it snows heavily and makes it hard to walk or drive on the road. The recent snow up to now has not caused large congestion on the road because there are almost no snow or ice on the road. It is because a certain substance is pulled onto the road and lower the freezing point of ice, and it turns out to be very safe in the winter! Usually people add saltwater and it turns out to be very useful!

According to National Snow & Ice Data Center, saltwater has a relatively lower freezing point than freshwater, which freezes at 0 degree Celsius. And for saltwater,  its freezing point decreases by 0.28 degree Celsius for every 5 ppt increase in salinity. 

The graph above shows the freezing point of salt with respect to its salinity. By adding certain portion of salt into fresh water, the freezing point continuously decreases till around -21 degree Celsius when the salinity is around 290g/kg. After this point the freezing point begins to increase as the salinity increases.