Calcium chloride is mixed with salt in colder temperatures to increase the salt's melting ability. Direct sunlight and traffic also help salt work better. Heavily traveled roads may often become more slushy and clear sooner than lesser traveled roads in rural areas. Salt was first used for snow and ice control in the 1940s, but its use didn't become widespread until the 1960s. Salt is used as the principle deicer because it is the most readily available and least expensive deicer.
Salt is non-toxic and harmless to skin and clothing.
When handled and stored properly, salt is harmless to the environment. 500 pounds of salt will release enough brine to keep snow and ice from bonding to one mile of two-lane pavement. Over 10 million tons of salt are used each year in the USA and 3 million tons in Canada. Because salt becomes substantially less effective below 20 degrees F, calcium chloride is used to improve its effectiveness in colder temperatures. The liquid calcium is sprayed onto the salt before the salt reaches the spinner on the back of the truck.