Salt On City Streets

Individuals rely on our roadway network throughout the year and safe winter driving conditions depend on the effective use of salt.

Sodium Chloride (NaCl), more commonly known as salt, is our first defence against a winter storm. Salt is spread early in a snowstorm on a priority basis to prevent slippery roadway conditions.

What does Salt do?
When salt is added to an icy surface, it will seek heat from the air and pavement, and seek humidity from the air, snow, and ice to dissolve. Once dissolved, it become a salt brine solution. The salt brine solution melts the surrounding snow and ice. The melting spreads out from that point until the ice is melted or the salt is all dissolved.

How does Salt work?
Salt acts as a freezing point depressant. This means that when salt is added to water, the freezing point of the resulting salt brine becomes considerably lower than that of pure water. This salt brine freezes at -21.1ºC. This is much lower than the well-known freezing temperature of water at 0º C.

Our Salt Usage
Whenever possible, salt is spread early in a winter weather event on a priority basis to prevent unsafe roadway conditions and improve our winter driving. Salt is applied very early in the storm in order to create a ‘brine sandwich’ effect which is a combination of snow/ice, salt and water.

When the depth of the snow makes it impractical to use salt, plows are used to remove the snow from the roadway. Abrasives, such as sand and crushed rock, are used in colder temperatures when salt is not effective, or for roads that have snow-packed treatment standards. Abrasives do not melt snow and ice. They are used to increase traction between the road and the vehicles’ tires when melting of snow and ice is not required or not possible.

Did you Know?

• Rock salt is a naturally occurring product
• Salt used on the roadway is the same as table salt
• Rock salt is endothermic – it needs heat to dissolve
• Optimal salt spreading speed is between 30 and 40 km/h
• Salt is spread in a bead on the “crown” or highest point of the roadway. As the salt brine forms, it follows a natural downhill progression and spreads across the roadway.