So how exactly does it help to put brine and sand on icy roads?

When ice slicks over the roads and makes driving dangerous (or impossible), the state dispatches fleets of trucks designed to fight the freeze.

Brine trucks carrying salty water are dispatched to spray the roads, and dump trucks full of sand arrive at bridges and major roads to dump earth on bridges and major roads and intersections.

You may know that salt and sand is the go-to for when the roads get treacherous, but what does it actually do to make roads safer?

The simplest answer is that salt actually lowers the melting point of water. When water changes phase and becomes solid ice, its molecules become much more orderly and fixed.

“Any impurity disrupts water molecules’ ability to find each other and to organize in the right way,” said Joel Thornton, professor of atmospheric sciences at University of Washington in Seattle, told PBS. “When you add salt to the road, what you’re doing is you’re adding impurities to the water so you disrupt the water’s ability to form ice.”

Encyclopedia Britannica describes it this way: When you add salt to ice, it makes it harder for those water molecules to bond together and create the rigid structure of the ice. That, effectively, lowers the freezing point as the salt dissolves in the water and those ions snag and block and generally annoy the bonds that make ice, well, ice.

Icy roads still have a thin layer of water above the ice that is constantly melting and freezing. Adding salt lowers the freezing point of that surface water, so it continues to melt instead of freezing - leading to less ice on the roads.

If it’s too cold - say around 15 degrees or colder - adding salt isn’t going to do much, as the ice is just too compact and frozen. But at around or slightly below freezing , it can be very effective.

Both rock salt (which you can buy in big bags to use around your home) and salty brine work pretty much the same way, but brine is becoming more common because it is easier to transport and apply, starts working more quickly over a wide area and is less likely to just get bumped off the road into the dirt where it does no good.

Sand does not help melt ice. Unlike salt, it does not dissolve in the water and interfere with the way ice forms.

Instead, dirt and sand is usually placed on roads to give cars and trucks a little bit more traction while driving over it.

Imagine there is a small patch of ice on the ground, and you need to walk over it. If you dump a few shovelfuls of dirt over the ice patch, it becomes buried, and you can walk right over it.

Road crews don’t drop enough sand to completely cover the ice, but they put enough to give your car a little bit more traction that could give you enough of an edge to not slip and slide all over the road.

Sand is valuable because it can be put down to make an area navigable almost immediately, and it can stay that way for awhile, and when combined with salt, it can create a one-two punch that keeps roads a little safer.

Still, especially in the South where most people are not used to driving in winter weather, officials tend to say the best thing to do is not to put your fate in the hands of salt and sand - stay home if you can, and wait for the sun.

This story was originally published January 17, 2018 at 3:11 PM with the headline "So how exactly does it help to put brine and sand on icy roads?."