Winter Traction – Why Small Rocks, Instead of Sand

Home owners can treat icy sidewalks with sand, but on a slippery highway, whipping winds and passing trucks can blow away light material within minutes.

Instead, when there’s a need for extra traction, our maintenance contractors often rely on a carefully prepared mixture of gravel and crushed stone. The industry term for it is “winter abrasive.” The particles in this mix need to be heavy enough to stay on the road in a wind, large enough not to vanish under new snow or freezing rain, and yet small enough to keep the frustrating windshield chips and paint dings to a minimum.

The right balance between too light and too heavy depends on the type of highway. On main provincial highways, no piece of winter abrasive is allowed to be over 9.5 mm in diameter. That’s smaller than a Cheerio. Very little of the mix is allowed to be even that big, with most of the material falling between 2.36 mm and 4.35 mm in size. (Less-travelled paved highways use a larger mix with a maximum diameter of 12.5 mm.)

How do our contractors make sure that they’re meeting these standards? Many filter their supply of gravel and stone by running it through a series of increasingly fine screens. Others use crushers that grind the material down to the proper size.

Now, you may be saying, this is fine, but what about the time a whopper of a rock cracked my windshield? That was no Cheerio! This has happened to us too, and it can be annoyance or a shock. However, screened winter abrasives aren’t the only rocks on the road. Rocks get washed from the roadside onto the highway, fall from trucks, or get knocked onto the highway by wheels grazing unpaved shoulders.

Your best protection is to keep your distance from other drivers, and if you do get a windshield chip, have it fixed right away.

Did you know?

  • If a rock strikes your windshield, the potential damage has more to do with the rock’s impact velocity than its size. An increase in impact velocity from 80 km/h to 110 km/h will almost double the impact energy and the probability of windshield damage. So to protect your vehicle: slow down and keep your distance!
  • On flat, straight highway sections, maintenance trucks may briefly stop applying abrasives to avoid spraying vehicles passing in the other direction. However, they can’t do this on hills and corners — these crucial areas must be treated.
  • Maintenance crews sometimes wet winter abrasives with a liquid brine to help it penetrate compact ice and stick to the road.


  • Avoid passing a truck applying winter abrasives if you can. Staying back will protect your vehicle from flying winter abrasive, and you’ll be safer driving on the treated road. If you do need to pass, patience will pay off. Our contractors regularly pull over to let traffic pass when it’s safe to do so.

Join the discussion

Leave a Comment