Oil and sand are applied to roads for two very different reasons depending on the season. In warm months, crews spray liquid asphalt (the “oil”) and spread crushed stone or coarse sand (the “chips”) to resurface and protect aging pavement. In winter, sand is scattered on icy or snow-packed roads to give tires something to grip. Both practices are common across the U.S. and Canada, and understanding what’s happening can save you some frustration the next time you hit a freshly treated stretch of highway.
Chip Sealing: The Summer Treatment
The most common reason you’ll see oil and sand on a road is a maintenance technique called chip sealing. A distributor truck sprays the pavement with a layer of liquid asphalt emulsion, a sticky, oil-based binder that acts like glue. Immediately behind it, a self-propelled spreader lays down a uniform coat of small crushed stone or coarse aggregate, often called “chips.” Heavy rubber-tired rollers follow right away, pressing the stone into the fresh binder so it sticks and stays put.
The result is a new wearing surface that costs a fraction of full repaving. Counties and state departments of transportation use chip seals on roads that are structurally sound but showing surface wear, cracking, or oxidation. The treatment seals the pavement so tightly that water essentially cannot penetrate it, which prevents moisture from reaching the road’s base layers and causing potholes. It also blocks oxygen from breaking down the existing asphalt underneath, slowing the aging process that makes roads brittle and cracked over time.
A single chip seal can extend a road’s useful life by several years, which is why you see it so often on rural highways and county roads where budgets are tight.
Why Sand Alone Goes Down in Winter
Winter sanding is a completely separate practice. When roads are coated in ice or packed snow, crews spread sand (or fine crusite) directly onto the surface to restore traction. The physics are straightforward: when a tire rolls over loose sand particles sitting on ice, the sand grains dig into the ice surface through a plowing action. This replaces the dangerously slick rubber-on-ice contact with a much grippier sand-on-ice contact.
Research on tire friction shows that sand maintains a relatively stable friction level on ice across a wide range of temperatures, from well below zero to the melting point. That consistency is important because rubber tires on bare ice lose grip unpredictably, especially near freezing when a thin water film forms on the surface. Sand is also less affected by loose snow blowing across the road, which can bury salt but still allows sand particles to function.
Sand is often preferred over salt in extremely cold conditions (roughly below 15°F or -10°C) because salt becomes far less effective at melting ice at those temperatures. In those situations, adding friction with sand is more practical than trying to melt the ice chemically.
How Oil and Sand Stabilize Unpaved Roads
On gravel or dirt roads, oil and sand serve yet another purpose: dust control and surface stabilization. Crews mix a bitumen emulsion into the top layer of an unpaved road and compact it. The binder coats each grain of sand and gravel, cementing them together into a flexible, water-resistant layer. As binder content increases and fully envelops the mineral grains, the layer grows stronger because the thicker film of binder reduces friction between particles and locks them in place. The result is a surface that resists washboarding, dust, and erosion far better than loose gravel alone.
What to Do When You Hit Fresh Chip Seal
If you’ve ever driven through a fresh oil-and-chip zone, you know it can feel chaotic: loose rocks pinging off your car, a sticky black surface, and orange signs everywhere. That period matters. Mohave County, like most road agencies, posts temporary speed limits of 25 mph on freshly sealed roads. Driving slowly, avoiding sharp turns, and not braking hard all help the chips settle into the binder properly during the cure period. Loose stones that haven’t yet bonded can fly up and crack windshields or chip paint on passing vehicles, which is exactly why the speed limit drops so dramatically.
Once the road has cured and crews sweep away the excess loose stone, the surface becomes durable and surprisingly quiet. That first week of inconvenience buys years of protection for the road underneath.
Environmental Tradeoffs
Neither practice is without environmental cost. Sand applied to winter roads accumulates in gutters and ditches, and spring runoff carries it into streams and lakes where the sediment can smother fish habitat and degrade water quality. Heavy metals, residual oils, and other contaminants picked up from road traffic hitch a ride with that sediment. Road agencies typically manage this with erosion and sediment control plans, including catch basins, silt fences, and scheduled street sweeping to recover as much sand as possible before it washes away.
Chip seal emulsions are engineered to cure and bind to the road surface, so once set, they don’t leach significantly. The greater risk comes during application, when uncured emulsion could run off in a sudden rainstorm. That’s one reason chip sealing is done in dry, warm weather with careful timing.