Over 30% of American roads remain unpaved, mostly in rural areas.1 One major reason is cost: paving a two-lane road averages $2 to $3 million per mile, far more than constructing an unpaved road. The tradeoff is that unpaved roads require near constant repairs to keep the surface safe for the millions of people who rely on them every day.
At Substrata, we’ve specialized in unpaved road stabilization since 1972 and helped hundreds of rural communities transform their roads. Today, we’ll look at solutions to the most common maintenance problems unpaved roads face:
An unpaved road may feel hard, but soil is relatively soft compared to other roadbuilding materials. We ran r-value tests to check the strength of soil and Type II aggregate, a common subbase for paved roads. The aggregate was over four times stronger.
Since soil is softer, it’s more susceptible to shifting and erosion such as ruts, potholes, and washboarding. These surface problems increase travel times, damage vehicles, and result in accidents. To fix them, it's crucial to know what’s causing erosion.
Erosion can develop for numerous reasons. Rain washes away soil and gravel. Traffic degrades soil, especially heavy vehicles or speed changes that increase friction. And improper construction—like omitting sloped shoulders or crowns—can make surfaces wear poorly over time. Typically, erosion stems from multiple factors.
Bethel Road was gravel. It ran downhill, turned, then followed a creek along flat ground. Drivers had to slow down to turn or speed up to climb the hill, so with these speed changes, the road began to washboard.
Heavy rain washed out the road, creating gullies two feet deep and washing the gravel into the ditch. When the creek flooded, it swept loose gravel off the low stretch of road, too. The road became impassable. Residents couldn't leave their homes, and the school bus couldn’t pick up their children.
The county graded Bethel Road, but the grader operator went too fast. The blade duck-walked, leaving the surface uneven. So, the cycle continued with each passing car and rainstorm until the county gave up and paved the road.
Paving does cut down on erosion, but it’s cost-prohibitive for most projects. After all, there’s a reason unpaved roads are unpaved! So, how can you rehabilitate unpaved roads? Assess the damage, noting the worst and most dangerous areas. You’ll want to fix these first to protect your community.
Fill potholes and grade uneven surfaces to smooth the road. For dirt roads, you can add a gravel topcoat for strength. Choose appropriately sized aggregate: too large creates a rough driving surface, while loose gravel that’s too small will wash away or work into the soil.
You may also need to reshape the road’s crown or shoulders to improve drainage (more on that soon). Reshaping costs more and takes longer than grading, but it can fix structural problems to save you time and money long-term.
Dust forms when hot, low-humidity weather dries out soil particles. Wind and passing traffic then blow this dust into the atmosphere. Wind can blow dust up to three miles high and more than 5,000 miles across the world.2
Soil type, road type, and human activity can worsen road dust problems. For example, clay soils are dustier than soils with larger, heavier particles. Road gravel can be dusty when it arrives from the quarry or become dusty as traffic pulverizes it. Industries like mining and farming also produce dust that can settle on roads; one study found that 76% of field dust travels over 600 feet before settling.3
Since environmental dust will always exist, your unpaved road will always have some dust. That’s okay. But too much dust is a problem. It scratches paint and glass, lowers visibility, and causes wrecks and respiratory illnesses. It can even kill plants by coating their leaves so they can’t absorb sunlight. And if there’s a solar farm near your roads? Excess dust that settles on solar panels reduces their efficiency and may cause fires.
Since permanently suppressing 100% of environmental dust is impossible, focus on what you can control: road dust. Check out these common dust suppressants.
Water is natural and safe to use in sensitive environments. The downsides? You have to reapply it daily—sometimes multiple times—which gets expensive. And in dry regions, watering roads can be wasteful.
Chlorides are a common chemical dust suppressant. Magnesium chloride and calcium chloride are road salts that pull humidity from the air to weigh down dust so it won’t fly up. They work well in humid climates. And the initial application is cheaper than many other soil stabilizers.
However, chlorides don’t work well in dry climates (no humidity = no moisture for chlorides to pull into the soil). They require multiple reapplications each year, making them more expensive long-term than other solutions. Finally, they corrode metal and pollute soil and water. So, chlorides have begun falling out of favor.
Oil is an old-school dust suppressant that some organizations spray on unpaved roads. Bitumen emulsions are another option that mixes water with tiny bits of asphalt. These methods tamp down dust, even in dry climates.
Petroleum products are hard on the environment. Consider this: most states have made it illegal to dump used motor oil on the ground because it poisons wildlife, pollutes water, and renders soil infertile. It just takes one rainstorm to wash oil off roads and into waterways and fields. If it’s bad for your neighbor Joe Bob to dump a few quarts of oil in his driveway, then spraying hundreds of gallons onto unpaved roads is worse.
Organic, non-toxic dust suppressants are safer and eco-friendlier than traditional ones. They include everything from vegetable proteins to lignosulfonates (a sap-like byproduct of the wood pulp industry) to the enzyme-based dust suppressant Surfa-Zyme.
The exact pros and cons of natural dust suppressants vary based on which product you choose. Overall, the biggest benefit is that they’re safe for crews and the environment; the biggest pitfall is that most require frequent reapplications, racking up costs over time.
Perma-Zyme is an enzyme soil stabilizer that binds soil particles together, helping prevent loose dust from entering the atmosphere. While it was originally designed as a road hardener, its dust suppressant qualities can last for up to two years with no other treatments.
Application costs more than some other dust suppressants upfront, but it’s cheaper than traditional soil stabilizers like polymers, cement, or lime. Perma-Zyme's long-lasting results save you thousands of dollars on maintenance. You also get the benefit of soil stabilization alongside dust control.
Muddy or flooded unpaved roads are signs of drainage issues. Since dirt absorbs water and gravel filters it, you’d think unpaved roads would naturally drain well. However, that isn’t always the case.
Some roads drain poorly because of environmental factors, such as nearby bodies of water or low-lying, swampy areas where the soil is already saturated. Construction also plays a role. Roadbuilders heavily compact unpaved roads, so most water runs off the surface, taking gravel and dirt with it. Design flaws—such as insufficient or non-existent drainage ditches and failure to adequately account for rainfall or elevation—can make roads retain water.
Poor drainage causes erosion and gravel loss that you must pay to repair. Lost material then clogs drainage ditches and waterways, making roads more likely to flood and harming aquatic life. In severe cases, mud and flooding can make roads impassable—a life-threatening situation. Roads must always remain clear so first responders can reach people during emergencies.
Unpaved roads are made of dirt, so they’ll always be a little muddy after rainstorms, especially with high-clay soil that absorbs a lot of water. However, you can greatly improve drainage.
First, add ditches to remove water. You can even partner with local farmers, building ditches to irrigate nearby fields. Clear ditches and drains of brush, debris, and snow so water can flow away from the road.
Install culverts under the road to remove water and reduce erosion. As a bonus, slightly exposed pipes double as speed bumps. (Make sure they can withstand the weight of traffic.) Finally, build up low-lying or flood-prone areas when possible. Even seemingly minor improvements, like a steeper crown or extra few inches of elevation, may be enough.
Drainage improvements make a big difference. From 2003 to 2013, World Bank Group helped construct 2,100 culverts on rural feeder roads in Brazil to allow reliable travel from rural areas to towns during the rainy season. On average, these projects decreased travel times by 13-15 minutes—helping more people find jobs, earn higher incomes, send their children to school safely, buy cars, and shop and socialize more often.4
The spring thaw is the busiest maintenance season for many communities. But these spring road problems start long before the thaw; they start with the first freeze. When water freezes in the ground, it expands and shifts the soil. Then the ice melts, and the soil collapses—resulting in potholes, cracks, and frost heaves.
Extremely cold temperatures cause soil to freeze deeper, while multiple freeze-thaw cycles in one season compound the damage. Weather-related maintenance can also worsen conditions, such as when snowplow blades accidentally dig into the soil.
In cold climates, unpaved road stabilization is cheaper and easier before the freeze. You can implement the drainage solutions we discussed earlier; the better roads drain, the less water will freeze in them. Applying a soil stabilizer that can last all winter will also save your roads. (See how it worked for this county.)
Perform regular spot maintenance during cold months to keep problems from getting out of hand. Proper snowplowing techniques also help: travel at low to medium speeds, with the blade slightly above the road so it won’t dig into the surface.
Finally, if you’re rehabilitating a road that’s already damaged from freeze-thaw cycles, use the erosion solutions from the beginning of this blog. Grade the road smooth, fill potholes, apply gravel, and reshape the surface as needed for repairs.
Some unpaved road problems aren’t on the road. Roadside safety hazards include:
Vegetation and buildings beside rural roads block visibility. Additionally, foliage lures wildlife closer to traffic, causing more accidents, vehicle damage, and injuries. Many unpaved roads lack shoulders due to geographic features or private property. (After all, you can’t just slap a road on someone’s land.) Pair that with steep embankments and no guardrails, and you’ve got some serious safety concerns.
Budget constraints commonly exacerbate roadside safety hazards, as safety features like installing guardrails, building emergency pull-offs, and trimming vegetation can be pricey.
Trimming plants is essential, so don’t scrimp here! Instead, reduce other unpaved road costs to free up resources for this vital rehabilitation. For example, you could switch to a longer-lasting dust suppressant, then apply those savings to roadside maintenance.
Traffic management is your next step—and the evidence shows that it’s effective. Unpaved U.S. roads have fewer traffic fatalities than paved roads, likely due to lower speed limits.5 A Swedish program reduced speed limits, increased sanctions for traffic violations, and installed safety cameras on rural roads. From 1997 to 2014, speed limit compliance increased 30-40%, and traffic fatalities decreased over 60%.6
Often, small adjustments are sufficient. Signage is an affordable way to warn motorists of sharp turns, deer crossings, high water, and more. Installing reflectors near turns or embankments is also a simple, cost-effective, long-lasting solution.
Speaking of solutions, we have one last tip: choose an unpaved road stabilizer that solves multiple problems at once, like Perma-Zyme.
As we mentioned, Perma-Zyme is an enzymatic soil stabilizer that treats roads to create a hard, concrete-like surface that resists water and erosion. It can even lock in a gravel topcoat to prevent loose material from washing away and to strengthen the road. This significantly reduces problems like:
Perma-Zyme treated roads last for 10+ years with little to no maintenance. With yearly maintenance costs as low as $0 for over a decade, you’ll save tens of thousands of dollars and free up your crews to work on other essential projects.
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