Reducing the Traffic

Vehicles traveling on unpaved roads stir up dust. Reducing the number of vehicles can reduce dust. Traffic can be reduced voluntarily; encouraging walking is one way. Traffic can be reduced by restricting vehicle weight or type, or by limiting motor vehicle access to dirt roads. For example, the City of Kotzebue prohibits anyone under 14 years old from using a snow machine or all-terrain vehicle unless with an adult on the same machine.

Reducing the Speed

Fast moving vehicles stir up dust. Studies show that PM10, or dust, goes up with vehicle speed. Reducing speed from 40 miles per hour (mph) to 20 mph reduces dust emissions by 65%. Speed limit signs and enforcement can reduce speeds. Drainage channels across roads and speed bumps can reduce speeds. The effectiveness of speed limits depends on law enforcement and community willingness to abide by the rules. Speed bumps and drainage will only reduce dust close by.Improving Road Design

Good road drainage can reduce dust. If a road surface has poor drainage, puddles will form. Water floats the fine particles (fines) up from the soil beneath the road. With traffic, water and wind spreads the fines as mud or dust. Standing water next to a road may saturate the roadbed, resulting in potholes. When the fines are washed away, or blown away, the larger particles are left unanchored. These larger particles are pushed to the side of the road, resulting in a need for expensive road resurfacing. If a road is treated with a dust palliative, the performance of the palliative depends on the road shedding water and having a smooth driving surface.

For more information on road design, see: Road Design Resources (PDF)

Water the Road (Palliative 1)

Moisture in the surface of dirt roads causes particles to stick together. The moisture content of dirt roads can be increased by watering the road surface. Depending on weather conditions, a single watering may be effective for hours or for days. Though water is available in almost all Alaskan communities, moving and spreading it on unpaved roads can be a problem for smaller communities. Larger communities may have water trucks to take advantage of local water supplies. When water is applied alone, it provides a short- term reduction in dust. Regular, light watering is better than less frequent, heavy watering.

Several kinds of equipment are being developed for spreading water from a trailer behind a 4-wheeler or from the back of a pickup truck. These systems are designed for shipping to rural communities, and for easy maintenance.

For more information on road watering, see: Dust Palliatives and Road Watering History (PDF)

Covering Unpaved Road Surface Soils With Gravel

Applying gravel to a dirt road surface can reduce dust. Gravel provides a hard surface protecting soils from vehicle wheels. Local road maintenance specialists or ADOT contacts can provide information about effective ways of gravelling roads. Gravel does not reduce the strength of air currents caused by vehicles themselves, so traffic can still blow loose soil particles into the air. Without a good road base of crushed aggregate, traffic will push surface gravel down into the ground, especially when the road is wet. If the road surface does not have enough fine material to cement the surface gravel in place, traffic will push the gravel away from the driving lanes.

To be effective over a long period of time, new gravel must be anchored to the road surface. This is done through incorporating gravel with aggregate mixes or soil adhesives. If gravel is lost by being pressed into soils beneath the road, then the use of geotextile fabrics may be necessary. These fabrics are constructed of polymer threads with very high tensile strength, and are available in designs that either form water barriers or allow water, but not fine soil, to migrate through.

Increasing Moisture Content of the Road Surface (Palliative 2)

Moisture in the surface of dirt roads causes particles to stick together. The moisture content of dirt roads can be increased either through spreading water or by application of deliquescent salts which attract water. Deliquescent salts are one kind of dust palliative. A deliquescent salt, like calcium chloride or magnesium chloride, absorbs water from the air. Soils treated with these salts have a higher water content than untreated soils. Slippery wet roads and vehicle corrosion are disadvantages of salt application. Also, rainfall eventually removes salts from the roadway. The practical duration of a salt application is no more than one or a few years. Calcium chloride has been tested and used as a dust control palliative in Alaska in many places over several years.

For more information on using dust palliatives, see: Prepare the Road for Palliatives (PDF) and Dust Palliatives

Binding Particles Together (Palliative 3)

Another kind of dust palliatives includes chemicals which bind fine particles together or onto larger particles. These chemicals fall into several groups, such as petroleum-based, organic nonpetroleum, electrochemical stabilizers, and synthetic polymers.

Petroleum-based Binders include emulsified asphalts, cutback asphalt, and Bunker C. These agents coat particles with a thin layer of asphalt increasing particle mass and decreasing the chance of becoming airborne. Emulsified asphalt is a mix of asphalt and water which penetrates road surface dirt. This works well when the asphalt is mixed into the top inch or two of road surface with a grader. These products can contaminate waterways due to runoff and are generally not considered anymore.

Organic Nonpetroleum Dust Suppressants include lignosulfonates, and resins. Lignosulfonates result from the manufacture of paper when lignin is extracted from wood. Lignin is a natural polymer and can bind soil particles together. Lignosulfonates are water soluble and can move out of, or deeper into, a roadway surface with rainfall. These products corrode aluminum unless calcium carbonate is present. Lignosulfonates work best with fine dusts having a high plasticity in dry environments, such as clay particles. Glacial tills, common in Alaska, have low plasticity. Lignosulfonates may be of limited value in controlling dust in Alaska.

Electrochemical Stabilizers include sulphonated petroleum, ionic stabilizers, and bentonite. These products neutralize soils that attract water and allow bonds to form between particles. Electrochemical stabilizers need to be worked into the road surface, requiring equipment that may not be available in remote rural communities.

Synthetic Polymer Products include polyvinyl acrylics and acetates. They bind soil particles and form a semi-rigid film on the road. These products are either liquids or powders that are mixed with water. Products are applied in liquid form and require drying. Temperatures during the curing should remain above freezing. Traffic should be diverted from treated areas until drying which can take 12 to 24 hours. Synthetic polymer products have been used for dust control and improved soil strength on a number of airfields in Northern Canada and Alaska.

For more information on using dust palliatives, see: Prepare the Road for Palliatives (PDF) and Dust Palliatives

Sealing Unpaved Roads with Pavement or Other Impermeable Materials

Paving is the most effective, and most expensive, method to control dust from unpaved roads. Asphalt and Portland concrete provide durable and effective surfaces that prevent the breakdown of soil surfaces. Paving is very expensive. In the past few years, roads in Kotzebue carrying more than 500 vehicles per day have been paved. Thin pavements, like chip seals, have been applied to roads in southern Alaska but can fall apart during breakup. Paved roads may still accumulate dust as vehicles enter from unpaved roads.

Fiberglass plates, used in cold climate oilfields, provide temporary road surfaces. These interlocking plates are manufactured in 14 feet by 8 feet by 2 inch sections. The plates can carry very heavy loads over short distances without the need to construct structural roadbeds. This is good for areas like northwestern Alaska where the supply of construction aggregate is limited. The plates are expensive at about $2,000 per plate, but appear to have a very long lifespan.

Reduce exposed ground

Covered ground doesn't blow away and create dust. Each dirt parking area, footpath, shortcut, or eroding bluff can produce dust. Every new trail makes the problem worse.

Maintaining the native vegetation, tundra or woodland; replanting barren areas; planting gardens; and just driving only on designated roads or trails can all be dust control measures. Living plants not only cover the ground, but their roots hold soil together as well.

For more information, see: Healthy Tundra (PDF) and Revegetation (PDF)

Slow the wind

Windbreaks are barriers designed to slow the speed and redirect the flow of wind. These are not widely used in Alaska, but may be useful in some locations. Effective windbreaks do not stop the wind but break its forward movement, to slow it down. Good windbreaks will not create excessive turbulence or wind eddies. Windbreak materials may include picket and board fences (with gaps between pickets), berms, snow fences, and rows or hedges of plants. Windbreaks are most useful when designed for specific wind directions.

The effective zone of protection created by a windbreak is approximately 25 times its height, although maximum-protection wind reduction occurs in a range of 5 to 8 times the height of the screen. Therefore, if planning a windbreak 25 feet tall, the windbreak should be located 125 to 200 feet (5 to 8 times 25 feet) from the house for maximum usefulness. A 10-foot windbreak provides maximum protection to 75 feet and some reduction of wind (about 10 percent) up to 250 feet.

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