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A Successful Practitioner's Handbook

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Designing and implementing an unpaved road improvement program requires a comprehensive understanding of specific site, road, and traffic characteristics and, depending on how a practitioner goes about it, can lead to different decisions about what is the most appropriate dust control solution for an unpaved road.


Finding and accessing readily available, user-friendly published information on establishing an unpaved road improvement program incorporating dust control appears to be an unmet need and concern for many unpaved road managers. Consequently, managers often rely on additive suppliers and vendors for guidance who, understandably, will encourage the use of their product even though it may not be the best solution for a particular section of road. Competing suppliers and vendors may also provide conflicting advice, leaving the road manager in doubt as to which approach to take.

Cover of report


Road manager experience in establishing unpaved road improvement programs varied considerably across the locations visited. In some locations, road managers had researched the topic, typically following the US Forest Service Dust Palliative Selection and Application Guide and experience and/or recommendations from other experienced managers in neighboring jurisdictions. In other locations road managers relied on information and recommendations from suppliers and vendors. Most scan tour hosts were unaware of how additives were categorized, the full extent of available additives, or how to select an appropriate additive with confidence for a particular situation.

Data Gathering

The first task in establishing an unpaved road improvement program, with specific emphasis on using chemical treatments, is to document the features of the unpaved roads in the network. This includes a survey of the road and adjacent land, and possibly working with the road users and those who live next to it to understand public perceptions of problems with the road.

Information that needs to be collected includes:

  • Road alignment and geometry (Figure 18), including drainage and the presence of shoulders, and highlighting any areas that typically require additional maintenance and/ or repairs, or that are considered accident "black spots." The steepness of the grade may limit the choice of chemical treatment.
  • Adjacent land use, such as residential, crops, forest, and wetland (Figure 19).
  • Road condition, (poor, average or good) with a reason for the rating (no or poor aggregate, inadequate drainage, dust, surface distresses of washboarding, potholes, ruts, erosion, and weak subgrade). Problems should be divided into those that can be corrected using routine maintenance and those that will require reconstruction and/or regravelling.
  • The thicknesses of the wearing and base courses (Figure 20) and their material properties (that is, using simple laboratory tests that determine the particle size distribution [grading] and plasticity [Atterberg Limits]. If passability problems are experienced in wet conditions, strength tests [California Bearing Ratio] should also be conducted). Interpretation of the results is covered in Chapter 5. Wearing course thickness should typically be greater than 4 in. (100 mm), while base course thickness must be sufficient to raise the road above surrounding ground level and to "protect" the subgrade from rutting.
  • The ability of the road to shed water (that is, is there sufficient crown?). A crown of between 4 and 5 percent is adequate for water to flow off the road (Figure 21). Less crown typically results in ponding of water along the centerline, leading to potholes and ultimately softening of the material resulting in passability problems. More crown often leads to erosion and dangerous driving conditions (truck trailers can slide off the crown). Side drains need to take the water away from the road to prevent ponding on the sides that can lead to softening of the subgrade and resulting poor passability.
  • The average daily traffic volume (Figure 22), primary users (for example, commuters or haul vehicles), types of vehicles (that is, percentage of trucks and cars), seasonality of traffic (that is, are there peak periods during harvesting?), and whether there is loaded truck traffic in one direction and unloaded in the other (fast moving empty trucks tend to cause more rapid deterioration on unpaved roads than slower moving loaded trucks).
  • Average speed of the vehicles and what governs this speed (for example, road condition, dust, enforcement, etc.). The road manager will need to predict whether speeds will increase after dust control and whether this will lead to unsafe driving conditions.
  • Known problem areas that require constant maintenance/repair or that constantly generate public complaints and the reason(s) for the problem (Figure 23).
  • The current regravelling and grader maintenance program and frequencies.
  • The current funding levels and whether additional funding can be made available if chemical treatments can be justified, and whether a multi-year program will be considered to optimize spending in the longer term.
  • An acceptable level of dustiness (Figure 24). Complete dust control is generally only achieved by upgrading a road to a paved standard, the costs of which are often prohibitive and unjustifiable for low traffic volumes. Road users and adjacent property owners will often gladly accept a percentage of dust reduction. Ask these individuals to rate what an acceptable level of dust control is.
  • The long-term plan for each road (that is, will it continue to experience current average daily traffic [ADT] and usage types or is ADT increasing? Will it be closed or paved in the next few years? Will improving it with a chemical treatment attract more traffic?).
  • Climatic conditions, including rainfall distribution and intensity of storms, annual humidity ranges, freeze/thaw conditions, and maximum temperatures.

Figure 18. Photo. Super-elevation on sharp curve.

Figure 19. Photo. Mixed adjacent land use.

Figure 20. Photo. Insufficient, poor quality gravel.

Figure 21. Photo. Road with good drainage.

Figure 22. Photo. Truck on treated road.

Figure 23. Photo. Potholes caused by poor drainage.

Figure 24. Photo. Acceptable dust level.


Based on the data collected, the road manager will need to rank the roads for improvement. The criteria used for this condition ranking will initially depend on the type and levels of distress, but may also be influenced by public complaints, political intervention, and/or funding mechanisms. Not all roads will require chemical treatment. When considering chemical treatment, it is often best to first treat those roads that have adequate gravel thickness and are in good condition (that is, keep the "good roads good" [Figure 25]) and then to improve and treat the poorer quality roads
(Figure 26). This strategy is usually more cost- effective in the long run and will ultimately bring all roads to an acceptable standard faster than by adopting a "worst first" strategy (fixing bad roads first costs a lot, leaving limited or no funds to maintain the good roads, which will quickly deteriorate to a poor condition).

Figure 25. Photo. Keeping a good road good.

Figure 26. Photo. Road requires upgrade before treatment.


Example case studies are provided in Figure 27.

Case Studies

1) A logging road in the Pacific Northwest has heavy seasonal traffic of lumber haul trucks (High average daily traffic [ADT]), considerable dust generation in the summer, is subject to freeze/thaw cycles in winter and spring snow melt as ell as seasonal rains in spring and fall, with the base and surface sources worn below minimums and with significant washboarding. Dust control is clearly needed to alleviate the safety issues related to reduced visibility for haul trucks and prevent dust falling into streams. Before any chemical dust control is applied, a cost-effective solution for this road would likely be to apply and grade a new base and surface courses to the specified thicknesses, followed by incorporation of a durable or regionally prove stabilizer/dust control additive into the surface course.

Figure 27. Case studies illustrating the need for appropriate strategies for local conditions.

2) A campground/trail head access road in the Southwest is dry most of the year, has seldom freeze/thaw cycling, with a low ADT of mostly light-duty vehicles, occasional heavy summer monsoon rains and occasional mild frontal winter rains. The road is seldom, if ever, re- graded. Only limited, thin surface course is present, which is in fairly good condition with dust needing to be controlled for aesthetic and environmental reasons. In this case, a topical application and minimal road preparation may be sufficient.

Figure 27. Case studies illustrating the need for appropriate strategies for local conditions (cont.).

3) A rural road in the Midwest has moderate ADT, mixed traffic types including light duty vehicles and seasonal farm equipment, some rutting and ponding of water on the road surface is known to occur, freeze/thaw cycling in winter, significant spring precipitation can be expected. Summer dust control is needed because of nuisance dust affecting residents in adjacent homes and businesses and because of road safety issues. The road is periodically graded to restore the crown and remove the potholes and minor rutting. In this situation, an incorporation method, applied in concert with the annual regrading and road reshaping, may be the best approach.

Figure 27. Case studies illustrating the need for appropriate strategies for local conditions (cont.).

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