Previous work (NCHRP Synthesis 485: Converting Paved Roads to Unpaved) that synthesized the state-of-the-practice of converting paved roads to unpaved roads identified a need for guidelines that highlight effective practices in the realm of:
Objective methods for the identification of roads that are suitable candidates for conversion;
Information on how to successfully convert a road;
Guidance for outreach, communication to the public, and visualization tools.
To date very limited information is available on roads that have been converted from paved to unpaved, and what information is available often comes in the form of newspaper articles and anecdotal accounts of road conversions. The purpose of the proposed guide is to document proven, effective practices that can be used in road conversion projects. The document will serve as a formal and peer reviewed information source that local road agencies can use when road conversions are being considered. The use of the guide and acceptance of the practice of converting from paved to unpaved surfaces (unpaving) will provide a case for the acceptance of road conversions as another pavement management technique.
While low volume roads are typically identified as having an annual average daily traffic (AADT) of less than 400, roads that are appropriate candidates for conversion will typically have an AADT of less than 150. These roads are often used to access homes, are used by agricultural and extraction industries, or serve to access recreational areas. The wide variety of road users, traffic patterns and vehicle types are factors that need to be considered in the decision to unpave a road. Other factors include road condition, safety, required maintenance, as well as a life-cycle cost comparisons of different options, such as; continued maintenance of the deteriorating road, rehabilitating the paved road, or converting the road to an unpaved surface. By identifying candidate roads for conversion, local road agencies can more effectively manage dwindling budgets.
Road conversions are currently being undertaken without supporting documents or knowledge and typically involve pulverizing the deteriorating surface and mixing it with the underlying base materials. Supplemental material may be added where required and in some instances the mixed material is stabilized with an appropriate chemical treatment. The processed materials are then compacted and shaped. Some converted roads are treated with dust abatement products. Once the road has been converted, follow up maintenance is required in the form of blading, reapplication of dust abatement products, and periodic regravelling.
The extent of knowledge on this topic is very limited, but the practice of converting roads to unpaved is becoming more and more common. This is occurring in a climate where budgets for local road agencies are decreasing and for some, pavement deterioration is accelerating due to heavy vehicles which often exceed legal load limits.