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5 low-volume roads are defined as roads with AADT of less than 250 vehicles, based on research that determined that converting paved roads to unpaved was cost-effective at this threshold (Mustonen et al. 2003; Sacramento Area Coun- cil of Governments 2008; Iowa Local Technical Assistance Program 2012). Other studies found that gravel road sur- faces can be effective when AADT is less than 170 vehicles (Skorseth and Selim 2000). On roads with AADT greater than 170 vehicles, significant aggregate loss, higher dust levels, and more frequent blading requirements were experienced. The current study found that many roads that have been con- verted from paved to unpaved in recent years had an AADT of 21 to 100 vehicles, suggesting that most of the roads currently being converted should not have been paved initially because of inadequate structural support (underdesign) or that road usage patterns have changed significantly since paving. STUDY OBJECTIVES Many counties and some states have already begun the process of identifying low-volume roads that can be converted from paved to unpaved. However, there is a lack of information available to public agencies on managing these conversions. The objectives of this synthesis are to identify the state of the practice of road conversions from paved to unpaved by: â¢ Defining the terms âvery low-volume roadâ and âunpavedâ in the context of road conversion projects, â¢ Identifying agencies that have converted roads from paved to unpaved, â¢ Identifying metrics used by road agencies in the con- version process, â¢ Identifying tools, such as databases or software, and pro- cedures that have been used in deciding when and how to convert a road from paved to unpaved, â¢ Identifying and synthesizing information on decision- making parameters and impacts of road conversions, â¢ Documenting public outreach efforts, and â¢ Identifying knowledge gaps and research needs on this topic. STUDY APPROACH An extensive literature review of national and international sources was conducted to gather information on converting paved roads to unpaved roads. Technical documents, govern- ment reports, journal publications, conference presentations BACKGROUND Current transportation asset management practices assume that roads will be preserved to maintain the current level of service or structural condition, or improved to enhance the structural and surface condition and ride quality. In addition, the historic trend has been to reduce the number of unpaved system lane-miles. These policies were developed in the last century when the costs of asphalt, fuel, and all construction expenditures were low compared with current costs and the axle loads carried on rural low-volume roads were significantly lighter than current loads. The rising cost of asphalt and fuel and a significant increase in traffic and traffic loads on low- volume rural roads associated with commercial, agricultural, and energy sector development, combined with stagnant or decreasing budgets, are causing a situation in which the cost of rehabilitating and maintaining very low-volume paved roads on the existing road network often is no longer feasible (Figure 1). Historically, unpaved roads have been considered the lowest level of service provided. In a demonstration of progress and an effort to improve road conditions for rural residents, many agencies paved low-volume roads with little or no base prepa- ration when asphalt and construction prices were low. Those asphalt roads have now aged well beyond their design service life, are deteriorating rapidly, and are difficult and expensive to maintain. The increasing size of agricultural and commer- cial equipment, including that used by the energy sector, com- pounds this deterioration in many areas. Traditionally, these roads were maintained or repaved at regular intervals, but with the increasing traffic loads, the increasing cost of materials, and stagnant or declining road maintenance budgets, many agen- cies do not have the funding to support these activities. Instead, many local road agencies are looking to convert deteriorated paved roads to unpaved surfaces as a more sustainable solution (Figure 2). The process of converting a low-volume road from paved to unpaved is another tool in the toolbox that is a viable alternative to maintaining the road as a paved surface or reha- bilitating it to an appropriate level of paved surface. DEFINING LOW-VOLUME ROADS FOR THE PURPOSE OF THIS STUDY The Guidelines for Geometric Design of Very Low-Volume Local Roads defines a low-volume road as having annual aver- age daily traffic (AADT) of 400 vehicles or less (AASHTO 2001). For the purpose of this project, low-volume or very chapter one INTRODUCTION
6 and proceedings, and newspapers and online media publica- tions were reviewed. Local, state, federal, and international government and organization web pages, manuals, field guides and reports, and published specifications also were studied to develop the content of this report. Information captured in the literature review was used to develop a survey questionnaire. The survey questionnaire was used to gather additional information on converting paved roads to unpaved roads. The purpose of the survey was to identify locations where road conversions have occurred or will occur and locations being considered for conversion. It was also used to cap- ture basic information on road conversions that have been performed. A total of 140 responses were received from the survey; they are discussed in relevant sections of the current report. The survey questionnaire appears in Appendix A, and a summary of the survey results is provided in Appendix B. Follow-up interviews were conducted with 17 survey respondents who were selected based on their survey responses. Information gained from interviews has been incorporated into relevant sections of the report and used to create a summary of case examples. A list of interviewees and their contact infor- mation can be found in Appendix C, and the developed case examples appear in Appendix D. Additional case examples and information on road conversions can be found in Appendix E. This report consists of five chapters: â¢ Chapter one: Introduction and background on converting roads from paved to unpaved, an outline of the need for this synthesis report, and the objectives for the study. â¢ Chapter two: Summary of the state of the practice of con- verting roads, including how âvery low-volume roadsâ are defined, a literature review, and results of the survey and subsequent interviews. These are summarized by the processes typically followed in deciding whether a road should be converted and how the conversion is done. Information is provided on road maintenance and pavement condition assessment tools, public outreach efforts, and public reaction to road conversion projects. The impacts of road conversion projects in terms of changes in traffic patterns, equipment, and staffing; envi- ronmental impacts; safety; and the costs of converting and maintaining converted roads are also included. â¢ Chapter three: Summary of the survey results and responses from follow-up interviews. â¢ Chapter four: Relevant reports, documents, and resources that can be used when considering or conducting a road conversion project. â¢ Chapter five: Summary of the findings on the state of the practice of converting paved roads to unpaved roads and suggestions for future work on this topic. Additional information is provided in a glossary and appendices: the survey questionnaire (Appendix A), a sum- mary of the survey results (Appendix B), list of interviewees with contact information (Appendix C), case examples and supplemental information (Appendix D and Appendix E), a sample letter used to notify the public of a proposed road conversion project (Appendix F), and a research needs state- ment developed based on knowledge gaps identified through this research project (Appendix G). FIGURE 2 A local road that has been converted to a gravel surface. The township is able to maintain the road in acceptable condition with available funds. (Photo courtesy of K. Skorseth.) FIGURE 1 A failing asphalt road (a), and a close-up showing breakup of the pavement surface (b). (Photos courtesy of D. Jones.) (a) (b)