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NCHRP Synthesis 485: Converting Paved Roads to Unpaved

NCHRP Converting Paved Roads to Unpaved cover page

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Highway administrators, engineers, and researchers often face problems for which information already exists, either in documented form or as undocumented experience and practice. This information may be fragmented, scattered, and unevaluated. As a consequence, full knowledge of what has been learned about a problem may not be brought to bear on its solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recommended practices for solving or  alleviating the problem.

There is information on nearly every subject of concern to highway administrators and engineers. Much of it derives from research or from the work of practitioners faced with problems in their day-to-day work. To provide a systematic means for assembling and

evaluating such useful information and to make it available to the entire highway community, the American Association of State Highway and Transportation Officials-through the mechanism of the National Cooperative Highway Research Program-authorized  the Transportation Research Board to undertake a continuing study. This study, NCHRP Project 20-5, "Synthesis of Information Related to Highway Problems," searches out and synthesizes useful knowledge from all available sources and prepares concise, documented reports on specific topics. Reports from this endeavor constitute an NCHRP report series, Synthesis of Highway Practice.

This synthesis series reports on current knowledge and practice, in a compact format, without the detailed directions usually found in handbooks or design manuals. Each report in the series provides a compendium of the best knowledge available on those measures found to be the most successful in resolving specific problems.

Preface:

By Jon M. Williams, Program Director

Transportation Research Board

This study found that the practice of converting paved roads to unpaved is relatively wide-spread; recent road conversion projects were identified in 27 states.  These are primarily rural, low-volume roads that were paved when asphalt and construction prices were low.  Those asphalt roads have now aged well beyond their design service life, are rapidly deterioration, and are both difficult and expensive to maintain.  Instead, many local road agencies are converting these deteriorating paved roads to unpaved as a more sustainable solution.

Key findings from this study include: Local road agencies have experienced positive outcomes by converting roads. Many local road agancies reported cost savings after converting, compared with the costs of continuing maintenance of the deteriorating paved road, or repaving.  One key to successful conversion is early involvement of the public in the planning process. Other techniques that can be used to improve the overall results of a project include treating or stabilizing granular surfaces to control dust, limiting the rate of aggregate loss, and reducing motor grader/blade maintenance frequency.  Stabilization procedures can also improve safety, increase public acceptance, and reduce life-cycle costs and environmental impacts after a conversion has taken place.

Laura Fay and Ashley Kroon, Western Transportation Institute, Montana State University; Ken Skorseth and Richard Reid, South Dakota State University; and David Jones, University of California, Davis, collected and synthesized the information and wrote the report.  The members of the topic panel are acknowledged on the preceding page.  This synthesis is an immediately useful document that records the practices that were acceptable within the limitations of the knowledge available at the time of its preparation.  As progress in research and practice continues, new knowledge will be added to that now at hand.

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