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2 To accomplish these objectives, several sequential tasks were performed. First, an extensive literature search and review was undertaken to identify practices and experiences relating to preservation of high-traffic-volume roads. Next, a comprehensive survey of preservation practices was developed and distributed to all state highway agencies (SHAs) and selected other agencies to obtain information on current preservation practices for hot-mix asphalt (HMA)- and portland cement concrete (PCC)-surfaced pavements on high-traffic-volume roadways in rural and urban settings. Information from the compiled literature and the questionnaire survey was summarized and analyzed to identify the current state of the practice. Criteria were developed and applied to focus on preservation approaches that are currently successfully implemented and on others that have the potential to be successful but have not been regularly deployed. Detailed guidelines on pavement preservation strategies for high-traffic-volume roadways were then developed using the state of the practice and a comprehensive treatment selection framework and process. Findings Literature Review Results of the literature review revealed several important items concerning pavement preserva- tion practices in general and the use of preservation treatments on high-traffic-volume roads in particular. First, there are a variety of conventional preservation treatments (and several less widely used or new treatments) available for treating HMA- and PCC-surfaced roads, and these treatments have unique features and capabilities that can (a) effectively prevent the development of distresses or slow the development of existing distresses or (b) successfully restore the integrity and functionality of a pavement or restore important surface characteristics (e.g., friction and smoothness). The treatments entail the use of a variety of materials that can be placed in different fashions and in different thicknesses and that require different times until opening to traffic. Second, according to a 2004 National Cooperative Highway Research Program (NCHRP) survey of SHAs (Peshkin and Hoerner 2005), pavement preservation is occurring as frequently, or even more frequently in the case of rural roads, on higher-volume roadways than on lower-volume roadways. The results from that survey suggested that the more important distinction is between rural and urban roadways for any traffic volume. Third, besides proper design and good quality of construction and materials, the performance of preservation treatments--as measured by the extension in pavement service life imparted by the treatment--is impacted by three key factors. These factors include the following: · Condition of the existing pavement; · Level of traffic under which the treatment must function; and · Climatic conditions to which the treatment is exposed. Fourth, climatic conditions can also have an effect on the constructability of some preservation treatments. For example, some treatments, especially those based on asphalt emulsions, are best applied under restricted temperature and humidity conditions. Climate can directly affect curing time, which in turn impacts treatment feasibility and opening to traffic. Finally, various international preservation practices were identified and reported. The proper context for these strategies must be fully understood, because the way in which each country chooses their preservation strategy depends on their standard road design, climate, traffic patterns, and the political and economic organization of the country. Survey Results Results of the preservation survey revealed several key findings as well. First and foremost, SHAs have different definitions regarding what constitutes a high-traffic-volume roadway. The criteria
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3 range from an average daily traffic (ADT) as low as 1,000 vehicles per day (vpd) to as high as 100,000 vpd, and several agencies have separate criteria for roads in rural settings and those in urban settings (or, sometimes National Highway System [NHS] versus non-NHS roadways). To provide a more consistent analysis of preservation treatment usage on roadways with different traffic levels, an analysis of the survey responses regarding the high-traffic-volume criterion was performed. Based on this analysis, high traffic volume was defined as an ADT of at least 5,000 and 10,000 vpd for rural and urban roadways, respectively. The most commonly used preservation treatments (greater than 50% of responding agencies) according to these definitions of high-traffic-volume roadways were as follows: · Rural HMA-surfaced roadways: Crack filling, crack sealing, thin HMA overlay, cold milling and thin HMA overlay, and drainage preservation. · Urban HMA-surfaced roadways: Crack filling, crack sealing, cold milling and thin HMA overlay, and drainage preservation. · Rural and urban PCC-surfaced roadways: Joint resealing, crack sealing, diamond grinding, partial-depth repair, full-depth repair, dowel bar retrofitting (i.e., load transfer restoration), and drainage preservation. Treatments considered most inappropriate for use on high-traffic-volume facilities by survey respondents included fog seal, scrub seal, slurry seal, chip seal, and ultra-thin whitetopping for HMA-surfaced pavements and thin HMA overlay, ultra-thin bonded wearing course, and thin PCC overlays for PCC-surfaced pavements. The survey results indicated that the top three deficiencies addressed by preservation treatments on HMA-surfaced pavements are light and moderate surface distress (i.e., various forms of cracking), raveling, and friction loss. For PCC pavements, the top three pavement performance issues addressed related to smoothness or ride quality and surface distress (i.e., spalling and various forms of cracking), with some concern about noise issues. Finally, the survey results showed that an overwhelming number of respondents reported using overnight or single-shift closures for treatment application. Ultra-thin whitetopping on HMA-surfaced pavements and thin PCC overlays on PCC pavements were the exceptions, as they generally require longer closure times to allow for proper curing. Guidelines Development The results of the literature review and preservation survey provided valuable insights regarding the following preservation treatment attributes. Performance · Effect of existing pavement condition (distress) and serviceability (smoothness) on treatment performance; · Effect of traffic volume on treatment performance; · Effect of climate and environment on treatment performance; and · Effect of treatment on pavement condition, serviceability, safety (friction, surface drainage [splash/spray, cross slope]), and noise. Constructability Issues · Costs (agency and user); · Complexity of construction; · Availability of skilled and experienced or qualified contractors; · Need for specialized equipment or materials;
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4 · Availability of quality materials; · Climatic and environmental constraints; · Traffic disruption; · Traffic control constraints; and · Restrictions on available time for lane closures to complete the work. The information gleaned from the literature review and the survey results was combined with additional information, concepts, and ideas to develop a comprehensive preservation treatment selection framework and process. This process, shown in Figure ES.1, serves as the basis for the guidelines developed in the study. Current and Historical Pavement Performance Data (from field surveys and testing and/or PMS database) Overall condition indicator (e.g., PCI, PCR) Individual distress types, severities, and extents Smoothness (e.g., IRI, PI, PSI/PSR) Historical Design, Construction, and M&R Data Surface and subsurface drainage characteristics Safety characteristics Pavement type and cross-sectional design Friction/texture (e.g., FN, MPD/MTD, IFI) Materials and as-built construction Crashes Maintenance and rehabilitation (M&R) treatments Pavementtire noise (i.e., materials, thicknesses) Pavement Preservation Major Develop Feasible or Major Rehab Rehab Treatments Rehab? Pavement Preservation Preliminary Set of Feasible Preservation Treatments Assess Needs and Constraints of Project Performance Needs Construction Constraints Targeted/required performance Funding Expected performance of treatments Time of year of construction Existing pavement condition effects Geometrics (curves, intersections, Traffic effects (functional class and/or pavement markings/striping) traffic level) Work zone duration restrictions (i.e., Climate/environment effects facility downtime) Construction quality risk effects (agency Traffic accommodation and safety and contractor experience, materials Availability of qualified contractors and quality) quality materials Environmental considerations (e.g., emissions and air quality, recycling/ sustainability) Final Set of Feasible Preservation Treatments Selection of the Preferred Preservation Treatment · Conduct cost-effectiveness analysis Benefit-cost analysis Life-cycle cost analysis (LCCA) · Evaluate economic and noneconomic factors Figure ES.1. Process of selecting the preferred preservation treatment for high-traffic-volume roadways.