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1Introduction The practice of pavement preservation (i.e., preventive maintenance [PM] and some forms of minor rehabilitation and corrective maintenance) is a growing trend among transportation agencies throughout the United States. However, the practice of preservation on high-traffic-volume roadways is not nearly as common as it is on lower-traffic-volume roadways. The following are possible explanations for this: ⢠Agencies may associate the use of specific PM treatments solely with low-volume roads, thereby assuming that they are not appropriate for other uses. ⢠Agencies may have concerns over the liability and risk associated with failure (when a treatment fails on a higher-volume roadway, more people are affected and more people complain). ⢠The benefits of preservation on higher-traffic-volume roadways might not be as readily recognized or as well documented. ⢠Preservation treatments may not be as effective on higher-traffic-volume roadways. They may deteriorate in different ways from those applied on low-volume roadways because of the higher standards used in design and construction of higher-traffic-volume roadways. Nonetheless, the preservation of high-traffic-volume roadways is as important as the preser- vation of lower-traffic-volume roadways, as many conditions hold true for both: ⢠Agency resources are limited and pavement preservation saves money in the long run. ⢠Preservation provides benefits to the traveling public, including safer and smoother roads. ⢠Preservation can be done more rapidly than rehabilitation, with fewer adverse effects on the traveling public. Admittedly, there are also challenges to the use of preservation strategies on high-traffic-volume roadways (e.g., a smaller toolbox of treatments that can be used successfully, more difficult treatment construction because of shorter available closure times, less available information on treatment performance and life, increased risk, and less available guidance on preservation strategies). Nonetheless, it is believed that the benefits of practicing preservation on high-traffic-volume roadways outweigh the challenges and that it is worthwhile to take steps to increase or improve the practice of pavement preservation on these roadways. The main objective of the research performed under SHRP 2 Renewal Project R26 was to develop guidelines on pavement preservation strategies for high-traffic-volume roadways that can be implemented and used by public agencies. A secondary objective was to identify promising pavement preservation strategies for application on high-traffic-volume roadways that might not commonly be used and to make recommendations for further research opportunities. Executive Summary
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 treatmentsâas measured by the extension in pavement service life imparted by the treatmentâis 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 2
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; 3
⢠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. 4 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) Surface and subsurface drainage characteristics Safety characteristics Friction/texture (e.g., FN, MPD/MTD, IFI) Crashes Pavementâtire noise Preliminary Set of Feasible Preservation Treatments Historical Design, Construction, and M&R Data Pavement type and cross-sectional design Materials and as-built construction Maintenance and rehabilitation (M&R) treatments (i.e., materials, thicknesses) Assess Needs and Constraints of Project Final Set of Feasible Preservation Treatments Performance Needs Targeted/required performance Expected performance of treatments Existing pavement condition effects Traffic effects (functional class and/or traffic level) Climate/environment effects Construction quality risk effects (agency and contractor experience, materials quality) Construction Constraints Funding Time of year of construction Geometrics (curves, intersections, pavement markings/striping) Work zone duration restrictions (i.e., facility downtime) Traffic accommodation and safety Availability of qualified contractors and quality materials Environmental considerations (e.g., emissions and air quality, recycling/ sustainability) Selection of the Preferred Preservation Treatment ⢠Conduct cost-effectiveness analysis Benefit-cost analysis Life-cycle cost analysis (LCCA) ⢠Evaluate economic and noneconomic factors Pavement Preservation or Major Rehab? Major Rehab Pavement Preservation Develop Feasible Rehab Treatments Figure ES.1. Process of selecting the preferred preservation treatment for high-traffic-volume roadways.
Implementation of Guidelines Implementation and use of the preservation guidelines by highway agencies will certainly involve working through a variety of institutional and external issues. Several key implementation bar- riers, such as resistance to allowing the use of lower-volume preservation treatments on higher- volume roads and the ability to convince the traveling public of the benefits and importance of preserving high-traffic-volume roads, were also formulated and presented in this report. Conclusions Several major conclusions were developed in this study. The most notable conclusions are the following: ⢠Several preservation treatments are currently being extensively used or have been documented as successfully used on high-traffic-volume roadways. ⢠Successful selection of projects and preservation treatments for high-traffic-volume roadways requires that Treatment functions be properly matched to pavement conditions; Potential effects of traffic level and climatic conditions on expected treatment performance be properly assessed; Project construction constraints be carefully examined in relation to the limitations of the treatments; and Treatment cost-effectiveness and other factors be properly and methodically considered. Recommendations Key recommendations from this study include the following: ⢠Develop a more comprehensive treatmentâpavement condition matching matrix; ⢠Improve estimates of treatment performance and unit costs; and ⢠Investigate more thoroughly the impact of pavement condition, traffic level, and climatic con- dition on treatment performance. 5
