Preservation Approaches for High-Traffic-Volume Roadways (2011)

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82 The research described in this report was part of the SHRP 2 Renewal focus area, which addresses the need to complete long-lasting highway projects in a quick fashion with minimal disruption to the traveling public. The research focused on developing guidelines for the selection of preservation treat- ments for HMA- and PCC-surfaced pavements located on high-traffic-volume roadways. Key work activities included the following: • An extensive search and review of literature relevant to preservation practices in the United States and abroad; • A detailed questionnaire survey of highway agency preser- vation practices; • Detailed analysis of the project literature information and questionnaire survey results; • Identification of the current state of the practice for pre- serving high-traffic-volume roadways; • Development of criteria for identifying successful or poten- tially successful preservation techniques; and • Development of detailed guidelines for preservation strate- gies for high-traffic-volume roadways, including procedures for identifying feasible treatment options at the project level, evaluating their cost-effectiveness, and selecting the pre- ferred treatment based on various economic and non- economic factors. Conclusions The following are the major conclusions of the study: • High-traffic-volume definition. Based on the results of the preservation survey, it was found that highway agencies use different ADT criteria for classifying roadways as high volume. Moreover, in some agencies, the same classifica- tion criteria are applied to roads in rural and urban settings, whereas in other agencies, different criteria are used for roads in the two settings. To more accurately determine the types of treatments used on rural and urban high-traffic- volume roads, an analysis of the ADT classification criteria was performed, which resulted in the following definitions of high traffic volume: ADT ≥ 5,000 vpd for rural roadways and ADT ≥ 10,000 vpd for urban roadways. Although it is recognized that there will be agencies that find these limits to be too high or too low, the limits represent median values and can serve as a benchmark for future evaluations of preservation performance. • Preservation treatment options. A variety of treatments exist for preserving HMA- and PCC-surfaced pavements. Many of these treatments are already being used successfully on high-traffic-volume routes. Some treatments, such as fog seals and sand seals, are considered inappropriate for use on high-traffic-volume facilities. Others, such as slurry seals and chip seals, are deemed appropriate by some and in- appropriate by others. Still other treatments, such as crack sealing and joint resealing, are widely considered to be appropriate for use on high-traffic-volume roads. Highway agency practices, as determined through the preservation survey, indicate considerable use (≥20% of respondents) of 12 basic treatment types for high-volume, HMA-surfaced pavements and seven basic treatment types for high-volume, PCC-surfaced pavements. Some of these treatments can be further subdivided on the basis of variations in material components and construction processes. In any case, there is a variety of available treatments that are successfully being used in the preservation of high-traffic-volume roadways, and the list is constantly being expanded by the development and application of new products. • Preservation treatment functions. Pavement preservation treatments may be applied for two general purposes or func- tions: (1) prevention (or delay) of pavement distress devel- opment or slowing the development of existing distress and (2) restoration of functionality and serviceability of the pavement or improvement of its surface characteristics. To be effective, treatments must be matched with pavement C H A P T E R 5 Conclusions and Recommendations

83 distress types through an evaluation of treatment functions and distress causes and factors. This is especially important for higher-traffic-volume roadways, which many agencies have historically managed with structural enhancements rather than preservation. • Preservation treatment selection process. At the project level, the selection of treatments for high-traffic-volume roadways requires consideration and evaluation of many factors. A logical process for considering these factors begins with an assessment of the condition of the existing pavement and then progresses to an assessment of project needs and constraints. Following an evaluation of cost- effectiveness, it concludes with an assessment of both eco- nomic and noneconomic factors. On high-traffic-volume roadways, constraints, such as limited access times, and noneconomic costs, such as user delays, play a more sig- nificant role in the treatment selection process. • Consideration of pavement condition in treatment selection. To identify an initial list of feasible preservation treatments, begin by evaluating the current and historical condition of the existing pavement. The goal is to determine the types, severities, and extents of distresses and their rates of develop- ment as well as their probable causes. In this manner, treat- ments can be matched with pavement distress types through an evaluation of treatment functions and distress causes and factors. With their higher traffic volumes and loadings, deterioration rates and failure modes are not the same as for lower-traffic-volume roadways, and it should also be expected that treatment windows may be different. Decision support matrixes are a useful tool for identifying feasible treatments based on detailed pavement condition. Two deci- sion support matrixes—one for HMA-surfaced pavements and one for PCC-surfaced pavements—were developed in this study and are featured in Guidelines for the Preservation of High-Traffic-Volume Roadways. As a supplemental evalu- ation tool, the current and historical overall condition, ser- viceability, or roughness of a pavement can be tracked and compared with condition-based windows of opportunity previously established for each preservation treatment. • Consideration of project performance needs. When selecting a preservation treatment at the project level, the performance capabilities of the candidate treatments must be examined with respect to an established performance target or require- ment. Treatment performance is best measured in terms of the extension in service life imparted to the existing pave- ment by the preservation treatment. Investigation into the expected performance of several preservation treatments resulted in the identification of various performance ranges corresponding to a general application covering all traffic levels. Adjustments to these ranges were made to reflect the adverse impact of high traffic volumes on treatment durability and performance. The effects of existing pave- ment condition and climatic condition must also be taken into account when estimating treatment performance, as various studies have shown that small to moderate reduc- tions in performance can be expected when  Existing pavement condition is rated in the “fair” cate- gory rather than the “satisfactory/good” category; and  Climate is more characteristic of a freezing climate than a nonfreezing one, with significant snow and ice removal operations necessary for winter precipitation events. It is also recognized that the acceptance of relatively fre- quent applications of short-lived preservation treatments can be problematic on higher-traffic-volume roadways. • Consideration of project construction constraints. Candidate preservation treatments must also be evaluated for their ability to satisfy any specific construction constraints. Poten- tial constraints include available project funds, the antici- pated or targeted time frame (time of year) for construction, work zone duration restrictions, roadway geometrics, the availability of experienced contractors and quality materials, and traffic accommodation and safety issues. Of these, from an agency’s viewpoint, work zone duration and traffic accommodation and safety issues are more critical factors on the higher-traffic-volume roadways. However, the con- tractor can also contribute to a successful project by making sure that he is using a skilled crew and that QC practices are followed. • Evaluation of treatment cost-effectiveness. Cost-effectiveness analysis is an economic evaluation technique for comparing that which is sacrificed (cost) to that which is gained (per- formance benefit) for the purpose of evaluating alternatives. Two approaches for evaluating the cost-effectiveness of preservation treatments are identified in this study: equiva- lent annual cost (EAC) and benefit-cost ratio (BCR). EAC is a simpler approach that involves dividing the treatment unit cost by the expected treatment performance. BCR is a more detailed approach that involves calculating the long- term benefit of a treatment (using area under the pavement performance curve) and the life-cycle cost of the treatment, and dividing the former by the latter. Good unit cost and performance information for the alternative treatments are critical to each analysis technique. Moreover, because the analysis is focused on preservation of high-traffic-volume facilities, greater consideration should be given to evaluat- ing user costs. • Evaluation of economic and noneconomic factors. Although treatment cost-effectiveness is a major consideration in the selection of the preferred treatment, the reality is that several other factors are important to the decision-making process. A treatment decision matrix is an excellent way of rationally and systematically evaluating the different economic and noneconomic factors. It allows an analyst to weight the importance of the different factors, score the alternative treatments on each factor, and then generate overall scores using the individual factor weights and scores.

84 • Implementation of preservation guidelines. The preservation guidelines developed in this study are a useful tool for high- way agencies to identify candidate high-volume roadways suitable for pavement preservation and to select appropri- ate pavement preservation treatments. A wealth of informa- tion is included in the guidelines regarding the applicability and limitations of the various pavement preservation treat- ments and the process by which preservation treatments should be evaluated for selection at the project level. Agen- cies interested in implementing the guidelines can expect to encounter a variety of issues that may hinder the imple- mentation process. The most significant barriers entail institutional resistance to the use of certain treatments on high-volume roads, the ability to convince elected govern- ment officials and the traveling public of the importance of preserving good roads while some bad roads go untouched, and the external tug-of-war between competing pavement industry groups. Furthermore, because of their nature, a single failure on a higher-traffic-volume roadway can offset one hundred successes. At the roadway level, implementa- tion is advanced by monitoring and documenting the ben- efits of preservation. At the organizational level, experienced individuals within the agency championing the preservation program also play an important role in implementation. One of the objectives of this project was to identify prom- ising strategies or strategies that are not widely used that have the potential to be effective preservation treatments. These did not readily emerge from the literature review, outreach to industry and overseas contacts, or the surveys of agency prac- tice. However, the collected information clearly identifies some treatments that are used on high-traffic-volume road- ways by some agencies that others would not consider using. Agencies interested in extending their practice in many cases need look no further than the accepted practice of others. Recommendations Although an enormous amount of information on pavement preservation and preservation-related topics was gathered and analyzed in this study, there are still technical gaps in the treatment selection process that need to be addressed. Pro- vided below is a list of the most pressing issues and recom- mendations for addressing them in the future. • Develop a more comprehensive treatment-condition match- ing matrix. Such a matrix might use applicability ratings (1-to-5 scale, with 1 being nonapplicable, 3 being gener- ally applicable, and 5 being very applicable) that define how well a treatment addresses specific distress measures (i.e., a given distress type, severity level, and extent) and other condition parameters (i.e., overall condition, smooth- ness, friction, noise, and splash-spray). It would also use a weighting process to aggregate the individual applicability ratings for each treatment into an overall score. The overall scores of the treatments could be examined to identify fea- sible treatments—those with scores greater than or equal to a weighted 3. • Develop improved estimates of treatment performance on high-traffic-volume roadways. The expected performance ranges developed in this study are derived from estimates provided in the literature. Some estimates represent treat- ment life, while others represent extensions in pavement service life. As mentioned throughout this report, the appro- priate representation of treatment performance is the exten- sion in pavement service life. While it will be incumbent upon an implementing agency to establish its own estimates of treatment performance, the performance ranges pre- sented in this report need to be improved by incorporating pavement life extension data as it becomes available. • Investigate more fully the impact of pavement condition, traf- fic level, and climatic condition on treatment performance. Although implementing agencies will be tasked with evalu- ating and developing quantified estimates of treatment per- formance for different pavement conditions, traffic levels, and climate conditions, further research is needed at the national level, along the lines of the LTPP SPS-3 and SPS-4 studies. Such research should include more treatment types (including little-used but promising treatments and new or innovative treatments), cover the various climatic zones, and stratify according to specific pavement type (e.g., com- posite vs. flexible, jointed vs. continuous), different ranges of high traffic volume (e.g., 5,000 to 25,000 vpd, 25,000 to 50,000 vpd, ≥ 50,000 vpd), highway setting (urban vs. rural), and overall pavement condition (e.g., 65 ≤ PCR < 75, 75 ≤ PCR < 85, PCR ≥ 85) or serviceability/roughness. • Develop improved estimates of treatment unit costs. The treatment unit cost ranges provided are based on cost infor- mation contained in the literature. The cost ranges have been adjusted upward slightly, because the source data are a few years old. Although costs vary significantly from agency to agency and from project to project, a detailed evaluation of current costs would provide a better sense of the relative costs among treatments and would better capture the effects of increased oil prices in recent years. It is noted that the conclusions and recommendations pre- sented herein in many ways mirror the pavement preservation research needs priorities identified in the FHWA’s system preservation road map (FHWA 2008). While the problem statements in that document are not specifically aimed at preservation for high-traffic-volume roadways, the mix of top- ics identified as the highest priority are similar to needs identi- fied in this research. It is reasonable to conclude that as the research needs identified in the road map are addressed, and if attention is paid in particular to high-traffic-volume roadways as considered in this research, then the practice of preservation on high-traffic-volume roadways will continue to advance.