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OCR for page 79
C H A P T E R 5 Conclusions and Recommendations The research described in this report was part of the SHRP 2 types of treatments used on rural and urban high-traffic- Renewal focus area, which addresses the need to complete volume roads, an analysis of the ADT classification criteria long-lasting highway projects in a quick fashion with minimal was performed, which resulted in the following definitions disruption to the traveling public. The research focused on of high traffic volume: ADT 5,000 vpd for rural roadways developing guidelines for the selection of preservation treat- and ADT 10,000 vpd for urban roadways. Although it ments for HMA- and PCC-surfaced pavements located on is recognized that there will be agencies that find these limits high-traffic-volume roadways. Key work activities included to be too high or too low, the limits represent median values the following: and can serve as a benchmark for future evaluations of preservation performance. An extensive search and review of literature relevant to Preservation treatment options. A variety of treatments exist preservation practices in the United States and abroad; for preserving HMA- and PCC-surfaced pavements. Many A detailed questionnaire survey of highway agency preser- of these treatments are already being used successfully on vation practices; high-traffic-volume routes. Some treatments, such as fog Detailed analysis of the project literature information and seals and sand seals, are considered inappropriate for use questionnaire survey results; on high-traffic-volume facilities. Others, such as slurry seals Identification of the current state of the practice for pre- and chip seals, are deemed appropriate by some and in- serving high-traffic-volume roadways; appropriate by others. Still other treatments, such as crack Development of criteria for identifying successful or poten- sealing and joint resealing, are widely considered to be tially successful preservation techniques; and appropriate for use on high-traffic-volume roads. Highway Development of detailed guidelines for preservation strate- agency practices, as determined through the preservation gies for high-traffic-volume roadways, including procedures survey, indicate considerable use (20% of respondents) of for identifying feasible treatment options at the project level, 12 basic treatment types for high-volume, HMA-surfaced evaluating their cost-effectiveness, and selecting the pre- pavements and seven basic treatment types for high-volume, ferred treatment based on various economic and non- PCC-surfaced pavements. Some of these treatments can be economic factors. further subdivided on the basis of variations in material components and construction processes. In any case, there Conclusions is a variety of available treatments that are successfully being used in the preservation of high-traffic-volume roadways, The following are the major conclusions of the study: and the list is constantly being expanded by the development and application of new products. High-traffic-volume definition. Based on the results of the Preservation treatment functions. Pavement preservation preservation survey, it was found that highway agencies treatments may be applied for two general purposes or func- use different ADT criteria for classifying roadways as high tions: (1) prevention (or delay) of pavement distress devel- volume. Moreover, in some agencies, the same classifica- opment or slowing the development of existing distress and tion criteria are applied to roads in rural and urban settings, (2) restoration of functionality and serviceability of the whereas in other agencies, different criteria are used for pavement or improvement of its surface characteristics. To roads in the two settings. To more accurately determine the be effective, treatments must be matched with pavement 82

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