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OPTIMAL TIMING OF PAVEMENT PREVENTIVE MAINTENANCE TREATMENT APPLICATIONS SUMMARY As highway agency budgets shrink, more and more highway agencies are moving toward a policy of pavement preventive maintenance and away from worst-first pro- gramming (in which pavements are allowed to deteriorate to a highly distressed con- dition before any restorative work is performed). Preventive maintenance is a sys- tematic process of applying a series of preventive maintenance treatments over the life of the pavement to maintain a good condition, extend pavement life, and minimize life-cycle costs. Although pavement preventive maintenance is believed to result in lower agency costs, improved pavement conditions, and increased customer satisfac- tion, these programs continue to face many obstacles. Among these obstacles are lack of proof that preventive maintenance is cost effective and insufficient guidance on when preventive maintenance treatments should be applied. Consequently, highway agencies need a procedure that can help to demonstrate the cost-effectiveness of pre- ventive maintenance treatments and to provide guidance on the optimal timing of such treatments. PROJECT OBJECTIVES The primary objective of this research was to develop a methodology for determin- ing the optimal timing for the application of preventive maintenance treatments to flex- ible and rigid pavements. The methodology needed to be flexible enough to consider the variety of treatments that are used and the different ways of monitoring their per- formance. Also, the methodology needed to be useful both to agencies that already have a preventive maintenance program and to those considering the implementation of such a program. A secondary objective of the research was to create a user-friendly tool to aid in the implementation of this methodology. Applicability of the methodology was tested using data from actual pavement projects. A plan for obtaining the data needed to sup- port the proposed methodology was also developed to guide agencies not currently col- lecting preventive maintenance-related data.

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2 FINDINGS Researchers first contacted highway agencies in the United States and abroad to iden- tify the techniques that are being used to determine the optimal time to apply preventive maintenance treatments. It was found that there was almost no guidance available on this topic, and there was no indication of attempts to optimize the timing of treatment placement. Techniques used to determine the time to apply preventive maintenance included the following: A predetermined treatment schedule Time since a previous maintenance or rehabilitation event Maintenance surveys A pavement management system Because of the lack of available information from highway agency practice, the research focused on defining a methodology that could be used by agencies interested in placing the right treatment on the right pavement at the right time. The methodology is based on the premise that if a specific treatment is applied to a pavement at different times in its life, it will provide different benefits. Conceptually, there is a timing "win- dow" during the life of the pavement in which the maximum benefit from the mainte- nance treatment is attained, that is, the treatment will provide little to no benefit if it is placed either too soon or too late. This concept requires the use of a meaningful mea- sure of benefit. Benefit is defined in this research as the difference in condition over time between the treated pavement and the performance of the same pavement if no treatment had been applied. This definition allows benefit to be negative or positive. Because highway agencies use many different technologies and procedures to mon- itor and report on the performance of pavements, the methodology had to be flexible enough to include different measures of benefit. It was also necessary to address the fact that different measures of performance could be used by the same agency. For example, routinely collected monitoring information might include roughness, friction, and a measure of surface distress in the form of a composite index or single measures (e.g., rutting). Because the optimal time to apply a treatment is not solely when the greatest improvement in condition is realized but when the greatest improvement in condition is realized at the lowest cost, the methodology incorporates a comparison of benefit-cost ratios to identify the optimal timing. This comparison requires the ability to estimate the benefits and costs of applying a treatment at different times. While the optimal timing methodology is conceptually simple, its application is complex. A Microsoft Excel-based tool, OPTime, was developed to make the method- ology easy to apply. The resultant product is a versatile tool that allows users to ana- lyze existing pavement treatment performance data applied over a period of years to identify the optimal time to apply that treatment. Recognizing that agencies do not nec- essarily have data to analyze, the tool also has the capability to perform "what if" analy- ses with user-defined performance trends rather than with actual data. Because state highway agencies (SHAs) do not necessarily have all the data needed to perform an analysis, a plan for generating such data was developed. The plan offers guidance on selecting treatments to study, constructing test sections, and monitoring performance over time. Following the development of the optimal timing methodology and the analytical tool, the research team undertook a validation of the approach. Four SHAs (Arizona, Kansas, Michigan, and North Carolina) provided performance data for a range of treat- ments that were analyzed using OPTime. This analysis revealed the following findings:

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3 A wide range of performance measures are used to monitor pavement perfor- mance--not all of them clearly reflect the benefits of these treatments. Few SHAs are tracking all of the information that is needed to evaluate the effec- tiveness of treatments, such as pavement condition prior to treatment, the results of doing nothing, the pavement performance after treatment application, or defin- ing measures of pavement performance that reflect the benefit of applying pre- ventive maintenance. Agencies continue to use preventive maintenance treatments in "band-aid" appli- cations; these uses should be distinguished from preventive applications. Nonetheless, the validation effort demonstrated the soundness of both the analytical approach and the usefulness of OPTime. The report includes background information to introduce the concepts of preventive maintenance and facilitate the initiation or advancement of a SHA's preventive mainte- nance program. It also includes a methodology that can be used by SHAs to analyze exist- ing preventive maintenance-related data. The methodology is based on well accepted benefit and cost concepts and is presented on the OPTime Microsoft Excel-based tool. The analytical tool provides SHAs the flexibility of investigating many "what if" timing scenarios if relevant data are not available. The report also includes a plan for the design and data collection efforts required to obtain the data needed for the methodology. RECOMMENDATIONS Guidance and useful tools are available to assist with the implementation of a suc- cessful preventive maintenance program. The following actions should further enhance this implementation: Identify specific objectives of the preventive maintenance program to guide both the selection of preventive maintenance treatments and the measures used to mon- itor performance. Select treatments that are considered preventive applications and define guidelines on their appropriate use. Determine the expected performance of pavements when no treatment is applied (the "do-nothing" case) and the expected treatment performance using existing data or data from test sections constructed specifically for this purpose. Estimate the optimal timing of specific preventive maintenance treatments using an analytical tool such as OPTime.