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5 oration occurs in the form of rutting, cracking, loss of surface type, surface thickness, pavement deterioration (type, sever- texture, increased roughness, and other deterioration. In ity, and extent), past and projected traffic, performance his- concrete-surfaced (rigid) pavements, the initial deterioration tory, maintenance history, treatment costs and available bud- may take the form of cracking, loss of surface texture, gets, and expected future performance. In some cases, the increased roughness, and the intrusion of water and incom- analysis is performed as part of the agency's pavement man- pressibles into joints and cracks. The concept of preventive agement process. However, there was no apparent rigorous maintenance stipulates that these deterioration modes can be analytical process for timing or selecting preventive main- anticipated and at least partially mitigated before they occur, tenance treatments. A brief summary of the results of this thereby providing the following long-term benefits: data collection effort is found in Appendix A (not published herein). A higher level of service resulting from improved pave- ment performance, reduced user costs, and increased Task 2. Identify appropriate preventive maintenance safety; treatments for ranges of climatic conditions, traffic lev- Delayed need for rehabilitation; and els, and pre-treatment pavement conditions. Many factors Life-cycle cost savings were found to be important for identifying appropriate pre- ventive maintenance treatments although ultimately the deci- sion is based on "local" factors. General guidance is available OBJECTIVE AND SCOPE OF RESEARCH on the conditions in which various treatments are appropriate. As described in Chapter 2, this guidance can be adapted by The objective of this research was to develop a methodol- agencies to meet their needs. ogy for determining the optimal timing for the application of preventive maintenance treatments to flexible and rigid pave- Task 3. Recommend and describe a methodology that ments to realize the greatest increase in performance at the considers the cost-effectiveness and performance of main- least cost. The methodology was to consider the variety of tenance treatments. The optimal timing methodology is treatments that are used and the different ways of monitoring described in Chapter 3. The process that led to its adoption is pavement performance. It should be useful both to agencies described in Appendix B (not published herein). that already have a preventive maintenance program and to those considering the implementation of such a program. Task 4. Create a user-friendly analysis tool to facilitate This research addresses a gap in preventive maintenance use of the methodology for the variety of pavement main- programs that has been recognized by highway agencies. In tenance situations encountered by highway agencies. The response to a November 2000 survey of SHAs, 12 respon- optimal timing methodology, designated OPTime, is a Visual dents (out of 34) identified data collection and management Basic Application-driven Microsoft Excel workbook pro- and 6 identified improved models and guidance on project vided on a CD-ROM. OPTime can be used to estimate the selection as the most important needs for their preventive optimal time to apply a specific preventive maintenance maintenance program (7). The comments provided with the treatment. Although OPTime does not use a true optimiza- responses pointed out the lack of research that specifically tion strategy (i.e., all possible treatment application times and correlates maintenance treatments to the extension of pave- alternative treatments are not analyzed), it provides a simple ment life cycle, the lack of information on how often preven- analysis method that can be used to choose the most effec- tive maintenance treatments should be applied, the necessity tive treatment timing from a set of user-chosen timing sce- to articulate definite cost savings and benefits, and the reliance narios (i.e., a preventive maintenance treatment applied at on experience for determining appropriate preventive main- many different user-chosen pavement ages). A User's Guide, tenance treatment timing. found in Appendix C, http://trb.org/news/blurb_detail.asp?id =4306 offers specific instruction on the use of the tool. RESEARCH APPROACH Task 5. Demonstrate the applicability of the methodology The project objective was accomplished by completing the and the suitability of the implementation tool using data following six tasks. from a limited number of projects or other means. The Ari- zona, Kansas, Michigan, and North Carolina DOTs all pro- Task 1. Collect and review information on the timing, vided data and other resources to support the effort to evaluate selection, and performance of preventive maintenance the methodology using the analysis tool. Since the availability treatments of flexible and rigid pavements. Highway agen- and type of data greatly differed between agencies, the col- cies in North America, South Africa, and New Zealand were lected data were also used to test the flexibility of the analy- queried about their preventive maintenance experiences, par- sis tool. The results of this effort are discussed in Chapter 3. ticularly as they relate to treatment timing and project selec- tion. Agencies reported that they consider a range of factors Task 6. Develop a plan, for use by highway agencies, to col- in their decision process, including environment, material lect the data needed to support the proposed methodology.