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18 CHAPTER 3 RESEARCH RESULTS INTRODUCTION mately, a methodology very similar to the cost-effectiveness analyses used in pavement management systems was selected. There is a need to identify when it is "best" to apply pre- ventive maintenance treatments. Treatment performance is greatly dependent on the condition of the pavement at the Overview of the Analysis Approach time of treatment application, and different types of treat- ments are likely only to be effective when placed at certain The approach is built on a number of fundamental con- cepts. It assesses the effectiveness of a particular preventive times in a pavement's life. When placed at the right time, a maintenance application in terms of both the benefit it pro- preventive maintenance treatment becomes a cost-effective vides and the cost required to obtain that benefit. In this means of attaining the desired life and performance of the methodology, benefit is defined as the quantitative influence pavement. Treatments applied too soon add little benefit and on pavement performance as measured by one or more con- treatments applied too late are ineffective; however, there is dition indicators. Costs that may be included in the analysis little guidance available on this topic. include the following: There are no studies that have successfully determined how to identify the optimal time to apply preventive mainte- The agency cost to construct the treatment, nance treatments; although a number of completed studies Work zone-related user delay costs, have examined this issue and other research continues to The cost of a rehabilitation activity that would be con- study it. These include the studies of maintenance effective- sidered at the point when the preventive maintenance ness under the Specific Pavement Studies (SPS-3 and SPS-4) treatment is considered failed, and effort (17, 18), and field studies by the DOTs in Iowa (9), Ari- The cost of scheduled routine maintenance. zona (19), Texas (20, 21), and South Dakota (22). The primary objective of this project was to determine an In the optimal timing methodology, the benefits associated approach for identifying the optimal timing for the application with the use of a preventive maintenance treatment are eval- of preventive maintenance treatments. This chapter describes uated in conjunction with its associated costs. The optimal a methodology for determining the optimal time to apply pre- application of a preventive maintenance treatment occurs at ventive maintenance by analyzing pavement performance the point at which the benefit per unit cost is greatest. and cost data. The methodology is presented as a Microsoft Excel-based software designated OPTime. The results of an evaluation of OPTime (and the analysis methodology) with Pavement Performance data provided by state highway agencies is also described. The computation of the benefit associated with an applied preventive maintenance treatment requires knowledge of the anticipated performance of the pavement. The effect of a treat- INTRODUCTION TO THE METHODOLOGY ment on performance is determined by the change in condition USED TO DETERMINE OPTIMAL TIMING indicators, such as International Roughness Index (IRI), pres- ent serviceability index (PSI), or other custom-defined mea- One of the initial challenges in this project was to attach sure of performance. some physical meaning to "optimal" timing in the context of preventive maintenance treatment applications. It could potentially mean to provide the smoothest ride for the least Condition Indicators money, to prolong the need for rehabilitation, or to meet some other objective. While the concept of "optimal" tim- The ability of treatment to preserve pavement condition and ing seems closely linked to cost-effectiveness, the defini- retard future deterioration is measured by changes in the con- tion of cost-effectiveness also varies among agencies. Ulti- dition indicators that define pavement performance. Condition