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24 Treatment Selection roadway friction with a friction number of 60 (i.e., FN40R = 60). If the application of a particular treatment Agencies use a broad range of treatments in pavement is found to result in friction numbers greater than 60, the preservation and rehabilitation programs. However, preven- area above the upper benefit cutoff value of 60 would tive maintenance, which is a subset of these two pavement not be included in the benefit calculations. activity categories, considers treatments that can be applied to Lower benefit cutoff value--The lower benefit cutoff a pavement in good condition to preserve condition and pre- value is the lower limit to the benefit area computations vent or delay future deterioration. The treatments shown pre- (i.e., no area below the lower benefit cutoff level is viously in Table 2 fit this definition of preventive maintenance counted as a benefit). For a condition indicator relation- and will provide benefits when used in the appropriate condi- ship that decreases over time this value also serves as tions. The user should, however, carefully consider whether the benefit cutoff value in determining the analysis period these benefits can be measured using available performance (in the same manner as described for the upper benefit evaluation procedures. For example, crack sealing or main- cutoff). taining drainage features may be a cost-effective means of maintaining or improving pavement condition, but perfor- mance measures such as IRI, cracking indices, rutting, and Figure 2 illustrates how upper and lower benefit cutoff values faulting may reveal only subtle (or even no) differences when limit the area calculations for both decreasing and increasing compared with control sections. do-nothing condition indicator curves. In this example, the Furthermore, while the analysis method permits users to decreasing relationship is limited by both the upper and lower analyze performance results from any specified treatment, benefit cutoff values and the increasing relationship is limited the approach does not work well for treatments applied when only by the upper benefit cutoff value. the pavement is deteriorated and rehabilitation is required. Benefit cutoff values are unique to an agency, and perhaps The current approach allows the analysis of a single applica- even to a given project, and their determination is not straight- tion of one preventive maintenance treatment but not that of forward. In general, agencies should consider benefit cutoff a series of preventive maintenance treatments. values that relate to the following identifiable condition levels: Selection of Application Ages DECREASING RELATIONSHIP The optimal time to apply a selected preventive mainte- nance treatment is estimated by conducting analysis for dif- Upper benefit cutoff value ferent timing scenarios in which the treatment is applied at different pavement ages. Condition Indicator Lower benefit cutoff value Step 2: Selection of Benefit Cutoff Values The concept of optimal timing stipulates that treatments Area limited by benefit applied too soon or too late do not necessarily provide added cutoff values benefit. Benefit cutoff values are defined as the y-axis (con- dition indicator) boundary conditions for the performance Age, years curves that define the upper and lower limits for the benefit area calculations. The specific definitions of the upper and INCREASING RELATIONSHIP lower benefit cutoff values are as follows: Upper benefit Area limited by benefit cutoff value Upper benefit cutoff value--The upper benefit cutoff cutoff values value is the upper limit to the benefit area computations Condition Indicator (i.e., no area above the upper benefit cutoff level is included in the benefit computation). For a condition indicator relationship that increases over time (e.g., IRI), Lower benefit cutoff value this value also serves as the benefit cutoff value that is used in determining the analysis period (i.e., the age at which the performance curve reaches the benefit cut- off value). For a condition indicator relationship that Age, years decreases over time (e.g., friction number), the upper benefit cutoff value defines a "ceiling" that limits the Figure 2. Illustration of the application of upper and benefit credited to the application of the treatment. For lower benefit cutoff values on both decreasing and example, assume that an agency associates excellent increasing condition indicators for the do-nothing case.