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21 in the following subsection are needed to determine appro- related user delay costs, and other routine maintenance costs. priate weighting factors. The user can select one or more of these available cost types to include in an analysis. The details associated with each of Trials of Different Combinations of Benefit Weighting these cost types are described as follows. Factors. Useful feedback may be obtained by conducting a series of analyses in which different combinations of weight- ing factors are investigated. For example, the selection of ini- Treatment Costs tial weighting factors as the baseline (e.g., 60 for rutting, 30 for cracking, and 10 for friction) indicates that controlling rutting Treatment costs include all agency costs associated with appears to be the most important purpose of the treatment, and the placement of a preventive maintenance treatment. These the overall optimal timing is thus likely to be closer to the age include design, mobilization, materials, construction, and traf- fic control costs. Although the analysis methodology allows associated with the individual analysis in which only rutting these costs to be omitted, it is highly recommended that treat- was considered (i.e., 4 years) than to the ages associated with ment costs be included in any analysis. the other condition indicators (i.e., 2 or 7 years). Conducting a simplified sensitivity analysis of different combinations of benefit weighting factors should provide Rehabilitation Costs information to support the initial choices for weighting fac- tors or to help make appropriate changes to the individual Because the application of preventive maintenance is factors. Continuing with the example above, assume that the expected to prolong the need for major rehabilitation, the results summarized in Table 17 are obtained by conducting a inclusion of rehabilitation costs is an option in the analysis series of targeted analyses. A simultaneous interpretation of approach. As the cost of a required rehabilitation activity can such "what if" scenario results--combined with the optimal be large in relation to the cost of a preventive maintenance timings estimated by conducting the separate condition indi- treatment, the timing of the expected rehabilitation activity cator analyses--should provide a good indication of the ben- can have a significant impact on a pavement's overall life- efit weighting factors that are best for a specific analysis. cycle cost (LCC). Because the process for determining appropriate benefit weighting factors is very similar to that used by agencies to develop composite distress indices, many agencies may already Work Zone-Related User Delay Costs have processes that can be adapted. Regardless of the method used to select the weighting factors, it is recommended that The methodology considers only user costs associated with an agency regularly review the selected factors whenever work zone delays (i.e., the cumulative delay cost recognized additional (or more accurate) performance data become avail- by all users subjected to the work zone during construction able (i.e., whenever performance relationships are updated). of the treatment). This approach favors treatments that pro- This review will greatly increase the chances of obtaining vide some benefit but can be placed comparatively quickly more accurate analysis results. with little disruption to the traveling public. The methodology does not include other common types of condition-sensitive user costs (e.g., vehicle operating costs, discomfort, and acci- Cost Considerations dent costs) because the difference in pavement condition for preventive maintenance candidates is expected to be rela- The second fundamental aspect of the proposed method- tively small. ology is the inclusion of costs that are impacted by the appli- The cumulative delay cost is computed as a function of the cation of preventive maintenance activities. The current meth- average number of vehicles per day (AADT), work zone dura- odology allows the user to consider preventive maintenance tion, average vehicle delay time, and cost per delay time per treatment costs (agency costs), rehabilitation costs, work zone- vehicle. TABLE 17 Example of optimal timings resulting from conducting a series of analysis sessions with different benefit weighting factors Rutting Cracking Friction Resulting Estimated Weighting Factor Weighting Factor Weighting Factor Optimal Timing, age 60 30 10 5 60 25 15 6 60 35 5 4 70 20 10 4 50 40 10 3

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22 In general terms, user costs are defined as non-agency General project inputs (e.g., project length, number of costs that are borne by the users of a pavement facility, and lanes); typically consist of the following: Traffic data (e.g., 2-way average daily traffic [ADT], directional split, hourly traffic distribution); Vehicle operating costs (VOC)--Costs induced because Work zone closure data (e.g., time period(s) in which the of increased wear and tear on a vehicle when using a closure is in place, duration of the work zone closure, pavement (because of stopping/starting or excessive number of available lanes, posted and work zone speed pavement roughness) during normal operations. Normal limits, vehicle capacity, queue dissipation rates); and operations are periods in which a pavement facility is Value of time delay costs (for passenger, single unit, free of construction, maintenance, or rehabilitation activ- and commercial vehicles). ities that would otherwise affect the capacity. Costs in this category are generally related to pavement rough- With these inputs, the movement of vehicles through the work ness, and therefore do not begin to accrue until after the zone can be analyzed, yielding information on user delay pavement has reached a higher level of roughness (e.g., times (including delays because of the possible development an IRI of about 2.7 m/km [170 in./mi], or a present ser- of queues) which can be converted to user delay costs. The viceability rating [PSR] of about 2.5). analysis can be conducted by several computer programs User delay costs--Additional costs caused by time delays (e.g., MicroBENCOST, QueWZ). It is somewhat complex in traveling over a pavement facility as a result of the and requires inputs that may not be readily available for the following: analysis of most projects. Consequently, a more simplified Reduced speed to enter the work zone (or even a com- procedure is needed for this methodology. plete stop, if there is queuing), To include user costs in the analysis, an easy method is Reduced speed through the work zone; and needed to compute the time delays for vehicles traveling Use of alternate routes to avoid the work zone. through the work zone. If this value is estimated, then the Crash costs--Costs associated with fatalities or injuries entire calculation process becomes straightforward. Table 18 that result from crashes on a pavement facility. lays out the calculation routine for the incorporation of user delay costs, with each of the columns in that table defined The inclusion of user costs as part of a life-cycle cost analy- following the table. sis (LCCA) is a controversial issue. While there is general agreement that traffic delays increase user costs, the actual Column A: The classification of vehicles using the costs are difficult to quantify and they are not costs borne facility (the 1998 FHWA report recommends just three directly by the highway agency. When user costs are included classes: passenger cars, single-unit trucks, combination in an analysis, they often overwhelm the direct agency costs, trucks) (23). particularly for high-volume facilities. Some highway agen- Column B: The approximate number of vehicles in each cies choose not to include user costs in an LCCA while oth- of three categories that are affected by the work zone; ers choose to compute direct costs and user costs separately this is largely influenced by the length of time that the and include user costs as an additional evaluation criteria work zone is in place (if the work zone is periodic, then when evaluating competing construction bids (often referred it is the vehicles that pass through the zone only during to as A + B contracts). that period). For most pavement facilities in fair or good condition Column C: The delay cost rate for each vehicle classifica- (e.g., pavements with a PSR of 2.5 or greater), user costs dur- tion (ranges are provided in the 1998 FHWA report) (23). ing normal operations are minimal; consequently, the user Column D: The average additional delay time for each costs associated with the placement of work zones for pave- vehicle that is affected by the work zone. This value is ment maintenance or rehabilitation activities are of the great- estimated for each project, and is strongly related to the est concern in this project. Of the three types of user costs, physical length of the work zone, the number of lanes only user delay costs are incorporated into the optimal tim- that are closed (and the capacity of those that remain ing methodology because they are generally significantly open), and whether or not a queue is expected to form. larger than the vehicle operating costs or the crash costs; Column E: The total cost for each vehicle classification, there is a dearth of statistical data to support crash rates in which is the product of column B, column C, and col- work zones, and there is controversy associated with crash umn D (making sure all units are consistent). cost rates. This simplified process introduces several sources of error. Estimating User Delay Costs. The 1998 FHWA report, Life- One obvious source of error is the accuracy of the user's esti- Cycle Cost Analysis in Pavement Design (23), outlines the mates. Although these errors may be significant, these esti- steps for estimating work zone user delay costs. The process mates can be used to make meaningful comparisons of the requires at least the following information: relative effects. Another source of error arises if the work zone