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71 Table 3.28. Recommended Time Periods for Constructing Pavement Preservation Treatments in Colorado Asphalt Pavement Treatments Application Timinga Concrete Pavement Treatments Application Timinga Crack filling Early fall Crack sealing Early fall Crack sealing Sand seals Elev 10,000 ft: 7/4 to 8/1 Joint resealing -- Chip seals 8,000 Elev < 10,000 ft: 6/15 to 8/15 Diamond grinding Microsurfacing 6,000 Elev < 8,000 ft: 6/1 to 9/1 Partial-depth repair 4,000 Elev < 6,000 ft: 5/15 to 9/1 Dowel bar retrofitting Elev < 4,000 ft: 5/1 to 9/1 Full-depth repair Ultra-thin bonded wearing course -- Thin HMAOL Mill and thin HMAOL Source: Galehouse 2004. Notes: HMAOL = Hot-mix asphalt overlay; 1 ft = 0.305 m. a Exclusive of weather limitations placed on treatments. Selection of the Preferred that are assumed to provide similar benefit (for example, a Preservation Treatment chip seal and a slurry that are both applied to improve surface texture). The second approach, BCR, requires much more data Cost is an important consideration in treatment selec- and computational effort and measures cost-effectiveness in tion. While the cost of a treatment does not have a direct the long term. It is appropriate for evaluating treatments that bearing on the effectiveness of a treatment, costs are an do not necessarily provide the same benefit, such as crack obvious consideration in what an agency can afford. How- sealing and a chip seal. ever, agencies are strongly encouraged to look beyond the Each approach requires reliable, up-to-date estimates of first costs or treatment initial construction costs and instead the cost and performance of the treatments to be analyzed. consider both the life-cycle costs and the benefit of the Historical bid prices are an excellent source for developing treatment. Approaches for doing this are described in greater treatment cost estimates, but these data must be adjusted to detail here. current-day values to account for the effects of inflation. To the extent possible, care should be exercised in developing Treatment Cost-Effectiveness Analysis estimated costs so that they account for project-specific factors, such as size (quantity of treatment needed), site-specific surface Cost-effectiveness analysis is an economic evaluation technique preparation requirements (such as material removal, patching, for comparing that which is sacrificed (cost) to that which is and cleaning), special traffic control requirements, and various gained (performance benefit) for the purpose of evaluating contingencies (e.g., striping and pavement marker removal alternatives (Lamptey et al. 2005). Cost-effectiveness can be and replacement and associated shoulder work), that may have measured in the short term (i.e., for one or more treatments affected the documented treatment costs. Also, to ensure a fair administered at a given time) or in the long term (i.e., for sev- cost comparison of all treatment options, the final estimated eral treatments carried out over an extended period of time) costs should be based on a common unit of measure, such as using analysis procedures that range from detailed and com- $/yd2 ($/m2) or $/lane-mi ($/lane-km). plex to less detailed and simple. In simple terms, the alterna- Obtaining meaningful estimates of treatment performance tive that provides the greatest benefits for the least costs is is more complicated. Ideally, these are developed using data the "best." from the PMS database and the pavement history database This section presents two approaches that can be used to (if separate from the PMS database) and, more recently, from evaluate the cost-effectiveness of preservation treatments. maintenance management systems. However, very few PMS These approaches are the equivalent annual cost (EAC) and the databases include information on preservation treatment benefit-cost ratio (BCR). EAC is simpler to conduct and requires performance or are able to discern the issue of greatest interest: only basic information regarding cost and performance. It when the treatment stopped being effective. In any analysis of measures cost-effectiveness in the short term for alternatives available data, care should be taken to ensure that the data
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72 analyzed are from projects with characteristics (e.g., existing In this analysis method, the expected treatment performance pavement type and conditions, traffic loadings, and climatic is the extension in service life of the pavement generated by the conditions) that are similar to those of the proposed project. preservation treatment. Although this extension may be easily This is sometimes referred to as the "pavement family" concept. identified as (a) the time taken for the pavement condition or Although pavement survival analysis techniques (i.e., time serviceability/smoothness to return to the level it was at imme- until treatment failure or until a specific threshold condition diately prior to the treatment, a more discerning appraisal is reached) can be used, estimates of treatment performance uses (b) the difference between the time taken for the treated are more easily achieved using pavement performance mod- pavement to deteriorate to a certain threshold level and the time eling techniques (i.e., time-series trends of overall condition, taken for the untreated pavement to deteriorate to the same serviceability, and individual distress development). And, since threshold level. Both approaches are illustrated in Figure 3.11. pretreatment pavement condition can have a significant impact on treatment life, the analysis should be limited to projects Benefit-Cost Ratio with pretreatment condition levels that are similar to the proposed project. The BCR method of cost-effectiveness combines the results If historical performance data are not available or are of individual evaluations of treatment benefits and treat- insufficient for analysis, then performance information should ment costs to generate a benefit-to-cost (B/C) ratio. The B/C be sought from other sources. These may include agencies ratios of alternative preservation treatments (and, if desired, that have utilized the candidate treatments in similar condi- a "no treatment" option) are then compared and the treatment tions or from practitioners knowledgeable of the performance with the highest ratio is deemed the most cost-effective. Since of the candidate treatments. the analysis is performed over a long period covering the life cycle of a pavement, the costs and performance characteristics of the existing pavement (whether the original structure or Equivalent Annual Cost the last significant rehabilitation treatment) and all future The EAC method of cost-effectiveness is an inverse measure projected preservation and rehabilitation treatments associ- of the "bang for the buck" concept. It involves a simple cal- ated with a given preservation strategy must be estimated. culation of the treatment unit cost (inclusive of supplemental In the BCR method, the benefits associated with a particular preparation work and maintenance of traffic) divided by the preservation strategy are evaluated from the standpoint of expected treatment performance, as shown in Equation 1. benefits accrued to the highway user over a selected analysis period (usually 25 to 40 years, beginning from the original Treatment Unit Cost construction). They are quantified by computing the area EAC = (1) Expected Performance, years under the pavement performance curve, which is defined by Approach A: Life Pavement extension based on Condition pretreatment condition levels Preservation Treatment Condition Threshold Approach B: Life extension based on specified condition threshold levels Time, years Figure 3.11. Estimation of preservation treatment life.
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73 Pavement Total Benefit = B0 + BP1 + BOL1 + BOL2 Condition New Pavement Construction Preservation Overlay 1 Overlay 2 Treatment 1 B0 BP1 BOL1 BOL2 Lower Benefit Limit Time, years Analysis Period C0 COL1 COL2 CP1 S Figure 3.12. Illustration of benefits and costs associated with a pavement preservation treatment strategy. the expected timings of future preservation and rehabilitation where treatments and the corresponding jumps and subsequent NPV = Net present value, $; deterioration in condition or serviceability/smoothness. The IC = Present cost of initial construction activity, $; expected timings are determined from service life analyses of k = Number of future preservation/rehabilitation the existing pavement and the specific rehabilitation treat- activities; ments, and from the service life extensions estimated for the M&Rj = Cost of jth future preservation/rehabilitation preservation treatment. The top portion of Figure 3.12 illustrates the assessment activity in terms of present costs (i.e., constant/ of benefits using the area-under-the-performance-curve real dollars), $; approach. A treatment alternative with more area under the idis = Discount rate; curve yields greater benefit through higher levels of condition nj = Number of years from the present of the jth future or serviceability/smoothness provided to the highway users. M&R activity; The costs associated with a particular preservation strategy SV = Salvage value, $; and are evaluated using life-cycle cost analysis (LCCA) techniques. AP = Analysis period length, years. The LCCA must use the same analysis period and the same The bottom portion of Figure 3.12 illustrates the stream of timings of preservation and rehabilitation treatments as those costs included in the LCCA. These costs occur in accordance used previously in computing benefits. A specified discount with the preservation and rehabilitation treatment timings rate (typically 3% to 5%) is used to convert the costs of the established and used in the analysis of benefits. They represent future projected preservation and rehabilitation treatments the costs paid by the agency to construct the existing pavement (and any salvage value at the end of the analysis period) to and apply the subsequent preservation and rehabilitation present-day costs. These costs are then summed together with treatments. the cost of the existing pavement (again, either the original Although most state highway agencies have a standardized structure or the last significant rehabilitation) to generate the procedure for conducting LCCA, state-of-the-practice guidance total life-cycle cost (expressed as net present value [NPV]) has been developed and made available by the FHWA through associated with the preservation strategy. The computational the Interim Technical Bulletin on LCCA in Pavement Design formula used in this process is shown in Equation 2. (Walls and Smith 1998). A companion LCCA spreadsheet n AP program, RealCost, has also been developed and is available k 1 j 1 NPV = IC + M & R j × - SV × 1 + i (2) for public use at www.fhwa.dot.gov/infrastructure/asstmgmt/ j =1 1 + idis dis lccasoft.cfm.
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74 In the final step of the BCR method, the B/C ratio for each this cost (5% to 10%) may be added to reflect the engineering preservation strategy is computed by dividing the "benefit" (design and construction), administrative, and traffic control obtained from the area-under-the-performance-curve analysis costs anticipated with the treatment's construction. by the "cost" obtained from the LCCA: Treatment unit costs depend on several factors, the most notable of which include the size and location of the project, B C = Benefit NPV (3) severity and quantity of distresses, and the quality of a treat- ment's constituent materials. In this study, unit cost infor- As stated previously, the treatment with the highest B/C mation was gleaned from the literature to serve as a general ratio is deemed the most cost-effective. resource in the absence of agency estimates derived from historical bid tabulations. Tables 3.29 and 3.30 show the unit costs obtained for treatments applied to HMA- and PCC- Treatment Costs surfaced roadways, respectively, along with a relative cost Although treatment costs do not affect treatment perfor- indicator. The costs represent the in-place costs of the treat- mance, certain cost considerations are inevitably a crucial ments, exclusive of traffic control costs and any associated part of the treatment selection process. The costs of interest surface preparation costs. are (a) the direct costs incurred by the highway agency as a The use of these relative or comparative costs is introduced result of constructing the treatment and (b) the indirect costs because the recent volatility of materials prices, as well as borne by the highway users as a result of the disruptions created variations in prices by region, project location, contractor by treatment construction work zones. availability, project size, and so on highlight the perils of report- ing costs that will most certainly change. What is less likely to DIRECT AGENCY COSTS change is the comparative relationship between these costs, The direct agency costs primarily consist of the in-place cost although even that is not an absolute. of the treatment (typically, the product of the awarded con- tractor's unit cost for the treatment and the estimated treatment INDIRECT USER COSTS quantity, supplemented by surface preparation costs and main- User costs are defined as nonagency costs that are borne by tenance of traffic costs). In some instances, a percentage of the users of a pavement facility (Peshkin et al. 2004). User Table 3.29. Estimated and Relative Treatment Costs for Preservation Treatments on HMA-Surfaced Pavements Treatment Relative Cost ($ to $$$$) Estimated Unit Cost Crack filling $ $0.10 to $1.20/ft Crack sealing $ $0.75 to $1.50/ft Slurry seal $$ $0.75 to $1.00/yd2 Microsurfacing (single course) $$ $1.50 to $3.00/yd2 Chip seal (single course) $$ (conventional) $1.50 to $2.00/yd2 (conventional) $$$ (polymer modified) $2.00 to $4.00/yd2 (polymer modified) Ultra-thin bonded wearing course $$$ $4.00 to $6.00/yd2 Thin HMA overlay (dense graded) $$$ $3.00 to $6.00/yd2 Cold milling and thin HMA overlay $$$ $5.00 to $10.00/yd2 Ultra-thin HMA overlay $$ $2.00 to $3.00/yd2 Hot in-place recycling (excluding thin HMA overlay $$/$$$ $2.00 to $7.00/yd2 for surface recycle and remixing types) Cold in-place recycling (excluding thin HMA overlay) $$ $1.25 to $3.00/yd2 Profile milling $ $0.35 to $0.75/yd2 Ultra-thin whitetopping $$$$ $15.00 to $25.00/yd2 Note: $ = low cost; $$ = moderate cost; $$$ = high cost; $$$$ = very high cost.
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75 Table 3.30. Estimated and Relative Treatment Costs for Preservation Treatments on PCC-Surfaced Pavements Treatment Relative Cost ($ to $$$$) Estimated Unit Cost Joint resealing $ $1.00 to $2.50/ft Crack sealing $ $0.75 to $2.00/ft Diamond grinding $$ $1.75 to $5.50/yd2 Diamond grooving $$ $1.25 to $3.00/yd2 Partial-depth patching $$/$$$ $75 to $150/yd2 (patched area) (equivalent $2.25 to $4.50/yd2, based on 3% surface area patched) Full-depth patching $$/$$$ $75 to $150/yd2 (patched area) (equivalent $2.25 to $4.50/yd2, based on 3% surface area patched) Dowel bar retrofit $$$ $25 to $35/bar (equivalent $3.75 to $5.25/yd2, based on 6 bars per 12-ft crack/ joint and crack/joint retrofits every 30 ft) Ultra-thin bonded wearing course $$$ $4.00 to $6.00/yd2 Thin HMA overlay $$$ $3.00 to $6.00/yd2 Note: $ = low cost; $$ = moderate cost; $$$ = high cost; $$$$ = very high cost. costs are incurred through various mechanisms and at any A work zone is defined as an area of a highway where main- time over the life of a project. Overall, there are five primary tenance, rehabilitation, or construction operations are taking mechanisms of user costs: place that impinge on the number of lanes available to moving traffic or affect the operational characteristics of · Time-delay costs. Opportunity costs incurred as a result of traffic flowing through the area (Walls and Smith 1998). additional time spent completing a journey because of work A work zone disrupts normal traffic flow, drastically zones (i.e., lane restrictions, road closures) associated with reduces the capacity of the roadway, and leads to specific construction, maintenance, or rehabilitation activities. The changes in roadway use patterns that affect the nature of opportunity cost represents the value associated with other user costs. activities that cannot be completed because of the extra · Normal operating condition costs. In between work zone time that is normally spent completing a journey. periods, user costs are still incurred during normal operating · Vehicle operating costs (VOCs). Costs associated with fuel conditions. These include highway user costs associated with and oil consumption, tire wear, emissions, maintenance using a facility during periods free of construction, repair, and repair, and depreciation due to work zone traffic flow rehabilitation, or any work zone activity that restricts the disruptions or significantly rough roads. VOCs typically capacity of the facility. involve the out-of-pocket expenses associated with owning, operating, and maintaining a vehicle. The inclusion of user costs as part of any economic analysis · Crash costs. Costs associated with additional crashes brought of pavements is a controversial issue. Less than a quarter of about by work zones or by rough or slippery roads. Crash the survey respondents reported that they account for user costs are primarily composed of the costs of human fatalities, costs when evaluating preservation treatments. However, on nonfatal injuries, and accompanying property damage. high-traffic-volume roadways, user costs can represent a · Discomfort costs. Costs associated with driving in congested significant portion of the total cost. traffic or on rough roads. Current FHWA-recommended practice is to consider · Environmental costs. Costs associated with traffic noise and including in the economic analysis only the time-delay and with the operation of work zone construction equipment. VOC components associated with work zones. These com- ponents can be estimated reasonably well and make up a large Additionally, user costs can be incurred during the estab- portion of the total user costs. Other work zone user cost lishment of a work zone or during normal (nonrestricted) components are either too difficult to collect and reasonably highway operating conditions: quantify or do not factor to an appreciable amount. Further, for most pavement facilities in fair or good condition (e.g., pave- · Work zone costs. This category of user costs deals with ments with a PSR of 2.5 or greater), user costs during normal costs brought about by the establishment of a work zone. operating conditions are minimal (Peshkin et al. 2004).
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76 For projects in which time-delay and VOC user costs are · The second aspect is the work zone user costs associated likely to occur as a result of performing preservation or reha- with the timing of an assumed future rehabilitation at bilitation activities, consideration should be given to evaluating the end of the preservation treatment's expected life. A these costs as part of the selected cost-effectiveness analysis preservation treatment with a longer forecasted life results method. Detailed procedures for computing them are provided in a delay in the timing of the assumed rehabilitation. in the FHWA's Interim Technical Bulletin on LCCA in Pavement When discounted to present-day costs, the work zone user Design (Walls and Smith 1998), and the RealCost spreadsheet costs associated with the rehabilitation will be lower than program can be used to perform the computations. A some- the same rehabilitation work zone user costs associated what simplified approach for computing work zone time-delay with a shorter-life preservation treatment. This is illustrated costs is presented in NCHRP Report 523 (Peshkin et al. 2004). in Figure 3.13. The OPTime spreadsheet program developed as part of that · In the BCR method, the user costs of all future preservation study on optimal timing of PM can be used to perform the and rehabilitation treatments associated with each preser- computations. The following are brief descriptions of how vation strategy can be computed as part of the LCCA. Al- user costs can be incorporated into the EAC and BCR methods though the user cost NPV results may be combined with the of cost-effectiveness analysis: agency cost NPV results, it is generally recommended that they be examined separately because of the possibility that · In the EAC method, two aspects of user costs can be con- they will overwhelm the agency costs. sidered. The first aspect is the work zone user costs asso- ciated with each alternative preservation treatment. Since Evaluation of Economic the work zone characteristics of each alternative will vary and Noneconomic Factors based on application rates, material setting and curing times, and other construction factors, the delays experi- Although treatment cost-effectiveness is a major consideration enced as a result of the different work zone requirements in the selection of the preferred treatment, it is not the final will also vary. answer in the process. The reality of the decision process is Pavement Condition Preservation Treatment 1 (PT1) Preservation Treatment 2 (PT2) Condition Threshold (Trigger for Rehabilitation) LifePT2 LifePT1 Time, years UCRehab UCRehab Discount future UCRehab user costs to NPV present day (PT2) UCRehab NPV (PT1) TPT2 TPT1 Time, years Figure 3.13. Effect of preservation treatment life on discounted rehabilitation user costs.
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77 that many other factors (economic and noneconomic) must be summed and compared with the weighted scores of the other considered along with cost-effectiveness. Some of these factors treatments. The treatment with the highest score is then may have been previously considered as part of the steps to recognized as the preferred treatment. identify feasible treatments, yet may also be desired for consid- A fairly complete list of factors that are appropriate for eration in the final selection. Examples include the availability inclusion in the final selection process follows. The factors are of qualified (and properly equipped) contractors and quality grouped according to different attributes, which can also be materials, the anticipated level of traffic disruption, and surface assigned weights as part of a decision matrix: characteristics issues. Upon completion of the cost-effectiveness analysis, it may · Economic attributes: be desirable to eliminate certain treatment alternatives on the Initial cost; basis of not being able to meet key financial goals. Such elim- Cost-effectiveness (EAC or BCR); ination criteria might include the following: Agency cost; and User cost. · Substantially lower cost-effectiveness compared with other · Construction/materials attributes: treatment alternatives (e.g., EAC greater than 10% higher Availability of qualified (and properly equipped) con- than the EACs of the alternatives, B/C ratios greater than tractors; 10% less than the ratios of the alternatives); Availability of quality materials; · Initial cost greater than available funding, resulting in Conservation of materials/energy; and negative impact on network-level budgeting; and Weather limitations. · Excessive user costs that would have serious negative impact · Customer satisfaction attributes: on roadway users. Traffic disruption; Safety issues (friction, splash/spray, reflectivity/visibility); Alternatively, these economic factors can be combined with and several noneconomic factors, as described below. Ride quality and noise issues. A useful mechanism to systematically and rationally eval- · Agency policy/preference attributes: uate the different factors and identify the preferred treatment Continuity of adjacent pavements; is a treatment decision matrix. In a treatment decision matrix, Continuity of adjacent lanes; and various selection factors are identified for consideration and Local preference. each factor is assigned a weight. The weights are then multi- plied by rating scores given to each treatment alternative, based A decision matrix that incorporates these factors and illus- on how well the treatment satisfies each of the selection factors. trates the assignment of weights and the basis for rating scores The weighted scores of each treatment alternative are then is provided in Table 3.31.
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78 Table 3.31. Example of Preservation Treatment Decision Matrix Treatment 1 Treatment 2 Attribute Factor Combined Rating Weighted Rating Weighted Attribute and Selection Factor Weight Weight Weight Score Score Score Score Economic 40 Initial cost 30 12.0 Cost-effectiveness 30 12.0 Agency cost 10 4.0 User cost 30 12.0 Total 100 Construction/materials 25 Availability of qualified contractors 20 5.0 Availability of quality materials 20 5.0 Conservation of materials/energy 30 7.5 Weather limitations 30 7.5 Total 100 Customer satisfaction 25 Traffic disruption 40 10.0 Safety issues 40 10.0 Ride quality and noise issues 20 5.0 Total 100 Agency policy/preference 10 Continuity of adjacent pavements 20 2.0 Continuity of adjacent lanes 20 2.0 Local preference 60 6.0 Total 100 Cumulative Weighted Score Note: Basis for treatment rating scores (1-to-5 scale); initial cost: 1 = highest, 5=lowest; cost-effectiveness: 1 = least cost effective, 5 = most cost-effective; agency cost: 1 = highest, 5 = lowest; user cost: 1 = highest, 5 = lowest; availability of qualified contractors: 1 = low/none, 5 = high; availability of quality materials: 1 = low/none, 5 = high; conservation of materials/energy: 1 = low, 5 = high; weather limitations: 1 = major, 5 = low/none; traffic disruption: 1 = major, 5 = low/none; safety issues: 1 = serious, 5 = none; ride quality and noise issues: 1 = serious, 5 = none; continuity of adjacent pavements: 1 = does not match at either end, 5 = matches at both ends; continuity of adjacent lanes: 1 = does not match, 5 = matches; local preference: 1 = inconsistent with preference, 5 = consistent with preference.