RealCost data needs are identical to the data needs of the FHWA's best practice LCCA process. When the data have been entered, the software performs the required calculations to produce life-cycle costs. Furthermore, the software permits the analyst to quickly consider natural modifications to the data that result from analysis of earlier LCCA iterations. The LCCA steps and their corresponding data entry and output forms are listed in Table 2.
|FHWA LCCA Steps||RealCost Data Entry and Output Forms|
|1. Establish Design Alternatives||Project Details
Traffic Hourly Distribution
Value of User Time
Added Vehicle Time and Cost
|2. Determine Activity Timing||Alternative 1 and Alternative 2|
|3. Estimate Agency and User Costs||Alternative 1 and Alternative 2|
|4. Compute Life-Cycle Costs||Deterministic Results
|5. Analyze the Results||Deterministic Results
The LCCA process requires two levels of information: 1) data pertaining to the proposed pavement project and 2) data defining the pavement design alternatives that are being compared for accomplishing the project.
Project-level data apply to all alternatives being considered for the project at hand. FHWA's best practice LCCA methodology requires that the analysis period, discount rate, normal operations traffic data, and normal operations roadway geometry be the same for all alternatives. Alternative-level data define the differences between project alternatives (e.g., agency costs and work zone specifics for each alternative's component activities).
In comparisons of alternative designs intended to similarly fulfill the performance requirements of a project, LCCA requires that each alternative carry the same amount of traffic during normal operations throughout the life of the project. In this way, the benefits to road users provided by all alternatives are the same. The exception to this rule is during periods of work zone operations, when traffic flow may be restricted in some fashion. Work zone traffic flow restrictions are modeled by RealCost with the user cost methodology described in the FHWA technical bulletin Life-Cycle Cost Analysis in Pavement Design.
To emphasize the difference between the two types of inputs, RealCost requires that project-level data be entered separately from alternative-level data. Figure 10 illustrates the division between project-level and alternative-level data.
Figure 10. The hierarchy of project-level and alternative-level data.
The options selected and data entered in the project-level data input forms apply to all alternatives being considered to fulfill the performance requirements of the single project. If the project-level data or options are changed, all alternatives must be reconsidered with the new data and options in order to be properly compared. Alternatives analyzed using different project-level options cannot be directly compared in LCCA.
The Project Details form (Figure 11) is used to identify and document the project. Data entered into this form are not used in the analysis. The analyst may enter data according to the field names on the form or may use the fields to include other project documentation details.
Figure 11. Project Details form.
Generally, analysis options are decided by agency policy rather than the pavement design decisionmaker. Options defined in the Analysis Options form include the analysis period, discount rate, beginning year, inclusion of residual service life, and the treatment of user costs in the LCCA (see Figure 12). A checked box equals "yes," an unchecked box equals "no." The data inputs and analysis options available on this form are discussed in Table 3, with FHWA's recommendations.
Figure 12. Analysis Options form.
|Analysis Period||The number of years over which the alternatives will be compared.||35 to 40 years|
|Discount Rate||The rate by which future expenditures will be discounted to present value. This is entered as a decimal number.||Real discount rate of 3% to 5%|
|Beginning of Analysis Period||Sets the first year of the analysis period. RealCost expenditure diagrams draw their dates from this field and the analysis period field. This can also be referred to as the base year for the analysis.||Year the project will be undertaken|
|Include Agency Cost Remaining Service Life||Indicates whether the remaining service life value will include a prorated share of agency costs if the service life of an improvement extends beyond the analysis period.||Checked (Yes)|
|Include User Costs in Analysis||Indicates whether user costs will be included in the analysis and displayed in the results.||Checked (Yes)|
|User Cost Computation Method||Directs RealCost to either 1) calculate user costs ("Calculated") based upon input data in accordance to best practice methods or 2) utilize inputted user costs ("Specified") values when calculating user life-cycle costs.||Calculated|
|Traffic Direction||Directs RealCost to calculate user costs for the "inbound" lanes, the "outbound" lanes, or "both" inbound and outbound lanes.
|Include User Cost Remaining Service Life||Indicates whether the remaining service life value will include a prorated share of user costs if the service life of an improvement extends beyond the end of the analysis period.||Checked (Yes)|
Pavement engineers use traffic data to determine their design parameters. In RealCost, traffic data (Figure 13) are used exclusively to calculate work zone user costs in accordance with the method outlined in FHWA's LCCA Technical Bulletin. The traffic data inputs are described in Table 4.
Figure 13. Traffic Data form.
|AADT in Both Directions||This is the annual average daily traffic in the construction or base year of the analysis. This is the total AADT for both directions.|
|Single Unit Trucks||The percentage of the AADT that is single unit trucks.|
|Combo Trucks||The percentage of the AADT that is combination trucks.|
|Annual Growth Rate of Traffic||The percentage by which "AADT in both directions" increases each year.|
|Normal Operations Speed Limit||Speed limit in normal operating conditions (the time periods between agency work zones).|
|Normal Number of Lanes Open||Number of roadway lanes available under normal operating conditions.|
|Queue Dissipation Capacity||Capacity of each lane during queue dissipation operating conditions.|
|Normal Free Flow Capacity||Capacity of each lane under normal operating conditions.|
|Free Flow Capacity Calculator||This button opens a form that calculates free flow lane capacities based upon the Highway Capacity Manual, 3rd Ed.|
|Maximum AADT in both Directions||Caps the traffic growth at this number. If traffic grows beyond this value, this value is substituted for the computed future AADT figure and future user costs are calculated based upon this maximum AADT figure. This is used to prevent growth beyond possible capacity.|
|Maximum Queue Length||Models the effects of self-imposed detours (traffic exiting from the work zone route yet still incurring some user costs). Queue-related user costs, which are based upon queue length, are calculated with this figure instead of the calculated queue length. However, all vehicles, even those that detour, are charged queue costs.|
|Rural or Urban Traffic||Allows the choice between two hourly traffic distributions. Default values for these distributions (the defaults are accessible in the software) are taken from the Texas Transportation Institute's MicroBENCOST.|
The Value of User Time form, shown in Figure 14, allows editing of the values applied to an hour of user time. The dollar value of user time is different for each vehicle type and is used to calculate user costs associated with delay during work zone operations.
Figure 14. Value of User Time form.
To transform annual average daily traffic (AADT) to an hourly traffic distribution, default Rural and Urban Traffic hourly distributions from MicroBENCOST are provided with RealCost. The Traffic Hourly Distribution form (Figure 15 and Table 5) is used to adjust (or restore) these settings. Distributions are required to sum to 100 percent. (Note: The rural/urban option is entered on the Traffic Data form, shown in Figure 13.)
Figure 15. Traffic Hourly Distribution form.
|AADT Rural %||The percentage of the AADT that is traveling on the roadway, in both directions, during the indicated hour under the rural traffic distribution.|
|Inbound Rural %||The percentage of that hour's traffic that is traveling inbound on the route under the rural traffic distribution. The formula:
(AADT Rural %) x (Inbound Rural %)
describes the percentage of the AADT traveling in the inbound direction for the indicated hour.
Note: The same interpretations apply to the urban components of Figure 15.
|Restore Defaults||Returns all values on this form to their original, as delivered, default values. Default values for these distributions are taken from MicroBENCOST, software produced by the Texas Transportation Institute. MicroBENCOST, which is used to calculate benefits and costs of transportation improvements, includes an hourly traffic distribution that has been adopted as a default traffic distribution for RealCost.|
"Added Time per 1,000 Stops (Hours)" and "Added Cost per 1,000 Stops ($)" values are used to calculate user delay and vehicle costs due to speed changes that occur during work zone operations. This form (Figure 16) is used to adjust the default values for added time and added cost per 1,000 stops. The "Idling Cost per Veh-Hr ($)" is used to calculate the additional vehicle operating costs that result from traversing a traffic queue under stop and go conditions. The costs and times are different for each vehicle type.
The Restore Defaults button functions much the same as it does on the Traffic Hourly Distribution form. The default values are drawn from NCHRP Study 133, Procedures for Estimating Highway User Costs, Air Pollution, and Noise Effects.
Figure 16. Added Time and Vehicle Stopping Costs form.