Georgia achieved its goal of comparing competing alternatives by dedicating months of staff time to the development of customized spreadsheets that incorporate FHWA methodology to conduct an LCCA. The LCCA data is input into a decision matrix that was outlined in the 1993 version of the AASHTO Guide for Design of Pavement Structures for both a 30- and a 40-year analysis period. The result? An LCCA summary report that details the ranking for each alternative based on the following factors:
Based on plans submitted by the highway design section, the Office of Materials and Research first develops different pavement designs, e.g., hot-mix-asphalt (HMA), continuously reinforced concrete (CRC), full depth replacement, etc., that are applicable to the subject project. GDOT uses the parameters of the proposed pavement sections as inputs into a customized costing spreadsheet to calculate the total initial cost of each alternative. The base values for the cost data from the Engineering Services Office are loaded into the spreadsheet.
The next step is to establish the preservation and rehabilitation activity timing for each alternative. GDOT currently uses a 10-year activity cycle for HMA, 20 for Portland Cement Concrete (PCC), and 25 for CRC. These values are reduced by 20 percent in the LCCA, a recommendation from the FHWA Georgia Division Office for overlay alternatives. Once this information is input into the custom LCCA spreadsheet, the life-cycle costs associated with preservation and rehabilitation activities and the differential costs incurred by roadway users as they traverse these work zones are calculated. GDOT computes the present and annualized value of these costs using a discount rate of three percent. Since the agency costs and user costs are different costing streams, GDOT does not combine them; instead, it incorporates the calculated user costs in the weighted decision matrix to understand their influence.
Finally, GDOT inputs the LCCA agency cost results into the custom decision matrix spreadsheet, which assigns weights to each alternative based on its ability to meet the criteria in the categories listed above. The results are reviewed, and a recommendation is made to the highway design division.
Developing the customized LCCA, costing and decision matrix spreadsheets required extensive hours of work by Turner, who alone retains the knowledge required to generate an LCCA using the complex formulas and numerous macros for the various worksheets. GDOT recognizes that adopting the FHWA RealCost software would provide a tool usable by all practitioners and allow engineers to concentrate on applying engineering principles rather than on developing applications.
Figure 4: The user costs analysis input sheet, one of numerous customized spreadsheets developed by GDOT to conduct an LCCA