Bridge over the Susquehanna River
In the mid 1980s, PennDOT initiated a policy requiring that LCCA be performed for all interstate highway projects with estimated initial costs of more than $1 million and for all other projects with estimated initial costs of more than $10 million. About 15 to 20 pavement projects each year are of sufficient scale to warrant an LCCA under this policy. PennDOT relies on agency life-cycle costs to make its pavement design selection; however, when the agency life-cycle costs of different alternatives are sufficiently close, the life-cycle costs to users are included in the analysis. All PennDOT pavement analyses are performed in accordance with LCCA procedures contained in the Pavement Policy Manual, PennDOT Publication 242, which also explains the pavement design procedure.
PennDOT stipulates that its principal routes be designed to produce 20 years of performance using the 1993 AASHTO Design Procedure. The inputs to this procedure-initial average daily traffic, anticipated traffic growth, desired performance period, and paving material characteristics- generally determine the required pavement design for any paving material.
Pavement designs, whether for initial road construction, adding capacity, or pavement rehabilitation projects, are performed by engineers at PennDOT's engineering districts. District office engineers design the pavement, investigate right-of-way requirements, and conduct environmental reviews. Additionally, these engineers must produce an LCCA for projects when required by policy. The selected project design and its supporting documentation, including the LCCA, are sent for review to the Pavement Design and Analysis Section of the Bureau of Maintenance and Operations at PennDOT's central office in Harrisburg. Project approval is contingent upon successfully passing the State-level review in all design areas, including determination of the long-term, least-cost alternative for projects where an LCCA is required.
If an LCCA is required, PennDOT pavement design selection guidelines require engineers to compare at least one bituminous and one Portland cement concrete design alternative for each project. All competing pavement alternative designs are compared over a 40-year analysis period (which accounts for the 20-year initial design standard and subsequent rehabilitation requirements). Each design alternative being considered must meet the performance requirements of the project throughout the analysis period. Accordingly, for each competing alternative, the design engineer must identify the initial construction activities as well as all future rehabilitation and maintenance activities that are needed to ensure the performance of the pavement. The result is a schedule for each alternative of when future maintenance and rehabilitation activities will occur, when agency funds will be expended, and when and for how long the agency will establish work zones.
The design engineer must then calculate the agency and user costs for these activities. Work zone user costs are calculated from the additional delay and vehicle operating costs due to the effects of work zones on roadway capacity. PennDOT has determined that as all alternatives will, by design, provide similar performance, the only quantified difference in user costs will be due to work zone effects.
Estimates of agency and user costs in an LCCA are developed in constant (i.e., real) dollars, which do not include an inflation component. For example, the same unit values for material, labor, and user time used to estimate the agency and user costs of an activity occurring in the first year of the analysis period would be used to estimate costs for every anticipated activity in the analysis period.
At this point, the total life-cycle agency and user costs of each alternative are calculated. However, dollars spent at different times have different values to the agency from the standpoint of the present day (e.g., $100 today has a greater present value than $100 made available 20 years from now). Therefore the projected activity costs for an alternative cannot simply be summed to calculate total life-cycle cost for that alternative. PennDOT uses economic methods (e.g., discounting) to convert anticipated future costs to present dollar values so that the total costs of different alternatives can be directly compared. PennDOT uses a real discount rate of 6 percent, which like the agency and user costs, excludes the effects of inflation. This discount rate has been derived from an average, long-term State bond rate with the inflation component removed. If the difference between the alternative with the least agency cost and all other alternatives is greater than 10 percent, the least-cost alternative is selected.
If the difference is less than 10 percent, another design, which does not have the least cost, may be chosen, and other factors are consulted in the selection. This selection process acknowledges that there is an element of uncertainty in LCCA results. The other factors considered are the user life-cycle costs, constructability considerations, and the performance of similar pavements in the same geographic area.
When the pavement design is completed, it is submitted by the district to the Design and Analysis Section at PennDOT's central office. After all aspects of the design are reviewed by this section and the LCCA results are verified, the pavement design is approved.
Schuylkill Expressway, southwest Philadelphia
|PennDOT standardized all pavement design processes, including LCCA, in two manuals: Highway Geometric Design Manual and Pavement Policy Manual.|
LCCA is data-intensive. It specifically requires cost and performance data for construction and rehabilitation activities. When PennDOT began using LCCA, it did not possess a historical database to support the needs of the program. The first analyses used cost estimates and performance periods developed through expert opinion.
As PennDOT's LCCA process evolved, the agency set out to secure the necessary data. However, it was not necessary to develop a database specifically for LCCA, since two existing information systems were found to have the requisite information and are now used to supply data to the LCCA process. The Contract Management System contains bid history data with the ability to sort that data by project characteristics such as project size, location, and traffic. The Roadway Management System contains current and historic pavement condition inspection data. Combining the information in these two systems allows PennDOT pavement designers to develop cost and performance data inputs for use in an LCCA.
Allegheny bridges, Pittsburgh
PennDOT took a decidedly top-down approach to its LCCA implementation. The department reviewed its entire pavement design and selection process. Then the PennDOT director created a special task force to review new technologies for their applicability to Pennsylvania's transportation system. LCCA was chosen as a methodology that met PennDOT's requirements for determining long-term agency and user costs.
Working with internal experts, the Pennsylvania State University, and industry groups, PennDOT developed its Highway Geometric Design Manual and its Pavement Policy Manual. These manuals standardized all pavement design processes, including LCCA. By the mid 1980s, these manuals were being used by every PennDOT pavement designer.