Incorporating Variability into Pavement Performance, Life-Cycle Cost Analysis, and Performance-Based Specification Pay Factors (05-1912)**
Leanne Claire Whiteley, University of Waterloo, Canada
Susan Louise Tighe, University of Waterloo, Canada

This paper describes a recent research study that examined how changes in design life impacts the pavement life cycle cost (LCC) and ultimately how the reduction or addition in LCC attributed to inferior or superior in-service performance could be used as a basis for establishing a pay factor for a performance based specification. Models have been developed using data from the Canadian Long Term Pavement Performance (C-LTPP) that indicate that overlay thickness, total prior cracking, annual freeze index, annual days with precipitation, and accumulated ESALs after eight years, affect the slope of pavement deterioration for asphalt overlay pavements. One of these models, as well as data from the United States Long Term Pavement Performance (LTPP) test sites, is used to determine the service life of asphalt overlay pavements. This paper examines how the variability associated with overlay thickness, total prior cracking, and accumulated ESALs after eight years affects the service life. Furthermore, this paper considers the variability associated with the discount rate and incorporates all associated variability into the life cycle cost analysis (LCCA). The life cycle cost distributions are calculated using Monte Carlo techniques. Based on a recent study, distributions for service life and life cycle costs are developed using both the normal and lognormal distributions for overlay thickness. Using the LCCA values for typical design lives, a sensitivity analysis is subsequently performed to evaluate the impact of 10%, 20% and 30% differences in the in-service performance as compared to the design life. These LCCA differences are then used as a basis for establishing pay factors. Overall the paper attempts to relate design to in-service performance LCC and ultimate use of pay factors. Key words: pavement performance, life cycle cost analysis, asphalt overlay, pay factors.