Sensitivity of Flexible Pavement Thickness to Traffic Factors in Mechanistic-Empirical Pavement Design

In an effort to minimize the risk of overdesign or underdesign of pavement structures in the Mechanistic-Empirical Pavement Design Guide (MEPDG) in Alabama, sensitivity analysis was utilized to examine the potential for implementation of various levels of traffic inputs. Changes in required pavement thickness as a result of differences between nationwide, statewide, regional, and site-specific traffic factors were used as sensitivity indicators. The effects of traffic inputs on pavement design were deemed to be practically significant when the thickness needed to maintain an acceptable level of pavement performance changed 1.3 cm (0.5 in.) or more from the baseline thickness developed from statewide traffic inputs. This paper presents the sensitivity analysis results for nationwide traffic inputs and direction-specific inputs when the effects of each were compared with the effect of statewide inputs on pavement thickness. Recommendations include the use of a procedure that incorporates required pavement thickness when determining an appropriate level of traffic inputs. Based on the results of the sensitivity analysis, statewide inputs are preferred over the default nationwide values; however, when the impacts of direction-specific inputs on pavement thickness exceed sensitivity criteria, statewide traffic inputs are not sufficient and direction-specific inputs or cluster-averaged inputs are recommended.