Rest Period Characteristics Under Highway Truck Traffic for Mechanistic-Empirical Designs of Asphalt Concrete Pavements

Fatigue cracking due to repeated truck traffic loads is the leading cause of failure of asphalt concrete pavement in many locations. Rest periods, referring to the time intervals between successive trucks, may allow for partial or full recovery from fatigue damage and in turn extend pavement fatigue life. This study examines the characteristics of rest periods using traffic data from 40 weigh-in-motion (WIM) stations installed on California state highways and evaluates their effects on pavement performance using a mechanistic-empirical simulation program, CalME. Truck traffic data were extracted from these WIM stations at selected periods throughout 2015. Rest periods, the probability distribution of rest periods, and quantiles of cumulative rest periods were calculated. Regression and statistical analyses of the 0.5 quantiles (i.e., median) of rest periods were also performed for different spectrum groups and seasons. It was found that rest periods are strongly correlated with the truck traffic volume regardless of the WIM station location or season. The actual rest periods based on the nonuniform truck traffic measured from the WIM data were found to be slightly shorter than the corresponding theoretical average rest periods for uniform traffic (ARP-UT), currently assumed in CalME, likely due to truck-following. This theoretical value assumes an equal time interval between trucks at all times. After comparing pavement performance with and without rest periods using CalME, it was found that rest periods have significant influence (a 30% difference) on pavement cracking. CalME simulations also show that the difference in pavement performance caused by the difference between the actual rest periods and the ARP-UT is minimal. Continued use of the ARP-UT is therefore recommended to account for the effect of rest periods in pavement design.