Evaluation of Long-Term Pavement Performance Profile Data for Flexible Pavements

Abstract

The Long-Term Pavement Performance (LTPP) program has collected longitudinal profile data for a wide variety of pavements nationally for almost 20 years. The program is managed by FHWA, which also maintains the LTPP database. The Office of Highway Policy Information, also of FHWA, increased the frequency with which state agencies must perform longitudinal profile testing for the Highway Performance Monitoring System (HPMS) from biannually to annually. This paper looks at the LTPP program data to see if the increased frequency being required for HPMS is justified. All data sets used in the study were from general pavement studies (GPS) with either aggregate base or asphalt-stabilized base. The international roughness index (IRI) and the time between successful data collections were used to plot IRI versus time for each section. A polynomial equation of the form ax2 + bx + c was fit for each site, and the polynomial was used to calculate the number of years to a 30-point change in IRI by the use of English units of inches per mile. Plots of the change in IRI versus the time between test events by climatic region were also made. As has been reported by others, the largest contribution to the future IRI is the initial IRI. In all climatic zones, the time required to reach a 30-point increase in the IRI decreased with increasing initial roughness. Straight lines fit through the change in IRI versus time between tests had very low slopes that ranged from 0.0052 to 0.0096 point per day. Even at the maximum slope, it takes 3 years to reach a 10-point change in the IRI, using English units. On the basis of the LTPP program data for GPS flexible pavements nationally, annual testing is not warranted.