Analysis of LTPP Profile Data for Jointed Concrete Pavement Sections

Abstract

Incremental changes to a pavement-surface profile have long been considered a primary measure of pavement performance. As a result, the Long-Term Pavement Performance (LTPP) program of the Strategic Highway Research Program has allocated considerable resources for collecting accurate profile data on all general pavement studies (GPS) sites annually. As of June 1995, the profiles of the rigid pavement sites had been measured an average of four times, with many sites having been measured seven times. The data are collected and processed in the field, generating several statistical measures of pavement profile for each wheelpath, including the international roughness index (IRI), present serviceability index (PSI), slope variance, and root-mean-square vertical acceleration (RMSVA) at selected wavelengths. The focus of this analysis is on the primary profile statistic, the IRI. The profile data were downloaded from the National Inventory Management System (NIMS) and extensively analyzed using selected statistical techniques. The objective of this effort was to conduct a thorough analysis of the response variable, the IRI. The analysis included univariate, bivariate, and multivariate analytical techniques to determine which prediction variables are useful for predicting the IRI. Although many of the primary independent variables had significant correlations with the IRI, others did not. Various measures of traffic had particularly poor correlations with the IRI. Several regression models are also presented along with advantages and limitations of the prediction and response variables. The results of a detailed analysis of the within-year and year-to-year variability in IRI measurements are also included. The coefficient of variation in year-to-year measurements averaged 4.2 percent for the jointed plain concrete pavement (JPCP) sections (GPS-3) and 3.8 percent for the jointed reinforced concrete pavement (JRCP) sections (GPS-4). This degree of variability in year-to-year profile measurements tended to overshadow any absolute increase in IRI that may have been occurring in these sections. An analysis was then performed on every section to determine exactly which sections had statistically significant increases in IRI over time. Approximately 44 percent of the jointed concrete pavement sections exhibited statistically significant increases in IRI over time.