The Theoretical and Actual Trends of the Remaining Service Life

Some State Highway Agencies (SHAs) use time series cracking, International Roughness Index (IRI), and/or rut depth data to calculate the remaining service life (RSL) of pavement sections. Others convert the distress data to distress indices and use them to calculate the RSL. Still others do not calculate the RSL. The time series distress data could be modeled using various mathematical functions. For example, exponential functions for IRI, power functions for rut depth, and logistic or S shaped curve for cracking. The appropriate mathematical function could be used to calculate the RSL of a pavement section. The RSL is defined as the time in years between now and the time when the pavement conditions reach a pre-specified threshold value. Theoretically, the RSL value must decrease by one year for every elapsed physical year unless some actions have been taken to restore the pavement condition. Hence, under normal condition, the RSL of the do-nothing pavement sections must decrease by one year for every year of elapsed time. To verify the theoretical trend of RSL, time series distress data for pavement networks were requested and obtained from four SHAs. The data were analyzed and the RSL of the do-nothing pavement sections were calculated. This paper shows that for some pavement sections, the trend of the calculated RSL values matches the theoretical trend while for others they did not. For some of these cases the data were affected by some routine maintenance activities that were not properly documented by type and/or locations.