Transition from Manual to Automatic Rutting Measurements: Effect on Pavement Serviceability Index Values

The Pavement Serviceability Index (PSI) is used by New Mexico Department of Transportation (NMDOT) to express the serviceability level of a pavement section at the network level. The PSI is calculated with distress ratings (including rutting) and roughness data. Currently, rut depth data collected with two NMDOT-owned 3-point profilometers are not used as an input in the calculation of PSI values. The main goal of this project was to develop and recommend a procedure to substitute automated rut depth for rutting ratings from manual surveys. For planning and reporting purposes, it is important for NMDOT to maintain the consistency of the methods and data used to calculate PSI values and to document any change implemented so that comparisons of current and past conditions and performance evaluations of the network can be made. The transition from using manual survey ratings to automated rut depth measurements should introduce the smallest possible difference in the calculated PSI values and the overall condition rating of the highway network. Three procedures or approaches are presented and discussed. Regression analyses were applied to the rut depth and PSI data. Recommended Approach A proposed preserving the current PSI formulation and factors and converting the automated rut depth data into equivalent rutting ratings. Alternative Approach B proposed minor modifications to the PSI formulation. A third approach (Approach C) was considered and evaluated, but was not recommended. Results of the statistical tests performed on the data and results are also presented. The ratings from manual surveys and automated rut depth data were compared with detailed measurements of transverse profiles to evaluate the data from these two methods. This report includes an implementation plan for the recommended and alternative approaches.