Degradation of friction performance indicator over the time in highways using linear mixed models

Abstract

Pavement Management Systems use models describing performance indicators and can be used to plan future maintenance and rehabilitation activities taking into account the safety and economic requirements. The COST Action 354 (Long Term Performance of Road Pavements), with the participation of experts from 15 European countries, has established a list of seven performance indicators. Skid resistance and texture are interrelated in the sense that texture can be considered to be one of the explanatory variables of skid resistance and both have a major bearing on road safety. Using the database provided by a Portuguese motorway concessionary, this study aimed to develop and validate linear mixed-effects models to describe the degradation of friction performance indicator, throughout the time, based on the formula established by COST, and identify whether the traffic, climate conditions, pavement structure, and geometric characteristics of the highway influence that behavior. To accomplish these main objectives, linear-mixed models with two random effects (one in the intercept and another associated with the slope in the Time variable) were considered for a 2-level data set (level 2 distinguishes the road sections and level 1 represents the repeated measures made over time). Two approaches were made: a model that includes only the variables inherent to traffic and climate conditions and another including the factors inherent to the highway characteristics. Results confirm that the traffic, climate conditions, pavement structure, and geometric characteristics of the highway influence the degradation of friction performance indicator.