Edgar de León Izeppi

The safety of a pavement surface can be characterized by properties such as skid resistance and texture. All pavement surfaces should be constructed and maintained such that they meet the friction demand of the roadway. Decades of research suggest that skid resistance is most critical on wet pavements; therefore, most highway safety management decisions are often made based only on wet pavement crashes. However, recent studies have found that skid resistance may also impact crash risk on pavements that are dry. Since pavements are dry more often than wet, management decisions based only on wet crashes are formulated from smaller data sets. If skid resistance also has impact on crash risk on dry pavements, then considering dry crashes in highway safety management can increase the number of crash observations, which could improve safety analysis, leading to better maintenance decisions. This study used visual and regression analyses to investigate the relationship between skid resistance and crash occurrence for both dry and wet conditions. Figures were developed to visually illustrate the crash–friction relationship. Statistical regression was used to generate crash models, and the estimated regression coefficients were used to evaluate whether there was a statistical relationship. The findings show that skid resistance influences crashes in both dry and wet conditions, but there is greater impact in wet weather.

Previous comparisons of pavement friction equipment focused on the harmonization of devices that measure pavement friction, but did not assess the agreement of the measurements between them. Harmonization was accomplished with normalization of the measurements through adjustment to a standard slip speed and use of macrotexture measurements in models of the friction–speed relationship. A problem with this procedure was that the true value of friction on which the comparisons were made was assumed. When true values remain unknown, valid comparisons between two devices require the use of agreement assessments. Limits of agreement (LOA) were used to compare two pavement friction devices. The first comparison was made with one run to illustrate LOA. A second comparison with two runs was made to gain understanding of their repeatability and use in LOA. A more complex LOA procedure was conducted with multiple runs of the two devices. The results of another study that used LOA between another pair of pavement friction devices showed a better agreement. The obtained LOA results showed a 95% confidence level, which was considered not adequate. A comparison between the 95% repeatability coefficients and the 95% LOA computed for the two devices indicated that factors other than repeatability were responsible for the lack of agreement. Use of the LOA method of analysis should be considered before harmonization of different devices. Predictive models based on correlation are not recommended for comparing pavement friction measuring devices.