Assessing Injury-Severity Outcomes in Wet-Pavement Conditions: Exploring the Impact of Pavement Skid Resistance through Temporal Analysis with Random Parameters and Heterogeneity in Means and Variances

This study explores the effect of pavement skid resistance values on the injury-severity outcomes during wet-pavement condition crashes. The temporal shifts in the effects of explanatory variables on the injury-severity outcomes of wet-pavement crashes are also explored. Utilizing 1,553 single-vehicle crashes on wet-pavement conditions on Florida State highways during a period of 4 years (from 2016 to 2019 inclusive), separate yearly models of driver-injury severities (including possible outcomes of severe injury, minor injury, and no injury) were estimated by the random parameters logit with possible heterogeneity in the means and variances of random parameters. Likelihood ratio tests were conducted to examine the overall stability of model estimates across years, and the marginal effects of each explanatory variable were also considered to investigate the temporal stability of the effect of individual parameter estimates on the injury-severity probability of wet-pavement crashes. A wide range of variables potentially affecting injury severities was considered, including driver, vehicle, and temporal characteristics, as well as roadway features and environmental conditions, and a combination of driver characteristics and pavement conditions. The findings showed statistically significant temporal instability, which likely resulted from the evolution of the influence of factors that affect wet-pavement condition driving behavior over time.