Pioneering Use of Continuous Pavement Friction Measurements to Develop Safety Performance Functions, Improve Crash Count Prediction, and Evaluate Treatments for Virginia Roads

Abstract

A comprehensive pavement management system includes a pavement friction management (PFM) program to ensure that pavement surfaces are designed, constructed, and maintained to minimize friction-related crashes in a cost-effective manner. FHWA Technical Advisory 5040.38 on PFM canceled a previous advisory that focused only on the reduction of wet skid crashes. This new advisory recommends continuous friction measuring equipment as an appropriate method for evaluating pavements. The study described in this report developed a pavement friction inventory by using the GripTester. The friction data were then coupled with crash records to develop a strategy for network analysis to improve the ability to predict crash rates. The crash rate analysis applied a well-established methodology for the identification of areas of high crash risk by using safety performance functions (SPF), which included empirical Bayes rate estimation from observed crashes. The current Virginia Department of Transportation SPF models can be modified to include skid resistance and radius of curvature (Interstate and primary system only) to improve their predictive power. The same methodology was also used to contrast the effect of two friction repair treatments—an asphalt overlay and high-friction surface (HFS) treatments—to explore how their strategic use could affect network-level crash rates. The result suggests significant crash reductions with comprehensive economic savings ($100 million) when applied to a single relatively rural district. These findings easily justify an aggressive state-level PFM program and support continued research to quantify the influence of other pavement-related characteristics such as macrotexture, grade, and cross slope.