AbstractA safety performance function (SPF) is a statistical equation to predict the expected crash frequency for a certain roadway facility, mainly as a function of traffic exposure indicators. Roadway characteristics, such as pavement surface conditions and road geometry that could have critical effects on highway safety, have not been fully considered for the estimation of crash rates. In this study, four database systems managed by the Oklahoma Department of Transportation (ODOT) were utilized to integrate various safety-related roadway characteristics into the SPF development process. Roadway crashes, pavement skid resistance, pavement management system (PMS) condition data, and traffic data from 2012 to 2016 in Oklahoma were acquired for the interstate highway and selected US and state highways. An enhanced SPF was subsequently developed based on negative binomial regression models with a log-linear relationship between the crash frequency and roadway characteristics. Besides the traffic exposure indicators being currently considered in the AASHTO Highway Safety Manual (HSM), pavement friction and several roadway characteristics exhibited statistically significant influence on highway crashes. The enhanced SPF can assist in well-informed decisions for the selection of pavement preservation and maintenance practices in Oklahoma.