Safety Performance Functions for Frontage Roads

Frontage roads play a vital role in the U.S.'s highway system because they serve as critical access routes between principal arterials, freeways, and surrounding businesses. Despite their importance, there have been only limited studies conducting an in-depth analysis of frontage road safety. The limited availability of suitable data for frontage roads has been a significant barrier to conducting comprehensive safety studies on these critical road segments. This study developed a robust methodology that allows for the correct attribution of crashes to the corresponding frontage road segments. This methodology is a novel contribution to the field of transportation safety research, as it addresses a critical data challenge that has hindered the advancement of frontage road safety analysis in the past. Moreover, there is limited research into developing the safety performance functions (SPFs) and crash modification factors (CMFs) for frontage roads. In fact, the first edition of the Highway Safety Manual does not include the SPFs for frontage roads. In this study, the authors considered 4 years (2017-2020) of crash data for conducting a comprehensive analysis of four types of frontage road (rural one-way, rural two-way, urban one-way, and urban two-way) and developed the SPFs and CMFs specifically tailored for frontage roadways in Texas, U.S. Several CMFs were developed in conjunction with the SPFs. This study developed CMFs for left and right shoulder widths, access point density, presence of entrance and exit ramps, posted speed limit, and the horizontal curve density.