Development of Accident Modification Factors for Rural Frontage Road Segments in Texas

Frontage roads are most frequently used in rural and urban environments along freeway and full-controlled principal arterial corridors. Their primary function is to distribute and collect traffic between local streets and interchanges. They have been the primary design solution for providing access along Texas rural freeways and full-controlled principal arterials. With the growing public demand for safer streets and highways, state and national transportation agencies have developed safety programs that emphasize public education, accelerated highway renewal, community-sensitive street systems, and innovative technology to facilitate safe highway design practices. Unfortunately, there currently exist no reliable tools, including the ones proposed in the upcoming Highway Safety Manual, that specifically address the safety performance of rural frontage roads. The original research on which this paper is based is aimed at developing a safety performance function (SPF) for rural oneand two-way frontage roads in Texas and, through the modeling effort, estimate accident modification factors (AMFs) for quantifying the relationship between changes in highway geometric design characteristics and frontage road safety. To accomplish the objectives of this study, an SPF was estimated using data collected on frontage roads located along rural freeways in central Texas. The findings from this research show that wider lane and shoulder widths are associated with a reduction in segment-related collisions. In addition, the data suggest that edge marking presence has a significant impact on the safety performance of rural two-way frontage roads. However, the magnitude of the crash reduction due to marking presence was significant and believed to overstate the true benefit of such markings. The results also show that the SPF developed for this research indicates that rural frontage road segments experience about the same number of severe crashes as typical rural twolane highways for the same traffic volume. Differences in turning volume and weaving activity on these two facility types may explain the subtle differences noted in the SPF estimates for the two facility types.