High Collision Concentration Location: Table C Evaluation and Recommendations

This report describes the research work that was conducted under PATH Task Order 5215 and its extension Task Order 6215, “Methods for Identifying High-Concentration Collision Locations (HCCL).” The subject matter is related to regularly published Caltrans reports, so-called Table C, that are used to screen for and investigate locations within the California State Highway System that have collision frequencies significantly greater than the base or expected numbers when compared to other locations. The accuracy and reliability of such reports are critical as Table C is the basis for follow-up field investigation as well as potential safety improvements. In recent years, a Caltrans Table C Task Force reviewed the practices of Table C and subsequently made recommendations for improvements based on the feedback from the users of such reports. Some immediate revisions were made to correct certain issue addressed by the Task Force, yet it was clear from the review that a more thorough research effort should be made to establish solid and sound methodologies to carry out the screening and identification of HCCL so that the overall execution of safety investigation and safety improvements performed over the California State Highway Network can be more efficient and consistent. This project arises from the needs to address these problems. During the course of the project, the research team from the Traffic Safety Center and California PATH Program of University of California at Berkeley conducted extensive literature reviews and surveys, and interacted with a number of out-of-state agencies and experts to gather the latest information and techniques in dealing with the HCCL subject matters. The issues involving HCCL are broad as they cover a wide range of spatial and temporal parameters. Furthermore, the methodologies deserve to be investigated in depth as there are many mathematical and statistical details that may affect the outcome of the Table C process.