Crash modification factors and functions (CMFs) are developed from historic crash data and help safety professionals estimate the expected safety impacts of specific roadway treatments. There has been a significant amount of research to develop CMFs for common safety strategies and the AASHTO Highway Safety Manual (HSM) and FHWA CMF Clearinghouse website contain many CMFs. However, there are many instances in which developing reliable CMFs with conventional crash-based evaluations is less than desirable or simply not possible. For example, using crash data to evaluate innovative intersection designs or new traffic control strategies requires years of waiting to accumulate a sufficient number of installations and crash history. Additionally, countermeasures that improve safety for rare crash types, such as pedestrian crashes, are often lacking in quality CMFs because crash data is limited. Research is needed to develop and apply new methods to developing such CMFs, specifically through the application of surrogate measures of safety such as conflicts, speed changes, and lane deviations. This approach has shown significant promise in recent research.
The objective of this research is to develop procedures for using surrogate measures of safety for estimating CMFs. The procedures will be evaluated by applying them to develop CMFs for specific safety treatments, which will be identified based on a gap analysis conducted as part of this project. To better understand the issue, the research should include an initial review of related research and a gap analysis to identify safety treatments for which needed CMFs may be developed using surrogate measures. Types of surrogate measures that could potentially be used for each treatment should be identified early on, as well. Once candidate procedures have been identified, the procedures will be fully developed and then evaluated by applying them to selected safety treatments to develop CMFs. It is expected that several new CMFs will be developed in the process, spanning a range of site, severity, and crash types and using one or more surrogate measures of safety.
One of the expected products of this project is set of crash modification factors or functions for specific safety treatments that can be incorporated in a future edition of the HSM. Another expected product of this project is a guideline document that describes new procedures for estimation and validation of crash modification factors to support informed decision making during project planning, project development, and other road safety management activities.