Development of Arizona-Specific Cross-Sectional Crash Modification Factors (CMFs)

Arizona Department of Transportation's (ADOT’s) approach to selecting the location and type of safety projects in its strategic traffic safety plan relies, in part, on crash modification factors (CMFs), which are multiplicative factors used to predict how safety countermeasures will affect crash frequency and severity at a given site or group of sites based on their past performance. ADOT currently uses CMFs published in the Federal Highway Administration's (FHWA’s) Crash Modification Factors Clearinghouse. These are often developed using national data or data from other states and therefore may not be calibrated specifically to Arizona data or roadway conditions. Developing a broad array of Arizona-specific CMFs could help ADOT evaluate the safety benefits and costs of proposed and implemented projects more accurately. Another limitation of the CMF Clearinghouse database is that it does not cover all potential crash countermeasures available to state DOTs. The resulting lack of relevant CMFs can make it more difficult to secure federal funding. Therefore, there is a need to develop Arizona-specific CMFs for targeted safety projects that currently are unavailable in the Clearinghouse or other databases. Accurate and reliable CMFs could help ADOT avoid over- or underestimating the effectiveness of safety treatments. As a result, it is crucial for the agency to employ a robust CMF estimation method that can cope with the issues of traffic exposure, stochastic fluctuations of traffic crashes, and other sources of bias when evaluating the effectiveness of a specific treatment or a proposed design element. The objectives are to: (1) Work with ADOT to compile a prioritized list of six to eight implemented safety projects for which new, Arizona-specific CMFs are desired. (2) Develop a set of metrics that determine the applicability and sufficiency of CMFs for Arizona safety projects. (3) Identify implemented projects that lack applicable CMFs. (4) Develop separate CMFs by injury severity and crash type for three to six ADOT-implemented projects. (5) Document the data and processes used to develop each CMF sufficiently to allow ADOT to submit them for publication in the FHWA CMF Clearinghouse.