Calibrating The Highway Safety Manual Predictive Methods For Oregon Highways
The Highway Safety Manual (HSM) was published by the American Association of State Highway and Transportation Officials (AASHTO) in the spring of 2010. Volume 2 (Part C) of the HSM includes safety predictive methods which can be used to quantitatively estimate the safety of a transportation facility. The resulting information can then be used to provide guidelines to identify opportunities to improve transportation safety. The safety performance functions (SPFs) included with this content, however, were developed for several states other than Oregon. Because there are differences in crash reporting procedures, driver population, animal populations, and weather conditions (to name a few), the State of Oregon needs to use calibrated SPFs when applying the HSM procedures to local Oregon facilities. Currently, the predictive methods have been developed for three facility types: rural two-lane two-way roads, rural multilane roads, and urban and suburban arterial roads. In this project, the research team calibrated SPFs for all three facility types based on their historic safety performance in Oregon. The report illustrates methods of site selection, the collection of crash and site-specific data, and analysis methods for calibration. Also, the report includes an evaluation of the crash severity distribution methods. With this information, Oregon agencies can use the calibrated HSM predictive methods to assess expected facility safety performance for Oregon conditions and facility alternatives.