Calibrating the HSM Predictive Methods for Oregon Highways

Abstract

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.17.

Safety Evaluation of Curve Warning Speed Signs

“…The TTI team members ultimately recommended the use of the compass method for providing more reliable and repeatable signing results combined with the corridor truck speeds as indicated above. Dixon and Rohani (2008). Figure 3.1 demonstrates the site sampling procedure developed for this previous research effort.…”

A random forests approach to prioritize Highway Safety Manual (HSM) variables for data collection

“…Several of the variables are often unavailable in most of the agencies' databases. During the process of deriving calibration factors for different jurisdictions, several studies identified data collection efforts as one of the most challenging tasks [2,[4][5][6]. Collecting and maintaining all the data variables on the entire road network for the purpose of the HSM implementation are not considered cost feasible.…”

Improved Criteria for Estimating Calibration Factors for Highway Safety Manual (HSM) Applications

“…Although the number of sites varied by years, the sample size used in the study exceeded the HSM's minimum recommended criteria. Dixon et al (2012) developed calibration factors to apply the HSM predictive method in the state of Oregon. Calibration factors were determined for all the segment and intersection types discussed in the HSM, using three years (2004)(2005)(2006) of crash data.…”

“…Based on the other states' practices on the selection of minimum segment length (Srinivasan et al, 2011 andDixon et al, 2012), segments shorter than 0.04 miles were not considered in the analysis.…”