Volume 2 of the recently published Highway Safety Manual (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 for local Oregon facilities. Therefore, the goal of this research project was to calibrate the HSM predictive method SPFs for conditions in the State of Oregon.
In the HSM predictive methods, the total expected crash frequencies for a facility are estimated by combining SPFs and crash modification factors. The SPFs are first used to calculate estimated crash frequency for a base condition. Next, the estimates are modified by applying crash modification factors (CMFs) to address non-base condition characteristics for specific segment and intersection locations. The predictive method can be used to estimate safety separately for intersections and segments. Currently, the HSM includes predictive methods for rural two-lane two-way roads; rural multilane highways, and urban and suburban arterials. All associated SPFs for these facility types should be calibrated. This project includes development of the associated segment and intersection type SPFs shown in Table 1.1. This table shows the specific SPFs included in the HSM and calibrated for Oregon conditions as a result of this research effort. In addition, there are a number of default crash distributions and parameters that can be calculated for the local conditions (these are shown later in Table 5.6)
About the Oregon Department of Transportation
“The Oregon Department of Transportation was established in 1969 to provide a safe, efficient transportation system that supports economic opportunity and livable communities for Oregonians. ODOT develops programs related to Oregon’s system of highways, roads, and bridges; railways; public transportation services; transportation safety programs; driver and vehicle licensing; and motor carrier regulation.”