Improving crash predictability of the Highway Safety Manual through optimizing local calibration process

Publication date: March 2020Source: Accident Analysis & Prevention, Volume 136Author(s): Seyedehsan Dadvar, Young-Jae Lee, Hyeon-Shic ShinAbstractThe predictive method of the Highway Safety Manual (HSM) estimates crash frequency by applying an uncalibrated safety performance function (SPF) and a set of uncalibrated crash modification factors (CMFs) to each location individually; then the predicted crashes must be adjusted by a local calibration factor (LCF) at the aggregate level for at least 30–50 sites per SPF. Although this calibration procedure assures total predicted crashes will be localized, still the prediction of crashes for individual locations suffers from the aggregate localization process. An alternative approach of locally calibrating the HSM predictive method is proposed to improve prediction quality at individual locations while maintaining equality of total observed and total predicted crashes.The methodology incorporates multiple calibration factors for different components of the predictive method (SPF parameters and CMFs) rather than a single calibration factor as recommended by the HSM that only calibrates at the aggregate level. In the proposed method, the application of calibration factors expressed in both weight and power function better reflects the local conditions while still ensuring calibration at the aggregate level. The parameters are estimated through an optimization process of five different methods.Rural two-lane, two-way roads (R2U) data ...
Source: Accident Analysis and Prevention - Category: Accident Prevention Source Type: research