Transferability and Calibration of Highway Safety Manual Performance Functions and Development of New Models for Urban Four-Lane Divided Roads in Riyadh,Saudi Arabia

Abstract

The first edition of the Highway Safety Manual (HSM) provides a number of safety performance functions (SPFs) that can be used to predict severe collisions on a roadway network. This paper examines the calibration of the HSM SPFs for urban four-lane divided roadway segments with angle parking in Riyadh, Saudi Arabia, and the development of new SPFs. This study first calibrated the HSM SPFs by using HSM default crash modification factors (CMFs) and then proposed new local CMFs, which adjust the estimation of calibration factors by using fatal and injury crash data. In addition, new forms for specific SPFs were further evaluated to identify the best model by using the Poisson–gamma regression technique. It was found that the jurisdiction-specific SPFs provided the best fit of the data used in this study and would be the best SPFs for predicting severe collisions in the city of Riyadh. The best fatal and injury model describes the mean crash frequency as a function of the natural logarithm of the annual average daily traffic, segment length, speed limit, and driveway density. The study found that the HSM calibration using Riyadh local CMFs outperformed the calibration method using HSM default values. Based on these results, potential countermeasures were proposed to reduce the number of severe crashes on Riyadh urban roads, and the potential for HSM application in Saudi Arabia is addressed.