Developing Region-Specific Safety Performance Functions for Intercity Roads in Saudi Arabia

This study develops comprehensive Safety Performance Functions (SPFs) for various intercity road types in Saudi Arabia, including freeways, multilane highways, and two-lane two-way roads. Data spanning 2017–2019 were analyzed for five regions—Riyadh, Makkah, Eastern, Aseer, and Tabuk—using Negative Binomial (NB) regression models aligned with the Highway Safety Manual (HSM). A total of 26 SPFs were developed to predict total and fatal and injury (FI) crashes, incorporating contextual variables (e.g., tunnel density, U-turn frequency, high-speed vehicle proportion) and developing models separately for each region. It was found that as the median width increases on freeway roads in the Riyadh region, the predicted number of total and fatal and injury crashes decreases. Also, as the percentage of heavy vehicles and U-turn density increases, the number of total and fatal crashes increases on multilane roads in the Makkah region. Moreover, as the degree of curvature increases, the predicted number of total and fatal andinjury crashes increase on multilane and two-lane two-way roads in Tabuk. Lastly, in Aseer, median double marking and tunnel density along curves were significantly affecting crashes on two-lane two-way roads. This study is useful to enhance the methodology used to identify hotspots on the intercity roads in KSA.