Safety Performance Functions for Mountain Two-lane Rural Roads in Ecuador

Context: The design and operation of two-lane rural roads in mountainous terrain pose unique challenges, potentially leading to specific geometric configurations with an increased risk of road accidents. While predictive models like the Highway Safety Manual (HSM) and Safety Performance Functions (SPF) are widely used around the world, their application in Ecuador's mountainous regions remains unexplored. Method: This study collected design and operational variables from 25 roads in the Ecuadorian Andes to propose SPFs specific to two-lane rural roads in mountainous environments. Crash data from 2017-2019 were utilized to develop 12 SPFs, which were further validated with information from 2020-2021. The SPFs were categorized based on three types of crashes (total, fatal + injury, property damage only) and various ranges of annual average daily traffic (AADT). Results: The outcomes of this study include the development of 12 SPFs tailored to Ecuador's mountainous regions. These SPFs estimate the average expected frequency of accidents for existing conditions, alternative scenarios, or proposed new road projects. Conclusions: The proposed SPFs fill a significant gap in road safety research in Ecuador, offering a valuable tool for assessing accident probabilities in two-lane rural roads in mountainous terrain. This research contributes to enhancing road safety for both existing roads and future projects, providing valuable insights for transportation planning and design. Further research opportunities lie in applying these SPFs to additional regions and refining the models based on evolving traffic and road conditions.