Speed Profile Characterization of Medium-Sized Vehicles and iRAP Star Rating Assessment on Mountainous Rural Roads: Loja-Ecuador Corridor Case Study

Abstract

Road safety in mountainous rural highways such as Loja-Catamayo (Ecuador) presents significant engineering challenges due to geometric deficiencies and pavement surface conditions that increase risks for medium-sized vehicle operators. This study analyzed the influence of road geometry (grade and horizontal curve radius), International Roughness Index (IRI), and iRAP star rating classification on operating speed through 50 speed profiles recorded with Speed Tracker (iPhone 15 Pro), pavement roughness measurements via Roughometer III, and iRAP coding in ViDA. Analysis of Variance (ANOVA) in Minitab revealed a mean operating speed of 56.48 km/h, with statistically significant effects from grade (p<0.001, F=19.07), curve radius (p<0.001, F=27.53), and IRI (p<0.001, F=14.66), but not from iRAP classification (p=0.711). Minimum speeds were recorded on tight curves (43.85 km/h), uphill grades (47.17 km/h), and poor pavement surface conditions (41.40 km/h). The results highlight a statistically significant relationship between mean operating speed of medium-sized vehicles and both horizontal curve radius and grade, as well as pavement surface condition; however, no statistically significant relationship was found with the results of the road safety assessment in the study corridor