Modeling the impact of roadside frictions on traffic flow under mixed traffic conditions: Case study of Wolayta Sodo City, Ethiopia

Street trading, unauthorized on-street parking, and spillover of pedestrian traffic, among other roadside frictions, are unregulated in fast-growing cities but pose operational challenges to urban road operators. The goal of the study was to model and evaluate the influence of these roadside frictions on the flow of traffic in mixed traffic conditions at Wolaita Sodo City. Field data comprising vehicle speed, flow, and density, pedestrian overflow and density, effective road width, and roadside parking were collected at three selected high, medium, and low friction site sections. Using the Green Shields macroscopic model and the multiple linear regression method, the analysis of speed and capacity was carried out. The site with the highest friction had the greatest amount of degradation, where the average speed was 15.7 km/h, while the capacity was 16% less. On the other hand, the low-friction site operated at an average speed of 38 km/h and managed to maintain normal capacity. The R 2 values for the multiple regression models were 0.971, 0.819, and 0.327 in high, medium, and low friction, respectively. Moreover, vendor density, pedestrian spill-over, and on-street parking most impacted the reduced speed and capacity. The findings suggest that immediate, low-cost, and context-appropriate interventions, including designated vending zones, regulated parking management, and improved pedestrian infrastructure, are essential to mitigate roadside frictions and improve traffic flow efficiency. The results provide evidence for governing urban traffic in mixed-traffic situations.