Safety effectiveness of inclusive motorcycle lane: A case study in Hat Yai City, Thailand

• Inclusive motorcycle lanes (IML) effectively separate motorcycles in mixed traffic and reduce their speeds. • IML use increases with higher traffic volume and motorcycle share. • Lateral clearance between motorcycles and cars improves, enhancing overall traffic safety. • Smaller speed differences between motorcycles and cars support smoother and safer flow. • Odds ratio analysis shows reduced crash likelihood from excessive motorcycle speed after IML implementation. In Thailand, motorcyclists are the most vulnerable road users, with the highest number of road traffic deaths compared to other road users. This study examines the effectiveness of installing inclusive motorcycle lanes (IMLs) through a pilot project in Hat Yai, serving as a case study. The study utilized an unmanned aerial vehicle to capture video footage of traffic movement on the study bridge during off-peak periods before and after installation at 3, 6, 9, and 12 months, respectively. The YOLOv8 model was also applied to detect and track two classes of study vehicles (i.e., motorcycle and car) from the recorded video. The study then examined vehicle trajectory, proportion of IML usage, speed changes, and lateral clearance between motorcycles and cars before and after the installation. The findings indicate that approximately 71.45 % of motorcyclists used the IMLs in both directions, a notable increase from 6.17 % on prior shoulder lanes. The 85th percentile speeds decreased significantly by 3.1–15.4 km/h (5.1–23.6 %), while the lateral clearances increased by 0.624–0.656 m (26.89–28.30 %). Risk analysis using the odds ratio method yielded a value of 0.83, indicating a 17 % reduction in the likelihood of motorcycle crashes associated with excessive speed. These findings suggest that IMLs contribute to improved motorcyclist safety by encouraging safer speeds, increasing lateral space, and reducing the severity of crashes. The demonstrated safety benefits support the immediate application of IMLs in similar roadway environments.