Influential factors on speed reduction at vertical deflection devices in mixed traffic environments

• In mixed traffic, several factors affected speed reduction at vertical deflection devices like speed humps and speed tables. • Key factors included speed before device, vehicle type, device height, roadway grade, intersection proximity, and roadway width. • 85th percentile crossing speeds for passenger cars and motorcycles were 37.8 and 39.1 km/h, respectively, with 28.3 and 25.8% reductions. • Vertical deflection devices had a greater impact on reducing the speed of passenger cars than motorcycles. Vertical deflection devices are widely implemented as traffic calming measures, designed to compel drivers to reduce their speeds to ensure a comfortable passage over them. However, these measures are primarily adapted from practices in developed countries, raising questions about their effectiveness in mixed-traffic environments. This study aims to investigate the factors influencing speed reductions in such contexts. The research focused on driver behavior while traversing three-speed humps and seven-speed tables located within a campus area. An Unmanned Aerial Vehicle (UAV) was employed to capture vehicle speed profiles as they navigated these devices. 2,101 speed samples were recorded, comprising 1,152 passenger cars and 949 motorcycles. Video recordings enabled the analysis of spot speeds at 10-meter intervals, starting 50 m before and extending 50 m beyond each device. Multiple linear regression analysis was utilized to identify the factors affecting speed reductions. The findings revealed that vertical deflection devices exerted a more substantial impact on reducing the speeds of passenger cars compared to motorcycles. Key factors significantly influencing speed reduction, ranked from most to least influential, included before-speed, vehicle type, device height, roadway grade, proximity to intersections, and roadway width. These findings offer valuable insights for refining existing guidelines on the design and placement of vertical deflection devices in mixed-traffic environments.