The Impact of Speed Bumps on Traffic Flow Speed in Urban Road Networks

Traffic safety is a fundamental element of urban mobility, and speed bumps remain one of the most widely used measures for reducing vehicle speeds on local streets. This study investigates how different types of speed bumps influence traffic flow speed in the City of Zagreb, Croatia. A total of 208 locations were surveyed across all city districts, where geometric characteristics, regulatory compliance, and local contextual features were recorded. In addition, UAV monitoring was conducted at eight representative sites, capturing 906 vehicle trajectories and enabling the extraction of speed profiles at two measurement points per location, together with vehicle classification. This combined approach—integrating UAV-based speed tracking with a detailed geometric compliance assessment—provides a novel and reproducible methodological framework for evaluating vertical traffic-calming measures under real operating conditions. The results show substantial differences in performance between bump types. Raised platforms reduced vehicle speeds by up to 53%, while narrow platforms achieved reductions of up to 49%. In contrast, modular rubber elements exhibited noticeably weaker performance, particularly for heavy vehicles. These findings differ from previous research that has primarily focused on single bump types or limited samples and reported mixed effectiveness depending on height and material. The reductions observed in this study are operationally relevant, as they indicate which bump designs reliably maintain speeds below the 40 km/h safety threshold required on residential streets and around schools. By linking bump geometry and compliance with actual driver behaviour, this study offers a practical and transferable framework that can support urban traffic-safety planning, standardization of vertical calming devices, and improved selection of appropriate measures for mixed-traffic urban environments.