Effects of Berlin speed cushions in urban restricted speed zones: a case study in Bari, Italy

The widespread European policy towards urban sustainable mobility requires some engineering-related interventions on the existing urban road network, such as traffic calming measures. There is a substantial amount of research assessing the effects of different traffic calming measures, even if there is no unanimous evidence for some of them, such as speed cushions (in particular Berlin speed cushions). Some research on speed cushions has been conducted, even if different results were achieved, also varying with the country and context of installation. Moreover, some of these studies are old and they need to be updated, given the continuous transformation of urban environments. In agreement with the City of Bari, thanks to ASSET-Puglia Region funds, the Italian Ministry of Infrastructures and Transport has granted permission to install speed cushions on three urban streets located in restricted speed zones (≤30 km/h) in the City of Bari, to test their effects on vehicular traffic. In this context, this article is aimed at assessing the preliminary results obtained, considering the effects on vehicular speeds. The study design is a typical before-and-after study, in which speeds are measured using a laser speed gun on the three selected road segments before and after the implementation of speed cushions (for each segment, the cushion has a different width). Visual observations were also useful to detect the effects of speed cushions on trajectories and speeds of two-wheeled vehicles. The preliminary analysis of speed profiles revealed a consistent decrease in speed for all the three test sites (in particular the operating speed V85, which is reduced by up to approximately 30%). Moreover, it seems that the decrease in speed is more evident as the cushion width decreases.