Speed Profile Models Under Real Urban Conditions: A Case Study of a 30 km/h Zone with Mid-Block Narrowings

When planning 30 km/h zones within a selected urban street network in a city centre, the effectiveness of applicable traffic-calming measures (TCMs) is analysed to support sustainable urban mobility and the design of safer urban streets. One of the possible TCMs is the mid-block narrowing (MBN), which has been reported in previous studies as having limited effectiveness. However, those studies were constrained by several limitations, including the lack of speed v85 analyses at different distances from the MBN and the absence of assessments of other contextual variables affecting speed. To address these gaps, speed measurements were conducted within an urban street network in the city centre of Szczecin, Poland, where several MBNs had been implemented. Speeds were recorded using SR4 sensors at nine measurement points along 12 study areas during three weekdays under dry weather conditions. The collected data were analysed and speed profiles were developed for each study area. Free-flow speed was the dependent variable, while independent variables included junction spacing, different types of entrance and exit junctions, and other contextual factors. The main objective was not only to estimate the operating speed and zone of influence of MBNs but also to identify other factors determining speed profiles between junctions. The analyses showed that speeds depend on junction spacing, street type, the type of entrance and exit junctions together with their traffic arrangement, and the streetscape elements located at the MBN. The outcome of the study was the development of a comparative framework for assessing the speed-related effectiveness of MBNs under specific contextual conditions, providing a basis for the sustainable redevelopment of selected city-centre street networks. This framework may support the implementation of 30 km/h zones in city-centre street networks when planning new interventions, comparing designs, or aiding decision-making.