Measuring the readiness to become a “30 km/h city”

This paper proposes a macroscopic analysis to evaluate the “readiness” of cities to limit the street speed to 30 km/h. Floating Car Data (FCD) from anonymous GPS-based measurements are analysed for the urban areas of the major Italian cities to investigate the actual vehicle speed distributions. Ad-hoc indicators based on the average speed in the road network, the percentage of the network length with an average travel speed lower than 30 km/h, the average travel time comparing peak and off-peak hours are computed and compared for the selected cities. Analysing the percentage increase in travel times compared to free-flow speeds reveals a clear distinction between cities with uniform travel patterns and those with highly variable travel times. Results show how, for some cities, the average vehicle speed is below 30 km/h in the majority of road segments even during off-peak hours, so reductions of speed limits for road traffic would not significantly penalise the actual travel times, while for other cities a significant discrepancy in the detected speed exists between peak and off-peak hours, suggesting that low speed values are due to traffic congestion rather than street design and widespread traffic calming measures may be needed to reduce drivers’ speed. This exploratory study could represent a supporting tool for decision-makers and traffic planners to identify, prioritize and monitor the effectiveness of traffic calming measures and speed limits.