Effects “Bologna Città 30” Speed Limits: Data-Driven Analysis with TomTom

Cities around the world face a phenomenon in which they are progressively working to expand the proportion of their street network with speed limit policies, aiming to enhance road safety. Extensive research supports the effectiveness of 30 km/h speed limits in achieving these safety goals. However, this policy can also have both positive and negative implications on other factors such as emissions, noise levels, driver behaviour, and overall mobility patterns. The research aims to analyse the effect of the policy "Bologna Città 30", which imposes a speed limit of 30 km/h in Bologna, Italy. This policy is assessed by comparing the two scenarios, before and after implementation, identifying key variables that influence the change of speed, and analysing public perceptions of such change. The methodology begins with a literature review, identifying main factors and indicators, to better understand the policy framework. Then, data collection is made, followed by data processing, and data analysis design. Data are analysed using spatial analysis, statistical analysis, through ANOVA and the Tukey HSD test, and the public perspective. Two data based are used: a) TomTom traffic data, to assess speed variations and the influence of different road functional classes (FRC) on compliance with the policy; b) data from the municipality of Bologna, which provides vehicle counting and questionnaire results. The results show that the road functional classes and whether a road is subject to policy significantly influence average speed. The comparisons before and after the implementation of such a policy reveal that the number of vehicles and the average speed on the roads have decreased, and the difference in the speed variations between the different FRCs can be perceived more clearly after the implementation of the policy. In addition, the roads where the policy is not applied show a slight decrease in the average speed. Another key finding is that citizens' perception correlates with actual levels of speed; the roads perceived as the most dangerous are indeed those with the highest speed, emphasising the impact that the policy could have on public attitudes. This study provides valuable information for policymakers by highlighting how different types of roads meet regulations regarding speed limits. These roads can be closely monitored for speed violations, and additional studies to measure their impact on accident rates would be worthy to be done. The results show how speeds rarely exceeded 30 km/h in densely inhabited urban contexts (even before the policy), but show that interventions tailored to specific FRCs could optimise the implementation of this policy and improve public acceptance. Finally, this research could be useful for other cities to have an insight into the possible effects of introducing speed limits and on possible implementation of such a policy.