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.