The National Technical University of Athens (NTUA) has recently published a paper titled “Review of City-Wide 30km/h Speed Limit Benefits in Europe” authored by George Yannis and Eva Michelaraki. It is the first-ever scientific review of city-wide 30 km/h speed limit benefits in Europe. Evaluation results from 40 different cities across Europe (including Paris, London, Brussels, and Helsinki) demonstrated that 30 km/h speed limits have led to significant reductions: 37% of road crash fatalities, 18% in emissions, 2.5dB in noise pollution and 7% in fuel consumption (on average). Such a high societal impact for such a small change in our habits.

The aim of this work was to assess the benefits of city-wide 30km/h speed limits. On that purpose, a thorough literature review of assessment results from 40 different cities across Europe was conducted and the effectiveness from 30 km/h speed limits in terms of safety, emissions, energy, traffic, liveability and health was discussed.

The introduction of city-wide 30 km/h speed limits has resulted in saving on average 37% of lives, alongside significant positive impacts on the environment, energy consumption and public health through reduced emissions and increased walking and cycling. Results from the extensive literature review revealed that after the introduction of city-wide 30 km/h speed limit, there was an average of 23% decrease in road crashes. This reduction in crashes can be translated to a safer urban environment, as evidenced by the corresponding decrease in fatalities and serious injuries by 37% and 38%, respectively.

Streets that promote safe walking and cycling can reduce car dependency and harmful vehicle emissions that contribute to climate change. Thus, the implementation of lower speed limits resulted in significant environmental benefits, including an average 18% reduction in emissions and an average 2.5 dB reduction in noise pollution.

Furthermore, after the introduction of a city-wide 30 km/h speed limit, it was found that fuel consumption decreased by an average of 11%, indicating that lower speeds led to improved fuel efficiency and reduced environmental impact. The results align with expectations based on the general principles of traffic flow and vehicle efficiency at lower speeds.

Reducing speed limits can prompt road users to choose alternative routes or modes of transportation, which, therefore, has a significant impact on traffic volumes. Results indicated that the reduction of city-wide speed limit contributed to an average 4% decrease of traffic congestion. It was also demonstrated that 30km/h speed limits improved traffic flow and travel times as there were less stop/start traffic movements.

Reducing speed limits not only enhances road safety for all users but also facilitates better use of public space, promoting soft and active mobility while providing opportunities to reimagine urban areas. With the introduction of 30 km/h speed limits in several European cities, findings revealed that there were less stressed citizens, with fewer health problems, and, therefore, a quieter city was promoted.

From several cities examined, interesting findings per city have been revealed. For instance, a 46% and 40% reduction in road crashes was observed in London and Paris, respectively. Additionally, a 29% and 25% decrease in CO₂, NO_x and PM emissions was found in Berlin and Graz, while noise pollution dropped by 3 db in Paris. With regards to energy, a 12% and 10% reduction in fuel consumption was demonstrated in Münster and Brussels, respectively. Lastly, traffic congestion decreased by 9% and 2% in Grenoble and Bilbao, respectively.

In order to successfully implement 30 km/h speed limits in cities, it is essential to launch public awareness campaigns that emphasize on scientific evidence for the safety benefits associated with the reduced speed limit and to elucidate the rationale behind its implementation, with the overarching goal of gaining public support. An example being the NTUA Professor George Yannis high visibility campaign on running 30 Marathons in 30 months to promote city-wide 30km/h speed limits.