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Città 30 through data

How has the city of Bologna changed with the new limits?

Bologna is changing

In January 2024 the initiative Città 30 was enacted. Most of the city streets became traversable with a maximum speed of 30 km/h, while only the main arterial roads kept the 50 km/h limit. The scope behind it is to diminish traffic and traffic-related accidents, while promoting alternative forms of mobility and positively impacting pollution. Bologna is the first city in Italy to introduce this ruling and, despite being a well-tested project in various cities around Europe (like Vienna, Paris, Lyon, Montpellier and Madrid among others), it still sparked contrast among citizens.

How can we measure it?

Today, after more than a year since the provision was introduced, we aim at addressing through a data-driven analysis the real impact Città 30 had on Bologna, measuring car traffic, air pollution, bike usage both on a temporal and spatial axis, by taking into account data about different areas and years. All data used in this project have been taken from OpenBologna.

QUESTION ONE
How was Car Use affected by Città 30?

In this section, we analyze car-related traffic on a spatial and temporal account. Heatmaps show areas with intense traffic, allowing to see which streets are most affected by it and compare them.

By clicking on the buttons, it will be possible to swap the visualization of data from different years.

By clicking on a street, it will be possible to visualize a chart highlighting trends between years and compare them to the average in the whole metropolitan city.

5% decrease

Available data only shows a decrease of 3.2% in 2024 and 5% up to June 2025 (in contrast to the 8% reported by the official website).

QUESTION TWO
DO PEOPLE CHOOSE TO USE BIKES MORE?

No sign of Correlation

Bike usage has been rising after the introduction of Città 30, as the graph shows. However, it seems the event was only partially caused by the new limits, as the positive trend traces back to 2021, and in 2022 bike traffic reached pre-covid levels.

It seems that despite there being a higher percentage of people choosing bikes as an alternative mobility method, the correlation with Città 30 seems to be insignificant.

QUESTION THREE
Has the center been more impacted?

30-zones vs non-30-zones

Since now, we analyzed measures on a temporal account, but another significant information to register is the difference in trends between 30-only zones and 50-or-above ones during 2024.

In the city center, both bike and car average traffic is significantly lower (34% less for cars and 43% less for bikes), revealing that the inner part of the city has been impacted positively in respect to streets that have limit equal to or greater than 50.

34% less cars

43% less bikes

QUESTION FOUR
How has Air Quality changed in the 30-zone?

Impact on Air Pollution

We evaluated the effects of the new policy on air quality using data from two monitoring stations near Bologna’s center: Porta San Felice and Giardini Margherita. These stations measure several gases and their emissions over time, each compared to EU and WHO threshold. Only O3 and NO2 emissions registered a significant decrease with the introduction of the new law, the latter reflecting results from other European cities which introduced similar provisions.

PM10 are tiny airborne particles from sources like dust and traffic that can be inhaled, irritating the lungs and worsening respiratory and heart conditions. The introduction of Città 30 had little impact on their presence.

Irrelevant Electric Vehicles presence

We also wanted to explore if there was some correlation between the change of air quality and the growth of electric car vehicles. While it is true that their growth in usage among the population shows a positive trend (+1% from 2019), the percentage over the the total count of cars is too little to have any significant impact on data.

CONCLUSION
What is happening in Bologna?

Similar provisions have been enacted and experimented in other cities in Europe, as mentioned at the beginning of our study. However, results that show an alignment with trends encountered in them might require some time in Bologna. We want to review here some points emerged in our study:

Q1 — How was Car Use affected by Città 30?

Data at hand do not reflect the average 10% reduction in car traffic typical in other cities, which may be interpreted as people still being reluctant in abandoning cars in favor of public transportation such as buses.

Q2 — Do people choose to use Bikes more?

Bike usage analysis has shown little correlation with the introduction of new limits, indicating that despite people tend to choose more and more forms of alternative mobility, this might not be encouraged by the new law. In Europe, spikes in bike usage (around 10–20%) appear when new limits are mixed with investment in infrastructures that promote bike mobility.

Q3 — Has the Center been more impacted?

Zones inside the city center have registered a lower traffic both in bikes and cars, indicating that the new limits don’t prevent traffic accumulation in adjacent areas. This aligns with results from the first study, that show how people don’t change significantly their behavior in mobility without other incentives.

Q4 — How has Air Quality changed in the 30-zone?

Air quality has been impacted positively relatively to NO2 emissions, an effect observed in other cities (with a 10 to 20% reduction, usually for PM10 release as well). However, emissions regarding the majority of gases accounted for do not register significant changes; this is an encouraging result, but gases are still well above thresholds imposed by EU and WHO laws.

We believe that Città 30 has marked a new way of thinking life and mobility city to Bologna, indicating a new attention in quality of life and environmental issues. This provision, however, is only a dent in the system that prevents change. Only by continuing the effort in reshaping citizens behavior and providing sustainable alternatives a real impact can happen.

CREDITS
members and roles

Ludovica Benini

Data analysis & visualization on air quality and EV usage; webpage development & styling.

GitHub: github.com/qwindici

Alberto Ciarrocca

Data analysis & visualization on bike usage; webpage development & styling.

GitHub: github.com/vattelalberto

Niccolò Molinati

Data analysis & visualization on car usage and 30/non-30 comparison; Figma design & storytelling.

GitHub: github.com/NiccoloMolinati

PLEASE Open on a Desktop Computer <3