Does the 30km/h speed limit in the city increase air pollution? Let’s clarify

In recent days, there has been much discussion in the media about a study presented by Professor Charles Ratti (founder and current director of the MIT Senseable City Lab) which reports that the introduction of the speed limit 30 km/h throughout the Municipality of Milan could cause a increase in pollution (e.g. carbon monoxide, carbon dioxide, nitrogen oxides and particulate matter), mainly due to the increase in travel times and the fact that engines are more efficient at higher speeds (70-80 km/h). The result was presented during the third forum of TheUrban Mobility Counciland it is interesting because it goes against the trend of measurements conducted in cities where the 30 km/h limit has already been adopted, such as Paris, Brussels and Zurich: here, in fact, a clear decrease in polluting emissions can be seen. One of the limitations of the MIT study is in fact the fact that it does not take into account the reorganization of the car fleet that would follow the introduction of the limit. The study is nevertheless noteworthy, so let’s try to clarify by analyzing its content in more detail.

The results of the study on the 30 km/h limit in Milan

The study being presented is called Application of telematics data for the definition of urban speed limits. Milan a case study and was led by Umberto EscapesResearch Manager and Partnership Lead at MIT. The data used in this study were collected anonymously through telematic boxes provided to its customers by the insurance agency that conducted the research. Through data analysis, we went on to evaluate theImpact of 30km/h areas on travel times and therefore, indirectly, on Milan’s city traffic.


Specifically, the following have been defined: 9 scenarioswithin which Milan was divided into 4 concentric ringswhere the speed limit has been selectively applied based on their type (excluding primary, primary and secondary roads, etc.).
Taking as a reference an urban journey lasting approximately 16 minutes and 40 seconds, at worst (i.e. application of the limit to all roads in the entire municipal perimeter) it is estimated that 89 second increasebringing the journey to 18 minutes and 9 seconds.

As underlined by the mayor of Milan Beppe Sala, a reasonable application of this limitation would lead to an impact on travel times. between 15 and 40 seconds. Furthermore, the study shows that 66% of trips in the municipality of Milan have an average speed less than 30 km/hin fact the average speed in urban travel is approximately 28 km/h.

The environmental impact of the 30 km/h speed limit

At the end of the presentation mentioned above, the moderator of the event Lavinia Spingardi he noted how the study highlights a correlation between the Driver behavior and CO emissions2. In response Fugiglando intervened by highlighting that the reduction in average speed actually has an impact on amount of greenhouse gas emissions (CO2) and polluting emissions (such as SOxNOx and particulate matter), in particular there would be an increase in CO2 of 1.5% and an increase in particulate matter (PM) of 2.7%.

It should be kept in mind, however, that these studies were carried out considering the current fleet of vehicles in circulation: this means that the effects on micromobility and on how many fewer cars will be needed as a result of a Road Redesignwhich indirectly impact the overall emissions result. The Senseable city lab study will in fact continue by evaluating the positive impact on urban mobility. It should also be noted that the quantity of zero-emission vehicles has a more significant impact, so incentives to replace the most impactful vehicles can also provide additional benefits in terms of emissions.

Obviously, in addition to the issue of emissions, let’s keep in mind that this limit was chosen mainly for reasons of road safety.As detailed within the study Review of City-Wide 30 km/h Speed ​​Limit Benefits in Europethe application of the speed limit of 30 km/h in 40 European cities has significantly reduced road noise, together with the 23% reduction in the number of accidents and, consequently, a 38% decrease in injuries and a 37% decrease in deaths.