this post was submitted on 10 Jul 2025
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30 km/h limit data analysis shows that what matters for compliance is not the limit, but the features of the streets (from OSM data) (senseable.mit.edu)
submitted 2 days ago* (last edited 2 days ago) by [email protected] to c/[email protected]
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This study from MIT used geo data collected from cars in Milan, Italy, to check the effectiveness of 30 km/h zones in reducing speed.

The first conclusion is that the signs don't work: 85 percentile speeds are all over the place in 30 km/h zones in Milan, as shown in the figure below:

85th percentile speed profiles of the 30 km/h zones in the City of Milan.

The second step was finding correlations between speeds and street features extracted from openstreetmap. Results are as expected: narrow, short, curvy sections correlate with lower speeds, as do 1 lane vs more, one way vs 2 ways:

OSM features comparison between high and low compliance Zones 30. We report the features with the lowest ๐‘-values in the Mann-Whitney U test. All ๐‘-values are below 0.001.

The final step is also interesting: the authors made a model to predict the compliance of 30 km/h speed limit on streets that are 50 km/h at the moment. Useful for urban planning to understand if charging an area to 30 km/h would need structural interventions (like bumps, narrowing of the street...) or not:

Predicted speed 85th speed percentile with city-wide adoption of limit at 30 km/h

There is so much more in the article, I suggest to read it fully.

crossposted from: https://mastodon.uno/users/rivoluzioneurbanamobilita/statuses/114827312307353297

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[โ€“] [email protected] 7 points 2 days ago (1 children)

I feel like this is a misleading title. The findings talk about speeds, not accidents, noise pollution and quality of life.

[โ€“] [email protected] 6 points 2 days ago (1 children)

The title doesn't mentions accident ts either, but I added "for compliance" to be more clear

[โ€“] [email protected] 5 points 2 days ago

Thanks, this makes it much clearer!

[โ€“] [email protected] 4 points 2 days ago

Lol I mean it's Milan. Over there they honk at you if it takes you more than 0.001s to press the accelerator after a green light.