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 𝑝-values in the Mann-Whitney U test. All 𝑝-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

  • Damage@feddit.itEnglish
    0·
    6 days ago

    This is Italy we’re talking about, our public officials want zero responsibility so they always set absurdly low limits.

    Point is, road design is everything, if you want people to go slow, you can make it so, if it’s an area where people can go faster, design the road accordingly and keep it maintained, don’t let it turn into a crater field, just to later “fix” the problem with a temporary speed limit.

    In Milan this would be possible, since it is a rich city, in the rest of Italy, not so easy.

    • balsoft@lemmy.mlEnglish
      0·
      6 days ago

      This is Italy we’re talking about, our public officials want zero responsibility so they always set absurdly low limits.

      Sounds good TBH. If they also narrow the roads/remove lanes to enforce it, put bike paths/public transit lanes in the free space, and fine anyone driving dangerously, then this is the recipe for a good city.

      • Niquarl@lemmy.mlEnglish
        0·
        4 days ago

        I doubt people drive at 80 in a city, that’s a rural setting. Do people drive at eight kph where you live? Fastest is 70 and that’s basically a highway where I live

        • balsoft@lemmy.mlEnglish
          0·
          4 days ago

          I doubt people drive at 80 in a city

          Yeah there are roads with 90 km/h speed limits within city borders. And people speed too. It’s insane.

          Although if you as a pedestrian ever try to cross a line of traffic going 60, it’s also quite horrifying.

          I believe the speed limit within cities should be 30 km/h by default, with very few exceptions. That puts people before cars, as it should be. And ideally we should strive to make public transit and bicycle infrastructure good enough to just ban personal vehicles in cities outright.

          I say that as someone who owns a car and likes driving it. Cities and towns are just not the right place for cars. They belong on dirt country roads and off-road. Basically, if the population density allows us to build serious infrastructure for transportation, it doesn’t make any practical sense to build infrastructure for personal motor vehicles.

          • Niquarl@lemmy.mlEnglish
            0·
            4 days ago

            That’s a lot more than just putting signs up saying 30kph however. You’re talking about a radical change