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:
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:
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:
There is so much more in the article, I suggest to read it fully.
crossposted from: https://mastodon.uno/users/rivoluzioneurbanamobilita/statuses/114827312307353297
Are there "things" around the road? Houses, workplaces, industrial estates, parks? If so, there will be people walking and cycling on the road, and the speed limit should be 50 (or ideally 30). If it's just a road in the middle of nowhere, sure, make it 80/100 depending on how well you can maintain it.
Nope just fields of grass and some trees that are far away.