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
So the limit is what matters, but it has to actually be enforced. Thats some very novel insight hmmmm. But yes, physical filters like bumps are much more effective compared to signs.
Not just bumps but designing infrastructure so it forces the drivers to negotiate it at lower speeds.
Simple stuff like narrowing the approach to junctions and roundabouts so it has to be taken at a slower speed than it being a wider aperture when minimal braking is required.
Raising the pedestrian or bike where it crosses a road (on side streets) so the vehicle has to slow rather than the active transport methods.
Reallocating road space to wider pavements and segregated bike lanes so streets are mixed modal.