For more detailed information: https://www.gov.wales/introducing-20mph-speed-limits-frequently-asked-questions
They’re not just lowering the speed limit. From the FAQ:
Will the roll out involve money being spent on speed bumps?
There is no plan to include traffic calming (including speed bumps) as part of the change to speed limits. There are other ‘softer’ measures that might be introduced, such as using buffer speed limits, removing the centre line, narrowing the carriageway visually, using planting etc.
Technically, they aren’t doing anything. This is “just” an announcement if you’re going to be pedantic.
Waterloo, Ontario, Canada is going through a similar process of lowering speed limits in residential areas. The planning staff said they needed the speed lowered so they could implement these traffic calming measures, otherwise the speed limit would be higher than the street design can accommodate. Obviously, the devil is in the details, but it’s a good and important first step.
