BBC report a study showing a decline in RTCs both before and after the urban speed limit was mostly reduced to 20 mph in Edinburgh: https://www.bbc.co.uk/news/uk-scotland-edinburgh-east-fife-55863412.
The rate was already falling, but there's apparently an increase in the rate of decline and a cultural shift. And if the RTCs are at lower speeds, they become more survivable.
When the limit changed, initially it was ignored. There was a little bit of enforcement, and I think over time 33 mph as a norm has fallen to about 25. I've not been hooted at doing 20 in the car* although a queue does tend to form behind me. So perhaps there really has been a change. I am going to email one of my ward councillors who is sympathetic to cycling to encourage more action, and perhaps this example can help persuade others.
*Sadly not enough data to draw a conclusion from doing 20 on the bike...
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