We should be doing this in Melbourne.
Default speed limit in Melbourne should be 30km/hr unless otherwise signed. The effect on journey times will be unnoticeable.
Ask your car what your average speed is. It's already going to be around 30km/hr unless you regularly travel long distances on rural roads.

#ThanksFor30 #Melbourne #30kmhSpeedLimit

https://www.walesonline.co.uk/news/wales-news/wales-20mph-speed-limit-working-27779212