20 mph involves some paperwork = road traffic regulation, some public awareness and some signage.
It needs some extra effort on enforcement though (at least the threat of random speed checks or mobile cameras) otherwise a 20mph limit just means many people do 40mph+ because there's going to be very little chance of being caught. It depends how much you read into the Police attitude to enforcement of 20mph limits.
Anecdotal but I see this on some roads near me that have been made 20mph. The residential area I live in is mostly OK but on roads like Putney Heath (from The Green Man to Roehampton) that have gone from 30mph to 20mph and whilst average speeds may have gone down, I'm sure the number of people doing more then 40mph has increased.
It needs some extra effort on enforcement though (at least the threat of random speed checks or mobile cameras) otherwise a 20mph limit just means many people do 40mph+ because there's going to be very little chance of being caught. It depends how much you read into the Police attitude to enforcement of 20mph limits.
Anecdotal but I see this on some roads near me that have been made 20mph. The residential area I live in is mostly OK but on roads like Putney Heath (from The Green Man to Roehampton) that have gone from 30mph to 20mph and whilst average speeds may have gone down, I'm sure the number of people doing more then 40mph has increased.