My general experience of 20 zones is cars just belting along between whatever traffic calming measures they've put in place to slow the traffic down at which point the cyclist they've sped past then has to slow down because there's a car blocking them from going through the traffic calming at their full speed.
Personally I quite like 20 zones. You can hold primary at 20mph and generally not care about slowing the cars behind you as you're on the speed limit. For the theoretical granny on a dutch bike, small child cycling to school, etc though then it's not much help. They can't hold 20mph out in primary so it makes little difference.
My general experience of 20 zones is cars just belting along between whatever traffic calming measures they've put in place to slow the traffic down at which point the cyclist they've sped past then has to slow down because there's a car blocking them from going through the traffic calming at their full speed.
Personally I quite like 20 zones. You can hold primary at 20mph and generally not care about slowing the cars behind you as you're on the speed limit. For the theoretical granny on a dutch bike, small child cycling to school, etc though then it's not much help. They can't hold 20mph out in primary so it makes little difference.