This is the number one issue in resident surveys. We have tried Speedwatch, Speed Indicator Signs but we have always had speeding as an issue.
20 MPH is too fast in any case some speeding takes place a couple of metres from the front doors. We have put several 20 MPH signs around the estate in an effort to remind people. We advocate driving at 10 MPH or less, then anyone following has to do the same.
The road design with no road markings at junctions and tight right-angle corners is supposed to encourage lower speeds. It does for most drivers but alas not everyone.