Thats really terrible and also for you if you were first there. Of course we need to find ways to prevent as much as possible that happening but I still dont think speed bumps are a sensible answer or through roads with a 30 limit, or are you suggesting all 30mph roads should have speed humps at regular intervals.
yeah, I'd done the course recently, I was genuinely trying to watch my speed, but did not see the lowered speed sign.
There is a grace period of 60 seconds when a sign first appears. If it goes from 70 to 40 but the sign has been displaying that in the distance for a while then slow on approach, if it lights up literally as you approach it then it won’t flash for a minute to avoid the scenario you describe.