If you're in the UK, you'll recognise this catchy little bit of original thinking as part of the witch-hunt the authorities are waging against drivers. That's not to say there's anything wrong with the Twenty's Plenty idea (the aim is to get everyone to drive at 20 mph in 30 mph zones for safety reasons), just that the concept of the whole plan is flawed in that it concentrates on the premise that speed itself is dangerous, rather than the the reality that a speed inappropriate for given circumstances is dangerous. This concept fosters the prevailing notion amongst the majority of 'non-thinking' drivers (who only drive to get from A to B), that the posted speed limit on any road is the speed to be travelled at (rather than the limit), since it has been blessed on high by the authorities. They don't think, and adjust accordingly if there are kids or people on the road, and they're the reason the Twenty's Plenty scheme came into being.
I have a wonderfully daft example of this scheme on my own doorstep now. Many of the streets around my home have sprouted these signs, which is fair enough. There are however, two problems. The first is the fact that they are advisory, and have no legal standing as speed limits – the figures appear on a white background within a green circle. Legal speed limits must appear within a red circle. In other words, they'll be ignored and mocked by those who really need to heed their advice. The second problem is that they've mainly been installed on side roads, avenues and crescents, most of which you'd be lucky to reach 20 mph in, let alone the permitted 30 mph as they are between 50 and 100 metres long. It gets better…
There is some justification for installing these signs, as there is a primary school nearby. There's just one tiny problem. None of these signs are currently installed on either (it's on a corner) of the roads that run directly past the school. And, those roads are around 300 metres long, one being particularly narrow and twisty just as it reaches the school. Also, despite markings to the contrary, doting parent park right up to the gates, so they can pick up their offspring. Actually it's quite safe in reality, as this reduces the road to a single lane if they park on the school side of the road, or blocks it completely if one genius decides to stop and wait in it rather than sit in a side street if they're too late to get a prime spot.
There's going to be a part 2 to this story later, just as unbelievable as this one.