This 30/40mph trade-off is re-explained - we've heard bits of it before - in a new road safety commercial: "30 - it's for a reason," it says. It's quite a compelling idea and it gives valetudinarian types something to lecture people about.
But this crisp, necessary point is obscured by the treatment which, in a very fashionable distracting way, involves somebody dead talking to you. From Twin Peaks to Desperate Housewives, taking in Six Feet Under, dead people have become vocal.
Here, the child you have to feature in road safety commercials is a talkative, dead one. At first she's lying at a suburban roadside, very pale with a trickle of blood from her ear, but nonetheless still doing the voice-over: "At 40 there's an 80 per cent chance that I'll die," and so on.
Then - and this is the deeply distracting bit - they put her into reverse. The blood runs back into her ear, she slides into the middle of the road and opens her eyes. It makes you think about the stylisation of the approach, the tellyness of it. And yet it may just work at the level of providing a memorable hook - particularly for people who hyper-register anything involving children.
Road safety advertising needs to work a small budget hard, it needs to be shocking in ways people can internalise rather than reject and it needs to use every trick in the book - like the motorcyclist who collides with an invisible car - while seeming naturalistic. Life can be heightened but, the convention has always been, it shouldn't look like fiction. This commercial takes that risk in a good cause. I'd like to know if it works.