Change one law, make the roads safer?

Politicians like gimmicks, its easier to sell them to electorates via conference soundbites than it is to come out with real changes or real policies. So I've been wondering, is there a 'one thing' type gimmick that would give us real, sound improvements in cycling and walking? I think that maybe there is, so I'll put it out there and see whether anyone agrees. Or has a better idea...

If you're driving, you're driving. And thats what you're doing. You can't faff about with the radio, or the sat-nav, or fiddle with an e-cig, or mess about with your phone or a delivery sheet. You can't eat a sarnie or a bag of crisps, or balance a mug of coffee while at the wheel. Drive or do something else.

Penalty for multi-tasking driving? 6 points. So you can get away with it, once.

Seriously, I think this idea is a go-er. Its easier to enforce (how often have you seen a driver visibly doing something?), its simpler, and it would have a big impact on driving culture - it would bring into focus the fact that driving is something that carries a fair whack of responsibility. Even a small car is a powerful machine that can, if carelessly handled, cause immense harm. We still kill thousands on our roads every year, many of them through simple inattention. While we're not going to make every motorist suddenly give a damn and start looking where they're going, oughtn't we find ways of removing some of these distractions?