Statistics

On the news last night, there was a story about how rural roads are more dangerous/deadly than motorways (which just makes sense to me – of which more in a minute) and one of their illustrations of this was this road sign

This is supposedly a sign from “one of the more dangerous roads” – but 43 injuries in 3 years equates to 14 (point 3-recurring) deaths a year. That’s just over one a month. Not quite such a scary figure…  The same goes with 4 deaths in three years – just over 1 a year.

I don’t know if my viewpoint is a rarity, but I look at a statistic like that, and tend to think “I’ll go with those odds”.

And now, about those stats in the first place…

The stats in the story are :

• 3 people a day die on rural roads
• That’s 11 times more deaths than on motorways

To me, that all makes sense, for a number of reasons – including…

• On motorways, people drive faster – but (in general) pay more attention when doing so. Sure, there’s still idiots – there’s idiots everywhere – but in general people are paying a bit more attention on motorways.
• People definitely pay less attention – and drive worse – on non-motorway roads.
• But also – on motorways, everyone’s going in the same direction. It’s *far* harder to have a head-on collision at speed on a motorway.
• The speeds are higher, but with everyone going in the same direction, it also reduces the relevant impact speed. A head-on is the sum of the two impact speeds – so two cars hitting head-on at 60mph is an impact speed of 120mph. Even if you’ve got someone at 70 on a motorway hitting a stationary vehicle, that’s an impact speed of 70.
• It’s not the same factor if you were to crash into someone ahead of you (for example) because they’re still going forward at 60-70mph anyway, so – as I understand it – if you’re going 70mph, and hit someone going at 60mph, the *impact* speed is 10mph – the difference, rather than the sum.

The other key factor is that I’m willing to bet that there’s one hell of a lot more miles of rural road in the UK than Motorway. In 2005, the DfT’s report said that the UK has 2,202 miles (3,523 km) of motorways.  According to this document, the UK’s motorways account for 1% – ONE PERCENT – of the total road space/distance.  So again, 11 times more deaths on roads that account for 99 times the road mileage.

All told, it’s just bad stats and shitty journalism