Safety matters at 80mph

Speed limits are in the news today, as the Tories want to raise the top speed on motorways to 80mph. And, as ever with talk of cars, there’s barely any mention of safety. We’re told that brakes have improved since the limit was set in the 70s, so it’s fine. This isn’t good enough.

The kinetic energy of a car at 80mph is 30% higher than that of a car at 70mph. Sure, brakes may be better, but what happens when there’s no time for brakes? How do safety systems in cars scale to those energies? What about central reservations? If all else fails and you hit something at 80mph, what difference does that 30% make to the physical interactions that occur, and how these present a danger to anything nearby? Maybe all these things are fine, and 80mph is safe. But maybe they’re not. This deserves a higher priority in public debate. I reckon this never happens because drivers seem to think you can intuit road safety simply by being a driver, which you can’t.

For example, a common moan is people whining about low speed limits on straight roads. What possible reason could there be? It’s a straight road! Here’s a reason: you can’t properly judge how fast an oncoming object is approaching. Nobody can. Ever seen somebody walking in the distance, and not been able to tell whether they’re moving towards you or away from you? That’s because a person walking directly towards you looks very much like a person walking away from you, and the percentage difference in distance isn’t enough for the brain to figure it out. And once our brain has even worked out which direction they’re going in, all it has to work with is a dot on the visual field slowly growing larger. The human brain sucks at judging the speed of things coming directly towards you. It doesn’t matter whether you’ve been driving a day or 30yrs, you’re still crap at it. Every time
you overtake someone, and you’re surprised at quite how quickly that oncoming car approached? That.

So – the straight road. If you decide it’s safe to do 60, and overtake the moron doing the 50 limit, and there’s someone coming the other way also doing 60 who approaches way faster than you expect, then that’s a 120mph collision that takes out both drivers, any passengers, and probably the car you were overtaking. But the slower you’re going in the first place, the more time you have to react to these kinds of situations. So that’s a good reason, without even looking at the particular environment – what if the road runs east/west, so twice a day has people driving directly into the sun? There are a thousand factors.

Road safety is complex, and counterintuitive. I’ve read just one book on the subject, and it blew my mind. It’s the domain of experts. Nobody’s taught about the visual field’s inability to judge oncoming speed, so we inherently have to rely on the experts who keep us all safe. And there are decades of studies on road safety – which you’d hope, given the thousands of people that die on the roads every year. But did anyone on Question Time talk properly about road safety this evening? No – one mention of ‘brakes are better’ and the discussion moved on to the economic benefits. Hooray.

It’s remarkable enough we’re allowed to drive 1ton metal monsters at speeds high enough to kill somebody in the blink of an eye. But that we’re allowed to do it without even a vague understanding of why the rules exist? Insane. If you’re on the roads, the very basic, minimum moral requirement is to stick to the rules created by people who know infinitely more about the topic than you do. Yet, safety is just a quick aside for the politicians wanting a crowd-pleaser. Ugh.