Opinion: Understanding the impact of speed

By Mark Cartwright, head of commercial vehicle incident prevention at National Highways and lead at Driving for Better Business I want to talk to you about speed. No, don’t switch off – it’s really interesting, and I want to share something I learned recently that blew my mind.

Take two identical cars – but one blue, one red – with identical drivers and the same road conditions. The blue car is being driven at 70mph, the red at 100. As they are exactly alongside, both are heading for a static obstruction and both drivers react immediately, braking as hard as possible.

The blue car, originally going at 70, stops just in time. What speed is the blue car vehicle doing when it reaches the object?

30mph?

20? In fact, it’s 71mph.

Seventy-one miles per hour! After braking as hard as possible, the red car is still travelling faster than the blue one was at its initial speed – except the blue car is now safe and stopped. The red car hits the stationary object at 71mph.

If you still need convincing, take a look below. [embedded content] The problem about losing momentum is not linear: you don’t stop from 100mph at the same rate as you would if you were doing 70.

We need to change how we think about braking: we so often talk about how long it will take us to stop. We need to be much more aware of the seemingly disproportionate effect even a few extra mph makes to the speed of impact if we don’t manage to stop. It could easily make the difference between life or death.

That’s why there’s been so much focus recently on taking speed limits down from 30mph to 20mph where there are other people – driving, riding, walking to school, taking the dog out, shopping – and why Brake, the road safety charity, focused this year’s annual Road Safety Week on speed. In the fleet world, of course we need to meet customers’ demands, but who would agree to a driver breaking the law to do so? What if we can see, via telematics data, when drivers are doing this and maybe turning a blind eye if it’s ‘only a few mph over’ or if that person is a star performer or even the boss?

And how will someone respond to having their driving criticised? In the UK there is no real evidence that going more slowly takes longer. We perceive that we get there quicker but actually, fleets that speed limit HGVs below 56mph (to 53mph for example) find that journey times are no longer.

Why? Because in this country, we don’t have hundreds of miles of open road in which those speed increments make a difference: we have junctions, and congestion and traffic lights. Theoretically, driving at 40mph in a 30mph area for 14 miles could ‘save’ us 7 minutes.

On a motorway, driving at 80mph instead of 70mph ‘saves’ you 90 seconds over 14 miles. And a van will use 20% more fuel at 80mph than at 70mph. There’s a lot to be said for the hare and the tortoise approach: consistent, steady progress beats the pressure of heavy acceleration and braking – all of which means wear-and-tear on the driver, the vehicle, the road, and all the other road-users around.

Everyone understands that it’s unsafe to drive down a narrow, residential street at 90pmh. We see those drivers as reckless. It all gets a bit hazy when it’s ‘just a little’ over the limit.

We think: everyone else is doing it, where’s the problem? But let’s not kid ourselves: the risk of injury or fatality goes up with every mile per hour over the limit, just as the distance it takes us to stop. Chief Constable Jo Shiner put it like this: “Discussions about speeding, and in particular the way in which the police enforce the law on speeding, often descend into arguments about being ‘just a little bit over the limit’, or the speed camera location, or whether drivers were properly warned in advance of a speed detection operation.

“We don’t have these sorts of conversations about being ‘just a bit’ over the drink-drive limit or driving a ‘little bit’ dangerously. I know that with alarming regularity staff operating speed camera vans at the roadside are verbally abused and berated by passing motorists. All of this ‘noise’ misses the uncomfortable and inescapable truth that speed kills.

“Unlike any other crime, road users are both potential victims and potential offenders every day. Abiding by the laws of the road, which are designed first and foremost to protect life, reduces the chances of being killed or seriously injured in a collision or causing a fatal or serious collision.” Personal responsibility is the starting point for safer roads.

It starts with every one of us, and our drivers.

For 2024, let’s pause and reflect if we’re putting drivers under pressure – and putting everything else at risk in the process.