So, raising the speed limit on UK motorways to 80mph is a good thing, right?

The UK government are reportedly considering raising the speed limit on motorways from 70 miles per hour to 80 miles per hour.  Is this a good idea?  We asked NIReS Director Professor Paul Younger for his thoughts on the subject.

So, raising the speed limit on UK motorways to 80mph is a good thing, right?

Wrong!

The government’s proposal to raise speed limits on motorways to 80 mph flies in the face of their stated aim to significantly reduce our carbon emissions.  Even the USA recognises a need for restraint in highway speeds for the sake of fuel efficiency – which is the same thing as lowering carbon emissions.

But a maximum speed limit is just that, isn’t it? A maximum – it doesn’t mean people have to do that speed.

True, but drive on any motorway (or major road) in the UK (and most other countries) and you will soon find that, in practice, speed limits tend to be treated by many motorists as an instruction on what speed to drive, or in many cases as if it were a minimum speed limit. So, in truth, raising the maximum speed limit on our motorways to 80mph will have the effect of raising a lot of drivers’ speed beyond that level.

This will then increase their carbon emissions not only as a result of this increased speed but also as a result of the way in which they will be increasingly forced to drive.  Aside from those motorists who may not feel comfortable driving at this higher speed, we will still have vehicles on the road whose speed is physically restricted, such as delivery lorries.

In order for more ‘speed hungry’ motorists to be able to maintain their (now higher) preferred speed while avoiding these other vehicles, they are likely to have to brake and accelerate even more often than they currently do, which reduces fuel economy (and therefore increases carbon emissions) drastically.

Can’t these slower vehicles have their maximum speeds increased in line with the proposal, say to 70mph instead of 60?

That question assumes that the only factor dictating the speed of these vehicles is the relative speed of other vehicles on the road.  In reality, these maximum speeds are set primarily to mitigate the physical limitations of these vehicles.  In the majority of cases, vehicles with speed limiters fitted are high-sided vehicles prone, particularly at high speeds, to be badly affected by side-winds.  This won’t change, whatever the speed limit, and the faster these vehicles go, the more precarious their stability becomes.

But suppose I’m driving on a stretch of motorway without any lorries or other speed-restricted vehicles on it. Why shouldn’t I be allowed legally to drive at 80mph?

Well, let’s look at the motorway itself.  In 1965, when a national speed limit on motorways was first introduced, 70mph was judged to be a safe speed limit.  This was calculated taking into account such factors as sightlines and stopping distances, impact of different common weather conditions on visibility etc.

Since then, all new motorway and ‘A’ development has been based around this speed limit: the actual construction, layout and route of these roads have been designed based around the need to ensure adequate sightlines, provision of adequate reaction times in motorists and visibility at 70mph.  To raise the speed limit safely would necessitate significant investment in the motorway infrastructure to ensure that motorists still had sight of enough of the road ahead to be able to react in time at 80mph to avoid incidents or other obstructions ahead.  As things stand, our motorways simply are not designed for safe travel at this higher speed.

But cars are so much more advanced than they were in 1965: aren’t the speed limits out of date for the technology now available to us?

This is an argument which is commonly cited in favour of raising speed limits on roads, and not just motorways, across the country, but fails to take into account one important factor.  While it is true that cars are more advanced than they were in 1965, human beings are not!  Reaction times in the average driver are still the same (and drivers often have more information and potential distractions being thrown at them than in 1965), range of vision of the average motorist remains the same and the level of damage caused by accidents to those unfortunate enough to be caught up in them is very much the same!

What do you think? Are you in favour of the proposed increase to the speed limit or against? Tell us why.

Professor Paul Younger

Professor Paul Younger, Director, Newcastle Institute for Research on Sustainability (NIReS)

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3 Responses to So, raising the speed limit on UK motorways to 80mph is a good thing, right?

  1. Anne Buckle says:

    Will slip roads need to be made longer as well? They’re designed to allow a motorist to build up sufficient speed to be able to join the flow of traffic smoothly (or slow down sufficiently when coming off a road) and presumably, if that traffic is moving 80mph rather than 70mph, you would need more road in order to reach that speed safely?

  2. Professor Paul Younger, NIReS says:

    Yes indeed. And there are already too many places along our motorways where insufficiently long sliproads lead to misjudgements by drivers resulting in accidents. That can only get worse if the speed limit is raised.

  3. Edward Byers says:

    This is a great post that strongly contests the arguments without even drawing too much into the environmental problems that an 80mph speed limit would bring. I found the one concerning behaviour and forcing other unwilling motorists to drive faster also very interesting.

    But lets explore some of the environmental ones in more detail!

    The point about fuel economy is most crucial. We know the relationship with speed and fuel consumption (GHG emissions) is not linear – engines are designed to run optimally at about 55mph – beyond that there is decreasing efficiency coupled with additional air resistance.

    Higher speeds will also mean more tyre and brake disc wear, so more wastage there.

    Apparently this is justified economically by the time savings made – but what certainty is there about rising fuel prices? At what point will the cost of additional fuel expended not be covered by the time-savings?

    Surely the biggest economies are to be made for freight. I find it hard to imagine how me saving a few minutes of my journey will boost the economy. But will freight vehicles be allowed to increase their speeds too?

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