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Why do drivers speed?
They speed because of their responsibility to safety. Yes really. Read on.


Why do drivers speed? Is it the height of arrogance - they think they know better than the experts? Is it utter contempt for life and property? Are they are just selfish, irresponsible and self-important? Or is there something much more subtle and important going on?

Some recent data

Every year the Department for Transport publishes a report called "Vehicle Speeds in Great Britain". A new version has recently been released and carries speed survey data from 2003. Here are some of the headlines:

  • 57% of cars were exceeding the 70mph motorway speed limit
  • 9% of cars were exceeding the 60mph single carriageway national speed limit on rural roads
  • 58% of cars were exceeding the 30mph built up area speed limit
  • 27% of cars were exceeding the 40mph built up area speed limit
If drivers set their speed to "speed limit+x" as some seem to claim, we would expect the proportion exceeding the speed limit not to vary with road type. Clearly since 57% is very different from 9% things are not so simple. 

It is also highly notable that this "speeding behaviour" is more or less unchanged from earlier years' speed survey data. With a massive growth in speeding convictions by camera year on year how on earth can this be? Are drivers mad? Don't they care if they get caught? Or is there a very good reason for their behaviour?

Safe Speeds

Safe Speed believes that there's a very simple and very important reason why so many drivers exceed the speed and why their behaviour is has proved to be so very difficult to change.

A clear and powerful message...

Drivers fulfil their duty to road safety by selecting a safe and appropriate speed according to the conditions. The message from the conditions is so clear and powerful to experienced drivers that choosing a slower or a faster speed than that dictated by immediate conditions actually feels wrong.

In fact, setting an appropriate speed, and reducing it when necessary is the essence of safe driving.

There are only two parameters drivers can affect to alter the movement of their vehicle - they can alter course or speed. Speed is closely related to safety because when there's an obstruction ahead, and there often is, if you are going too fast to stop you crash every single time. The simple fact that crashes are rare - very rare indeed compared with vehicle movements - is absolute proof that drivers are very good at setting safe and appropriate speeds. It's very rare for them not to be able to stop in time.

But wait a minute - didn't we just say that "speed is closely related to safety"? We did, and it is, but this is absolutely not the sort of speed that you can measure in miles per hour. This is exclusively "speed appropriate to the conditions". 

But suppose we managed to replace drivers choice of speed with blind adherence to speed limits? It would take a very brave or foolish man to assure us that drivers would still be as effective at: "slowing down when necessary". And if drivers become less effective at slowing down when necessary they will crash more often. 

The nutters

We undoubtedly have a minority of reckless individuals who speed dangerously as a result of disregard for the safety of themselves or others. These individuals are dangerous and are well deserved of the attention of the Police. Let's hope they can be identified and dealt with. Safe speed deplores the misuse of speed. But I expect everyone will agree that we're talking about considerably less than 10% of the population. So what about the rest of us?

Risk factors

We have about 32 million drivers. What are the risks of various accident types?

Accidents: per annum average risk of causing:
Damage only accident 3,000,000 1 accident in 10.6 years
Slight injury accident 221,751 1 accident in 144 years
Serious injury accident 30,521 1 accident in 1,048 years
Fatal accident 3,124 1 accident in 10,243 years
Speeding related fatal accident (high estimate) 312 1 accident in 102,564 years

So despite the typical driver exceeding the speed limit on almost every journey, he will be able to go over 100,000 years before he causes a "speeding related" fatal accident.

Does this sound like the dangerous use of speed? You have seen the films on TV of joyriders in stolen cars blasting through town centres at 90mph. That really is a dangerous use of speed. But guess what? The reckless joyriders are included in the figures. The boy racers are included in the figures. The high speed drunks are included in the figures. The young and inexperienced drivers are included in the figures. The unlicenced and underage reckless drivers are included in the figures. Even the born again bikers are included in the figures.

If you are a normal responsible motorist who regularly exceeds a speed limit, your chance of causing a speeding related fatal accident is probably 1 such accident in 200,000 years. This doesn't sound like the expected results of reckless behaviour does it? So much so that we can say for sure that it isn't reckless behaviour.

What about the speedo?

If you had no working speedometer, could you drive safely over an extended time period (say many months)? 

If you could drive safely, what does that tell you about the real importance of the speedometer and the numbers it shows?

As we say at Safe Speed: "You can't measure safe driving in miles per hour." You can't measure safe speeds in miles per hour either.

The excuses

It isn't by any means obvious that driver behaviour in terms of speed is actually driven by safe speed behaviour and if questioned about "speeding", drivers often reply with excuses including:

  • I didn't know what the speed limit was 
  • I was just keeping up with the traffic 
  • The speed limit is outdated. Vehicles are safe at higher speeds these days 
  • I was in a hurry / late for work / late for appointment etc. 
  • The speed limit is too low
But these are just excuses. Very few drivers are actually breaking the speed limit carelessly or recklessly. They are simply doing what drivers do best, and that's driving at a safe and appropriate speed for the conditions.
Deadly speed

Drivers are licenced to use deadly speed. The clear proof of this is that at least 95% of accidents take place within the speed limit. Make absolutely no mistake. The lowest widespread speed limit is 30mph and 30mph is a deadly speed. 

30mph is a deadly speed

In fact, in an impact with a pedestrian at 30mph, research warns us with utter clarity that 50% will die. This claim is frequently repeated in support of speed camera policy and comes from "Ashton and Mackay, 1979 (graph of main findings)". We fully accept their findings)

However, because drivers do reduce their speed in areas of danger and before impact, 2002 figures show that 37,270 pedestrians were injured in impacts compared with 572 who were killed. The proportion who did die was 1.5%.

Clearly if they had been struck at 30mph we would have expected over 18,600 to die. Drivers reducing speed clearly saved over 18,000. 32 times the number who died. 

(from RCGB, table 24, 2002 figures, pedestrian impacts in built up areas, 30 and 40mph speed limits (link))

If we are to trust drivers to mitigate their deadly speed to avoid accidents, the actual number of the speedometer is of little relevance. 

Millions of accidents each day are prevented because drivers have reduced speed when necessary. It is this: "reduce speed when necessary" behaviour, exhibited to excellent effect by drivers everywhere, that is the foundation of our entire road safety system. 

If drivers are inherently trusted to reduce speed when necessary, then there is little reason why we need to set numerical speed limits for them in general at all. The groups that need numerical speed limits are the novice few and the reckless few. The rest of us are very good indeed at setting appropriate and safe speeds both above and below the speed limit as necessary. We know we're fine at it, and we do it daily. Safe Speed believes that typical drivers' speeding behaviour is a manifestation of this crucial safe speed behaviour.

Some claim that drivers in general cannot be trusted to choose their own speed. They claim that speed limits are necessary to prevent drivers from using speed dangerously. But drivers all use deadly speed legally. They are charged with the responsibility of using deadly speed wisely and the rarity of accidents proves beyond doubt that the vast majority are well up to the challenge.

Speed limits have traditionally been set at the "85th percentile of traffic speed under free flowing conditions". This has been official recognition of drivers' safe speed behaviour. (see: Speed Limits)

Are drivers perfect?

You may have formed the impression reading this page that we think drivers are perfect. Nothing could be further from the truth. We think the average (arithmetic mean) driver is a long long way from perfect. He uses safe speed behaviour, but not well enough or frequently enough and his failings are responsible for over 200,000 injury accidents each year.

What we do have is a really good start on a fine road safety system based on driver behaviour. Our drivers are the best in the World at avoiding accidents, but they could still be far far better. Changing the road safety system by improving drivers is a really really good idea. Present policy seems to be changing our road safety system for the worse by emphasizing the wrong things and distracting everyone from setting appropriate speeds and observing the road ahead.

Our road safety system is a huge thing with masses of inertia and the best we can hope to do with policy is to give it small nudges. We just need to be absolutely certain that we are nudging it in the right direction.


Safe Speed believes if we actually managed to stop people speeding and they drove by the speedo instead of by the conditions we would see a massive increase in the death toll. 

Safe Speed believes that drivers must exhibit "safe speed behaviour" if they are to be successful at avoiding crashes. 

Safe Speed believes we could make drivers more successful at avoiding crashes if we make "loud noises" about the value of safe and appropriate speed. 

Safe Speed believes that the current "loud noises" about speed limit compliance is actually reducing the safe speed behaviour on which our road safety depends. This is one vital part of the jigsaw that explains why neither fatalities nor speeds are falling in the speed camera era.

Further reading

What do we mean by speed?
What should we do about speed enforcement?
Speed limits and the 85th percentile speed?
How the rules for speed camera placement miss the point.


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End the obsession with numerical speed NOW!

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Copyright © SafeSpeed 2004
Created 28/05/2004. Last update 18/11/2004
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