The Speedo


We have worried consistently over the last few years about the amount of driver attention focused on the speedometer. Is speedo watching a serious road safety issue? We have put in place a crude system to gather data based on our visitor's experience and their results from an experiment. We can then go on to estimate the proportion of total observation time lost due to a typical speed camera installation.

Two critical items of data are not normally available:

  • How long does it take to check your speedo?
  • How many times would you check your speedo in the vicinity of a speed camera?
We have done our best to try to put numbers to these parameters. The results might surprise you.

This page has three associated forum topics

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Speed cameras in hazard zones

It was recently pointed out to us that drivers normally check their speedos "more than once" in the immediate vicinity of a speed camera.

Let's look at a typical example, and see what that might mean.

  • Straight single carriageway A road, 50 mph speed limit. 
  • This camera is positioned 100 yards before a crossroads. 
  • The camera is highly visible. 
  • Traffic is light, it's dry and daylight. 
  • No vehicles are turning or waiting to turn at the crossroads. 
  • The "area of the camera" extends from 100 yards before the camera to the cross roads. 
  • The car is registered to you.
At 50 mph you will be in this (200 yard) area for 8.2 seconds.

If a speedo check takes 1.1 seconds the following table applies:

number of speedo checks percentage of road observation lost
1 13%
2 27%
3 40%
4 54%
5 67%

We think the percentage of observation lost may prove to be very significant and very dangerous.

You can answer our poll question about how many times you would check your speedo in the hazard zone. (click here)

Early results

About three quarters of the respondents say they would check the speedo three or more times in the camera zone. Over 10% say they would check the speedo at least five times.

Experiment: How long does it take to read the speedo?

We have not been able to find any research, so we've devised a quick experiment so you can test approximately how long it takes you to make a speedo check.

Equipment required

  • Clock with sweep second hand (ideally about the same size as your speedo)
  • Window with view to scene more than about 60 feet away


Stand at the window and hold the clock in about the same position relative to your eyes that the speedo would occupy if you were driving. Watch the clock. When the second hand passes 12 look out of the window and focus on an object more than 60 feet away. Immediately look back at the clock to check the elapsed time. Repeat until 10 seconds has passed and count the number complete cycles.


  • average time = 10 seconds / count
  • So for example, if you managed 11 cycles in ten seconds, we would calculate 10/11 = 0.91 seconds per cycle approx

Comments and notes

  • The lion's share of the cycle time is the time it takes for your eyes to refocus. 
  • You may well notice that you can feel the focusing muscles in your eyes doing the work.
  • Younger eyes refocus faster.


If you wish to add your own personal results using this test method, the following Safe Speed forum topic has been set up for the purpose. Remember to give the following data:
  • Complete cycles in 10 seconds
  • Your age

  • Use of the forum requires simple registration. You can (click here) to report your results. Or (click here) to view others' results.

Early results

None of our first few experimenters have reported more than 11 cycles, with about 9 cycles being typical. That would make the typical speedo check just over 1.1 seconds. 

At first sight the figures being generated here are extremely worrying, but what do they really mean, and what else should we be considering?

Mirror checks

Associated with speed adjustment, most drivers will also make a mirror check. That is of course even more attention diverted from the "dangerous" cross roads ahead.

Noticing movement

If you are looking at something when it starts to move, it is immediately obvious that the object is moving. If you look away and then back, and the movement started during the period when you were not looking. there is a finite additional time after you have looked back before you recognise the movement. This might add 0.5 seconds to the effect of a speedometer check.

Perhaps drivers can well afford to look away from the road ahead?

We are sure that there are times when we consciously and properly decide that nothing much is changing ahead, and on that basis decide to do a speedo or instrument check. But the camera zone isn't an "open road", "no hazard" situation. We're approaching a dangerous junction. Surely anything that diverts the drivers attention from the danger ahead is dangerous?

Other attention grabbers

The speed limit and the camera itself probably also get a significant quantity of the drivers' attention.

Grasshopper attention and visual search

It is clearly in the nature of driving that we "look around" regularly.  It follows that our attention is routinely spread rather thinly around the possible objects of interest. We compensate for this effect by working with a series of snapshots, and we ensure that we normally return to each part of the scene before a situation can develop into a danger. So does it matter at all if an experienced driver allows his attention to be diverted to the speedo as long has he does not look away from the scene ahead for too long? We think it's critically important.

How does a speedo check compare with a mirror check?

Mirror checks do not require refocusing because the objects in the mirror are as distant as the objects ahead. Checking the mirror is a vital part of safe driving, but we suggest that checking the speedo is largely unnecessary. We know very well that we can drive perfectly safely without a working speedometer.

Is all the speedo check time lost?

Even if a full speedo check takes one second, during that full second you have seen the road ahead twice and the speedo once. The actual lost time is possibly more like half a second. Even if the half a second turns out to be a better estimate we still think that the average driver - who apparently will check his speedo three times in the example eight second situation - is still giving up about 20% of his total attention to the speedometer. We think even 20% is a massive road safety issue.

Perhaps the big danger comes from "joined up inattention"?

If a driver checks: camera, speed limit, speedo, mirror and speedo again, without once looking ahead, we think most people would agree that a serious safety risk exists. How often do drivers do this? We don't know. Clearly research needs to be carried out. 

Those on 9 points

As more and more drivers accumulate licence points so their obsession with the speedometer can only increase. Those on 9 points may well typically spend more than half their time in the danger zone checking their speedometers. 
Inattention was recently listed as the number one accident contributory factor by the DfT, with inattention recorded in 25.8% of almost 61,000 accidents. Safe Speed has long warned of the danger associated with driver inattention. (click here). This looks like devloping evidence that speed cameras promote inattention in dangerous places.
Be careful what you wish for...

If time spent checking the speedo in camera zones does turn out to be a major safety issue, there are a couple of unpalatable solutions that might be suggested:

Invisible cameras

Naturally if the camera cannot be seen a driver's reaction to it may be considerably different. On the other hand, most drivers use the same routes regularly and would learn where the cameras were. However, The DfT has already decided that hard to see cameras are unacceptable because they are perceived to be underhand and sneaky. Since that decision in 2001 camera acceptability has apparently continued to plummet for other reasons.

GPS speed limiters

We believe that speed limiters that "know" the speed limit are probably the most dangerous idea around in modern road safety. Such limiters take no account of the mechanisms by which accidents are avoided, and the net effect of wide installation would be extremely dangerous. We'd have a nation of foot-to-the-floor zombie drivers, lulled into a false sense of security by the "zombie-safe" speed limiter.
When things go wrong on the road, and they always will, we absolutely depend on drivers recognising the danger and reacting. About 9 times out of 10 these reactions are entirely successful and most potential accidents are mitigated into near misses. In the imaginary world of the speed limiter, would the quality of driver reactions be the same? No, of course they wouldn't.

Head-up display speedometers

A good head up display system would project a speedometer image onto the windscreen where the driver could read it without looking away from the road and without refocusing. This would undoubtedly be an improvement unless it tended to foster and extend the dangerous obsession with numerical speed.

Checking the speedo in a hazard zone because of a speed camera may turn out to be extremely dangerous. You would think that the powers that be would have considered this possibility and gathered proper scientific evidence before embarking on smothering the country with speed cameras, all supposedly in dangerous places.

But there is no scientific evidence. This alone is a scandal of considerable proportions.

Once again Safe Speed has identified a glaring flaw in modern UK road safety. Heads must roll and real road safety must be restored.


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End the obsession with numerical speed NOW!

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Copyright © SafeSpeed 2004
Created 13/04/2004. Last update 14/04/2004