/ Motoring

What if your car’s speed was automatically limited?

25mph speed limit

The EU is toying with asking car makers to fit speed limiters to new cars. This could automatically slow down your motor if you tried to exceed the speed limit. A step too far or a helpful road safety measure?

So how would these speed limiters work? The technology, known as the Intelligent Speed Adaptation scheme, would either use cameras in cars to read road signs, or GPS satellites to automatically send the local limits to cars.

You’d then either be warned of the speed limit, or your car’s brakes would be put into action should you get close to driving over the limit. The rules could even require speed limiters to be retrofitted to existing cars.

The EC’s Mobility and Transport Department is consulting on whether to roll out the technology in order to cut EU road deaths by a third by 2020. That’s down from the current 30,000 yearly deaths on EU roads.

However, Transport Secretary Patrick McLoughlin has said that he’ll oppose these plans, stating that Britain has one of the safest road networks in Europe. UK road deaths are apparently at their lowest levels since records began in 1926. A government source said:

‘It is definitely something that [Patrick McLoughlin] is keen to resist and he has told officials that it is something we don’t want to do. To be forced to have automatic controls in your car amounts to Big Brother nannying by EU bureaucrats.’

Could speed limiters create new safety issues?

Introducing speed limiters could cause new problems according to the AA:

‘It could take away people’s ability to get themselves out of trouble with a quick burst of speed, such as in overtaking situations where the capacity to accelerate can avoid a head-on collision.’

With the way technology is going, many of us might be travelling in driverless cars in the future, where our speed is automatically regulated in car convoys anyway. Is that a future you’d like to see? And as for speed limiters, would you consent to having your car fitted with one?

Should cars be fitted with speed limiters to automatically control your speed?

No (66%, 309 Votes)

Yes (30%, 142 Votes)

I don't know (4%, 17 Votes)

Total Voters: 468

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I cannot think of many occasions when being able to exceed the speed limit would have helped me get out of trouble, but I do concede that it should be possible to override any speed control system.

I would welcome testing automatic control of maximum speed because constantly having to keep an eye on my speed and trying to work out the speed limit on certain roads is, I feel, a diversion from other aspects of safe driving.

My suggestion is that trials are conducted, so that we can see if automatic speed control makes a significant difference to road safety. It does concern me that drivers might be encouraged to drive at the speed limit rather than the appropriate speed for the prevailing road and traffic conditions.


I’ve been driving for 45 years and, since driving has frequently been a requirement of my job, I estimate that I have driven over three quarters of a million miles in that time. I’ve always had a penchant for fast cars and have owned a couple of ludicrously fast cars in my life.

Yet I can remember only one, yes only ONE, occasion where a fast car has got me out of trouble. Even then, I was still below the speed limit.


A few years ago, I came up behind a car travelling at a speed well below the speed limit and decided to overtake it. Halfway through the procedure, the car (being driven by a young girl) increased speed to a significant extent and I was obliged to accelerate quite hard in order to complete the manoeuvre
safely. Of course she should not have accelerated while being overtaken but the fact is that she did do so but I managed to accelerate out of danger. It does happen.



Why were you OBLIGED to accelerate quite hard?

Surely you had the OPTION to slow down and drop back in behind the young girl’s car. Taking this option is safer for you, safer for other road users, legal, more economical and SENSIBLE.

Or are you the macho, competitive type who will never be beaten?


Under the circumstances, completing the operation was the least risky option, for two reasons. Firstly, even if I had braked, there was no longer any remaining gap of sufficient size to pull back into safely. Secondly, there was other overtaking traffic behind me, which would have been surprised by sudden braking on my part, when the road ahead was quite clear. It has nothing to do with being “macho” at all. I would have been quite prepared to drop back if that had been the best option.

The fact remains that accelerating out of trouble is sometimes the best option. It is, of course, a matter of judgement that depends on the circumstances at the time. In this regard, there is a brief account on Wikipedia of an incident that occurred in 1952 in which London Tower Bridge started to open while a double-decker bus was on it. The driver made a split-second decision to accelerate and jump the small gap that had already opened up. He accomplished this successfully and no one was seriously injured. Had he attempted to stop, one expects that the outcome might well have been tragic.



I’m afraid that there are those contributing to this thread who have a complete blind spot about the possible need, under some circumstances, to use acceleration as a means of avoiding an incident. The opinion seems to be that it is always possible to anticipate hazards with sufficient time to go through a well defined avoidance procedure. Anyone who needs to accelerate to avoid a problem is, therefore, demonstrating they are not competent in anticipating hazards. The possibility that sometimes they may not be amenable to anticipation seems not to be within their comprehension.



I suspect your comment about “those on this thread” refers to me. May I clarify my position, please.

We are all human and fallible, even the police driving instructors you refer to elsewhere. My point is that a competent driver should find him/herself in these “accelerate-out-of-danger” situations only on extremely rare occasions. So rare that it is a fairly weak argument against fitting speed limiters to vehicles.

It sounds as if Allan, above, was forced into this situation by other people’s collective irresponsible driving. I fully sympathise. The one occasion when “accelerate-out-of-danger” saved me was when I encountered three, bloody-minded HGV drivers at once – one blocking my safety gap to the left, one to the right and one close behind me – so accelerating was the only safe option.

So, yes, I agree absolutely, fully, entirely, wholly, completely, totally, 100% that “accelerate-out-of-danger” is sometimes the best and safest way to avoid an incident. But it should be rare and if you find it is happening frequently you really should be going back for a refresher advanced driving course run by the police.



I think a well known saying concerning the fit of caps is apposite!

The reason for my comment was your, not unexpected, response to Allan’s original post about his experience. You immediately assumed that it was all his fault that he was in the situation and that he could have avoided it by other means. As you say yourself from your own experience, though, acceleration is occasionally the only option as it was in this case.

My own situation is that in 60 years of motorcycling and car driving I have only had to employ the use of acceleration only on a couple of occasions, but on the one that I mentioned in my other post it saved me from serious injury or worse. The problem is not that one driver is in this situation on many occasions but rather that many drivers find themselves in the situation once when it is critical. This is why I would oppose the idea of automatic speed limiters. In another post I give some figures from 2001 which indicate that just 12.5% of accidents are attributed to excess speed. Note that excess speed does not merely mean exceeding the speed limit. It also has to be taken into account that a percentage of these incidents involve drivers operating illegally. So, at best, applying automatic speed limiters may have an effect on fewer than 12.5% of all accidents, but because of the resultant inability to accelerate out of danger, could introduce a whole new category of accidents.

On a lighter note, I saw an excellent example of nemesis following hubris this morning. A cyclist burst from a concealed entrance and crossed the road at high speed without any attempt to look first to see if it was safe to do so – he was obviously working on the principle adopted by many cyclists that it is the responsibility of others to avoid him. When he reached to far side of he road he attempted to jump the kerb but got it terribly wrong and both he and his cycle did a most impressive forward somersault. What happened afterwards I have no idea, the bus on which I was travelling moved on.



I strongly suspect that, under the surface, we’re pretty much in agreement.

I did not assume it was all Allan’s fault. I was partly ‘stirring things’ to make this thread a little more lively, and partly because, from his description, Allan had shown no justification for accelerating.

But I still maintain it isn’t a good argument for not fitting speed limiters. Limiters would almost certainly be set several mph higher than the speed limit and it would be simple to allow short bursts of even higher speeds (though I suspect the ‘boy-racers’ would abuse this!). Ultimately, we’re a democracy and can demand some adjustments to the basic principle of speed limiting.

Bear in mind, too, that many drivers do not have the option to “accelerate-out-of-danger” – their cars are simply not powerful enough.

As I say elsewhere, I’m against speed limiters. But not because of the “accelerate-out-of-danger” argument.

On a lighter, but loosely relevant note – many years ago I borrowed a car from the company car pool (a diesel Citroen). I pulled out to overtake a van and the engine simply ‘died’. About 10 seconds later it returned to normal. I was told later that to prevent engine damage it simply cut off the fuel supply for ten seconds at a preset engine speed. Terrifying!


” … from his description, Allan had shown no justification for accelerating.”

I prefer to work on the assumption that comments are being made by an intelligent person who has justification for his actions so do not usually need a whole essay of reasons to be provided. By the way, I thought this forum was for the civilised exchange of experiences and did not need to ‘stirred up to make them lively’.


spot on except for suggestion of a trial. It is a proposal with no merit.


Speed alone does not cause accidents. Bad driving is the root cause and that should be tackled rather than speed. One only has to compare manned traffic policing between the UK and elsewhere in Europe. Whereas in most European countries manned speed traps are very common, the British police prefer a more pragmatic approach by driving around looking for bad drivers. The French in particular have been targeting speed in recent years because of a high accident rate, but they neglect to tackle the root problem such as tailgating and handheld mobile phone use.


I agree that bad driving is the problem, but there is no doubt that speed affects the severity of accidents.

I wonder if use of cruise control is already contributing to tailgating and if automatic speed limiters might further increase this problem. It’s one of the reasons I’m keen on trials.

Mobile phones are my biggest concern, and I frequently see drivers distracted by phones. I am not convinced that hands-free phones are much better in this respect.


NFH, I’d agree that speed alone does not cause accidents. However, my attitude is that the faster you drive, the better your awareness of the road and drivers around you needs to be for it to be safe. In my mind, the most dangerous drivers on the roads are the ones with little awareness of the road around them. Bad drivers are dangerous at any speed and if bad drivers drive fast, everyone’s at risk!

Wavechange, I’d also agree that drivers using mobile phones are an issue too. I’d be interested to see trials of removing all road signs which force drivers to assess the road ahead of them rather than see a speed limit and drive at that speed whatever the conditions/road are like. Weirdly, I think that this could make roads safer as people would have to use their own judgement rather than blindly driving at the speed limit and paying little attention to what’s going on around them…


We’ve all seen the results of fitting speed limiters to HGV’s. 90kph and within a very short space of time the nearside lane of a motorway becomes clogged.The middle lane is’nt much better as who can blame a lorry driver for overtaking an HGV that is set at 88kph? Just imagine the pandemonium this would create? Would there be seperate limits for caravan drivers? And finally, are the Government really set on imposing road tolls on motorways, which as a result of speed regulation, will be no better than ‘A’ roads! I suppose the only shred of sunlight at the end of the tunnel is, a three lane motorway will become (in effect) three seperate motorways.



“my attitude is that the faster you drive, the better your awareness of the road ”

Perhaps. But I suspect the very slight increase in awareness is more than offset by other factors (e.g. how long you have to react to dangerous situations, increased stopping distances, etc).

Do you have access to any research that show higher speed = better awareness?


Gradivus – You’ve missed the key part of what I said! The faster people drive, the better their awareness NEEDS TO BE, for them to be safe.

I’m not condoning driving faster, but saying that awareness of the roads is more of an issue than absolute speed in my eyes. People can drive slowly and be dangerous if they don’t have decent awareness of what’s going on around them.



My apologies. I misread your post. Me culpa.

I fully agree with what you are saying.


@mike: Why should a lorry driver feel obliged to overtake an HGV set at 88kph? What we often see is one lorry in lane 2 overtaking another in lane 1 but at the same or marginally faster speed, making the manoeuvre pointless.

Speed limiters? Fantastic idea! If you don’t like the speed limits, campaign to change them. My only reservation is the accuracy of speed measuring. Of the past six cars I have owned, only one has had an accurate speedometer. The other five overestimated speed. Strange, because when hiring cars in the US they were always spot on. How do I know? By measuring at constant speed using GPS.

Now, given that GPS is inaccurate at variable speed and car speedometers are inaccurate generally in this country, what is the chance the speed limiters will all measure speed accurately before limiting it?


Would it reduce insurance premiums ? Probably not. Would it be free to install? Probably not. And as I already use my cars cruise control to limit my speed, I can’t see any benefit. Just an added cost. And I bet premiums will go up if you don’t get one fitted if it is rolled out.


@william: If it reduced the number and severity of accidents then, yes, it would reduce insurance premiums, as would a 20mph limit in built up areas and a curfew on young drivers.


I once had to swerve and increase speed to avoid hitting another car that just came speeding out of a side road into my path. I realised that I did not have time to stop and luckily avoided an accident. In an emergency situation you are unlikely to think about overriding the limiter, especially if you are unused to it.

I often break the speed limit on motorways to overtake middle lane hoggers travelling at below 70mph. If I was electronically limited to 70mph then I would be fast lane hogging or overtaking lane hogging or even middle lane hogging until I get the opportunity to move into the inside lane. Sometimes I have done it to get away from a wobbly driver who is on the hanheld mobile phone or looking at a book.

The EU should instead get car manufacturers to fit a device to warn us if we are exceeding the speed limit. Something like the Ryanair fanfare they play at the end of each flight to acclaim the fact that yet another Ryanair flight has arrived on time. I have fanfares, bells etc. on my Sat Nav but with road noise, radio or music playing and sometimes chatter I don’t really hear them. Also I only use the Sat Nav when I don’t know the route.

Perhaps a Dashcam and fanfares would improve our driving more than having speed limiters. Some drivers could do with distanceomoters to prevent them from tailgating. They obviously do not think about stopping in an emergency.

Patrick McLoughlin we want Dashcams that are permanent fixtures in our cars and loud fan fares that override our radio and music broadcasts as a speeding warning. This could be incorporated into the Dashcam. If we are then involved in an accident or are witnesses to an accident our Dashcam will be an unbiased witness. This may deter motorists from speeding and dangerous driving, especially if our insurance companies adjust premiums accordingly.


@Figgerty: “The EU should instead get car manufacturers to fit a device to warn us if we are exceeding the speed limit.”

It’s called a SatNav.


First you have to own a sat nav and then you must switch it on if you own one to receive a warning that you are exceeding the speed limit. I only switch on the sat nav when I’m unsure of a route. I would much rather listen to the radio in the car or even my passengers.


Speed limmiters have been mandertory on trucks and busses for quite some time. So why not for other vehicles?


Have you ever been stuck in very long queue of traffic whilst one slow moving lorry is being overtaken by another one travelling at 1 mph more? The overtaking manoeuvre can cover several miles.


Oh and I should add, I guess not all buses have them as I’ve seen several pulling away from me in a 30 limit when I’m doing 30.


How do you know you are doing 30mph? Most speedometers over-read depending on the wear on tyres. The more worn your tyres, the more your speedometer will over-read. For example, when my speedometer says I’m doing 120mph, a much more accurate GPS device shows that I’m doing only around 112mph.


I believe most speedometers register slightly higher speeds than the real speed due to legal concerns that drivers would blame the car manufacturer if they were charged for speeding and the speedometer did not register that they were driving above the speed limit. I haven’t heard claims that tyre wear would make a distance before…where have you seen this?


It is well known in the motor trade that tyre wear causes speedometers to over-read. It’s simple physics anyway. If the total radius of a wheel and tyre becomes smaller, then the wheel will need to do more revolutions to cover the same distance. Given that speedometers are based on wheel revolutions (as opposed to GPS for example), speedometers become inaccurate over time. In my experience, a BMW, Mercedes or Volvo with new fully inflated tyres shows the correct speed on its speedometer (compared to a GPS device). Many other manufacturers’ speedometers over-read even before any tyre wear.

It’s very annoying when I’m behind someone who slams on the brakes before a speed camera when they’re already at the speed limit but their speedometer misleads them into thinking they were over the speed limit.


I just assume that people will slam on the brakes when approaching a speed camera, and sometimes pass it at 20 mph below the speed limit. What annoys me is when people overtake because I have left sensible gap behind the car in front to help cope with inconsiderate drivers.


NFH, I understand the logic of tyre wear affecting speedometer readings, however I’d expect the difference between new and worn tyres to be negligible. Having briefly looked into it, I believe the variation in diameter between supposedly identically sized tyres would make more of a difference than wear. Likewise I would expect tyre pressures to play a big part too…

Ultimately it would make sense if car manufacturers made speedometers show the most accurate speed possible so that a driver with average-diameter-for-their-size tyres inflated to the correct pressure would have an accurate reading.

As for people slamming their brakes on before speed cameras, many people do that whether they’re driving above or below the speed limit – ideally people would notice speed cameras early on and make sure they’re driving at a suitable speed well before the camera which would keep traffic flowing better and avoid some accidents where people brake unnecessarily hard for cameras.


I live near a speed camera and the majority of drivers don’t slam their brakes on at the last minute; they all know it’s there and start braking well in advance. Mind you I did see one guy brake for camera and still get flashed.

The difference in diameter cause by tyre wear makes very little difference to speedometer reading. Likewise tyre pressure unless the tyre is seriously under inflated.

As far as speed limiters are concerned I think it’s inevitable although there may be problems retro-fitting them to all existing cars.


As far as I know, the law says that speedometers must never understate your speed and cannot overstate it by more than 10% + 3mph.

I’m not absolutely certain about the mathematics, but GPS units in open countryside and at motorway speeds will be somewhat more accurate than speedometers.

In my own experience, BMW speedometers are fairly accurate, Toyota’s overestimate by about 10%. So, if you drive at an indicated 70mph on a 200 mile journey, you’ll get there 20 minutes sooner in a BMW!


Where do you get this information from about the speedometers on BMWs and Toyotas?


As he says, it’s in his own experience. Sometimes as a passenger in a car, I open a GPS app on my phone and see whether the speedometer is accurate. BMW do seem to be accurate, as are Mercedes and Volvo. Presumably Gradivus has done something similar.


Tyre wear has negligible effect on speedometer readings.

Take the example of a fairly standard tyre of 600mm diameter (just over 1.8 metres circumference). The typical tread wear allowance is 6mm. That reduces the diameter by 12mm at end of life. 12/600 x 100% = 2%. So for any legal speed, the effect of tread wear is to cause a reduction of around 0.6 – 1.4 mph.

Anyway, in terms of a defence, it might not be too clever to point out that your speeding was as a result of your making allowances for running on badly worn tyres.


Another way to verify the accuracy of your speedometer is to use the Type 1 Motorway Marker Posts, set at intervals of 100 metres. Easy, since 1.6 Kilometres – the distance between 17 marker posts – is almost exactly 1 mile. On a clear Motorway, drive at exactly 60 mph according to your speedometer (use cruise control if you have it) and get a passenger to time the distance. After that it is simple maths to calculate your measured speed.


Hi Em,
0.6-1.4mph inaccuracy from tyre wear might seem negligible by itself, however the cumulative impact of tyre wear, speedometer inaccuracy and the varying diameter of supposedly identical tyres could be much more than that.

I’ve had a quick look at the difference in circumference of several 18 inch tyres (225/40/18 tyre size) which was up to 7%, and I believe that could account for a further 4mph difference at 60mph. Add that to say, 1mph for tyre wear and several mph for speedometer inaccuracy that could on paper account for a 7mph difference at 60mph. Obviously there are tolerances in all of these factors, but certain combinations of inaccurate speedometers, tyres and tyre wear could account for significantly inaccurate speedometer readings.


Christofer wrote: ‘Ultimately it would make sense if car manufacturers made speedometers show the most accurate speed possible so that a driver with average-diameter-for-their-size tyres inflated to the correct pressure would have an accurate reading.’

The danger of improving accuracy is keeping within the requirement that the speedometer never indicates a lower speed than the true speed. Perhaps the new technology will deliver reliable accurate speed measurement, but until this has been demonstrated, I am not concerned with the status quo.

It would be good to have accurate fuel gauges too. I can usually manage 100 miles before mine starts to move from the full mark, and I recently managed 140 miles.


I believe the technology to measure speed very accurately already exists. In fact, you are holding it in your hand right now: the optical mouse. You just need a lens under the front bumper, shining a light on the road, and a wash/wipe system to get rid of mud and keep the lens clean. And use the old mechanism as a backup that a computer automatically switches to in case it loses the signal from the lens. I wonder if this has been patented yet.

By the way, a question for Christofer Lloyd – you said there’s a variation of up to 7% in tyre sizes for tyres of the same nominal size. Have you seen any claims of improved economy made by manufacturers whose tyres are smaller? A 7% tyre diameter reduction would cause a 7% speed reduction if the driver keeps the same speedo reading, and this would cause a 14% reduction in fuel consumption (since at high speeds fuel consumption is roughly proportional to the square of the speed.) When you road-test the tyres, do you use a separate, accurate speedometer that shows true speed, or do you rely on the car’s speedo?


@L2: I can support that about Toyotas after driving three Rav-4s but our current Yaris (3 years old) is spot on.


Maybe. It depends on how well the technology is implemented.

If it is a simple governor that would never allow a vehicle to exceed the limit by even 1mph, then no. Whilst I certainly don’t subscribe to that hoary old chestnut about needing to accelerate out of danger, let’s be honest and admit we all make the occasional mistake about when it is safe to overtake, or the vehicle being overtaken proves to be obstinate and speeds up without warning. An extra burst of speed can sometimes be a better and less risky option than applying the brakes, especially when you are trapped in the outside lane on an otherwise clear motorway. I don’t need some device that is even dumber than me or the other driver, automatically applying the brakes without any intelligence of the situation what-so-ever!

Modern computer technologies should be able to come up with something much more sophisticated. It might be sufficient to track the vehicle’s average speed against the limit and allow a vehicle to build up a small buffer for safer overtaking if under the speed limit and maybe apply a financial penalty if persistently over the limit.

So, for instance, a vehicle following a tractor at 20mph in a 30 mph zone would build up an overtaking allowance, permitting it – technically if not legally – to accelerate beyond 30 mph for a few seconds, but still capped at maybe 40 mph. This is more than sufficient to overtake in a few seconds if things start to get really awkward.

After a few more seconds of driving in excess of the stated limit, the vehicle would be slowed down to that limit and no further allowance would remain. Thus a vehicle following another vehicle already travelling at the legal limit would never build up an allowance sufficient to even attempt to overtake it.

Another condition is that highway authorities would have to lighten up on some of the ridiculous speed limits now in force. These seem to be set on the basis that it is deemed safe to drive at up to x mph, but they set the limit at (x-10) mph, as no one is going to obey it anyway. And of course all speed humps, annoying “Slow Down” signs that flash at you when travelling at under the legal limit and other traffic calming measures would have to be removed immediately.


It’s not a ‘hoary old chestnut’ about needing to accelerate out of danger. Such acceleration saved be from serious injury, or worse, when a lorry towing a trailer started to pull out as I was overtaking it on the M5 in the days when it was a two lane motorway. Staying at the speed I was travelling or braking would have resulted in being pushed into the central crash barrier by the lorry or by the trailer. Fortunately I had a car with sufficient acceleration to get me clear which is why I am still around to write this!

Some years ago I attended an advanced driving course run by the police. It was made clear by the instructors that acceleration is a significant means of avoiding accidents and drivers should always drive in the gear most appropriate to achieve this.

I would not be in favour of anyone or anything not having an awareness of the precise traffic conditions in which I found myself taking control of any aspect of my car. Technology is not infallible and the consequences of a malfunction – such as the incorrect detection of a speed limit – causing brakes to be applied in error could be major.


>>> Some years ago I attended an advanced driving course run by the police. It was made clear by the instructors that acceleration is a significant means of avoiding accidents and drivers should always drive in the gear most appropriate to achieve this. <<<

Correct. It's the LAST stage of a FIVE phase approach to dealing with hazards:


Before ACCELERATION you adjust your SPEED appropriate to the hazard being approached.

If you took the hazard at 70mph, then you left yourself no where to go when you needed to accelerate out of danger.

As I said in my post, we all make mistakes and any system of speed limitation should take account of that. But accept that the legal speed limit is not a target to aim for and if you choose to drive at that speed you then reduce your margin for error.



I think you and tonyp are mis-interpreting the Roadcraft system/manual.

SPEED – refers to REDUCING your speed, from your current safe and legal speed, to the speed appropriate for the hazard. (So taking a hazard at 70mph is a rather curious concept)

Gear – having SLOWED to the appropriate speed you select the appropriate gear for that speed.

ACCELERATION – having successfully CLEARED the hazard, you accelerate back to a safe and legal speed.

It’s a long time since I read Roadcraft, but I cannot recall any statements of when it is acceptable to exceed the speed limit.

Or any police driving instructor prepared to go publicly on record and say that speeding is OK if, for example, you want to overtake.


I suspect that both Em and gravidus have failed in a rather comprehensive manner to understand the import of my previous posting.

>If you took the hazard at 70mph, then you left yourself no where to go when you needed to accelerate out of danger.Or any police driving instructor prepared to go publicly on record and say that speeding is OK if, for example, you want to overtake.<

If you had read and understood what I said, there was no reference to exceeding speed limits just that, under some circumstances, acceleration may be the only way to avoid being involved in an accident. It was certainly implicit that if this meant a transient period over the limit then so be it. There was no implication in my post that the instructor said that it was OK to exceed speed limits simply to carry out a normal overtaking manoeuvre.


I’m not sure what happened to the last post – a lot of text simply disappeared! Let’s try again.

I suspect that both Em and gravidus have failed in a rather comprehensive manner to understand the import of my previous posting.

>>If you took the hazard at 70mph, then you left yourself no where to go when you needed to accelerate out of danger.<>Or any police driving instructor prepared to go publicly on record and say that speeding is OK if, for example, you want to overtake.<<

If you had read and understood what I said, there was no reference to exceeding speed limits just that, under some unanticipated circumstances, acceleration may be the only way to avoid being involved in an accident. It was certainly implicit that if this meant a transient period over the limit then so be it. There was no implication in my post that the instructor said that it was OK to exceed speed limits simply to carry out a normal overtaking manoeuvre.


This is very strange, the same thing has happened again. Perhaps it’s the use of greater than and less than symbols to indicate quotation. So I’ll try yet again with a different approach.

I suspect that both Em and gravidus have failed in a rather comprehensive manner to understand the import of my previous posting.

“If you took the hazard at 70mph, then you left yourself no where to go when you needed to accelerate out of danger.”

This is a rather strange comment. Just what speed would you say is appropriate when overtaking a lorry travelling at 60mph on the motorway? 61mph? 62mph? Or what? Or are you saying that overtaking a lorry on the motorway is such a horrendous hazard that it should not be attempted? In fact my speed was actually irrelevant, other than the obvious need for it to be higher than that of the vehicle being overtaken, because it would have been fairly catastrophic to be crushed against the central crash barrier by a lorry plus trailer travelling at 60mph even if I was stationary at the time.

The comment about acceleration being the last step in a five stage process is utterly irrelevant. The instructor was not talking about regaining speed after negotiating a hazard but in its use in some circumstances not amenable to anticipation. I accept that I am a normal fallible human being and by no means perfect, and drive accordingly. It does worry me when people seem to imply that they are infallible and are able to anticipate all eventualities – it often means that they are not aware of a lot going on around them! Perhaps a little more humility and a little less preaching would be a good idea.

“Or any police driving instructor prepared to go publicly on record and say that speeding is OK if, for example, you want to overtake.”

If you had read and understood what I said, there was no reference to exceeding speed limits just that, under some circumstances, acceleration may be the only way to avoid being involved in an accident. It was certainly implicit that if this meant a transient period over the limit then so be it. There was no implication in my post that the instructor said that it was OK to exceed speed limits simply to carry out a normal overtaking manoeuvre.


Hi Tonyg, yes your use of greater than and less than is what we use for coding on the site. This is stripping out some of the copy. Sorry about that.


Thanks for that information Patrick, now I know! It just shows that one is never too old to learn new tricks


Odd that Transport Secretary Patrick McLoughlin thinks it is now OK that 1 in 300 of Britain’s road users is injured every year in road traffic accidents. Which third world’s Banana Republic transport system does he think he’s in charge of?

Never mind Big Brother – it shows up government’s disgraceful complacency for the welfare of citizens going about their daily business through its failure to provide safe and effective systems of transport.


Hi Em. I’d be interested to hear how you would put more importance on the welfare of citizens. Any form of transport has inherent dangers and there are many dangers even within our own homes. We could have draconian very low speed limits, but that would dramatically increase journey times and still not make transport completely safe. Also I wonder what effective systems of transport would you like the government to provide? People’s safety is definitely very important, but transport is also very important for the running of our country and I’m not sure that we can make transport completely safe with current technology…


Em has a point. In 2012 1,745 people died on British roads but the Transport Minister regards that as something to be proud of because it’s the lowest rate in Europe! If one tenth that number died every year on the railways or in commercial aviation over the UK there would be public enquiries, questions in the house, resignations and the system shut down entirely.


Yes, that is a lot of people to die on the roads. However, I don’t believe you’re comparing like for like.

Cars are driven by a huge proportion of the population who may have passed a basic driving test many decades ago and drive on a dense network of roads packed with other vehicles and pedestrians. Trains and planes are operated by professionals who are specifically trained to pilot these machines for a living. And the format of train tracks/flying means that crashing into other vehicles/pedestrians is much much less likely. Short of a technical fault or extreme human error, crashes are very unlikely.

How do you propose reducing deaths on the road Phil?


Well you’ve partially answered your own question; better, more rigorous and continuous driver training would help but you ask as if there’s nothing that can be done and overall your attitude appears to be that the situation is acceptable. Is that the official Which? position?


Hi Christofer – You set out the agenda for this Convo and, as I understand it, it is not about having: “draconian very low speed limits”. It’s about the potential to use a technology to help to enforce the law as it is, right or wrong.

Unfortunately, politicians have a very poor track record of introducing changes that may be unpopular with a vocal minority of the population. Look back to how long it took Parliament to introduce laws requiring the wearing of seatbelts in cars (10 years) and crash helmets by motorcyclists. People continued to die whilst lobbyists and MPs of low intelligence argued against these simplest of safety measures on grounds of personal liberty and fluke circumstance.

“Transport is also very important for the running of our country”. I agree, but this isn’t the Wild West. The lives and safety of citizens should not be put at risk by less responsible companies who are happy or even encourage their employees to break transportation laws to make more profit. Or Ministers who can’t be bothered to regulate their laws and investigate the potential of further safety improvements. I thought the days when citizens could be sacrificed for the greater good of Britain plc had passed.

What would I do?

The key to improving transport safety is separation of traffic, as you have pointed out below with respect to trains and planes. Pedestrians should not be forced to share roads with cars and lorries, nor cyclists. This is possible, even in cities like London. There is no reason why every street has to be a thoroughfare for motorised vehicles.

Where separation is simply not possible, speed limits need to be low enough to ensure there is some parity between the different classes of road user. Speed limits are of no use at protecting vulnerable road users if they are only enforced retrospectively through a system of penalties for infringement.

It needs money and vision to achieve all this, so speed becomes less of a factor in the seriousness of the road accidents that are inevitable. More than enough money is generated by the taxation of existing transport systems to pay for major improvements that would offer both economic and social benefits, including a reduction in the cost to the NHS of treating RTA victims. As a country, we seem to lack the vision and will to do anything about it, but it’s certainly not OK as it is.

And where does Which? stand on all this? We’re getting very mixed messages from your personal postings about the need for any reform.


I agree with your points, Em, particularly about segregation of different users and that there is scope to exclude motor vehicles for more roads. However, this discussion focuses on devices to inform of speed limits or to control maximum speed of vehicles.

My view is that providing drivers with visual and/or audible warning that they reach and exceed the speed limit in force would do more good than harm. Obviously control of maximum speed is more controversial.


Hi Phil,
Yes, I personally would be very happy to see more rigorous, continued driver training, though I accept this is neither practical nor cheap. No, this is not the official Which? position – I’m playing devil’s advocate to encourage debate by offering another interpretation.

And no, on a personal level I don’t find the current levels of road deaths acceptable or unavoidable – my point was that I also don’t think it’s that plausible to expect no deaths on the road either, especially when there is a dense, heavily used road system, with cars, buses, lorries, bikes and pedestrians all vying for space. There is of course significant room for improvement and lowering the death toll…


Hi Em,
As I said to Phil, I am not presenting the official Which? position – I’m playing devil’s advocate to encourage debate by offering another interpretation.

Yes, the article is about the potential introduction of speed limiters. My comment about draconian speed limits refers to both speed limits and speed limiters and the perception that absolute speed is the sole issue that needs to be addressed, which in my eyes is only part of the problem. As you’ve mentioned, improved road design could also make a big impact, as could greater driver awareness of the roads around them.

Additionally, if speed limiters were introduced, an intelligent system, such as a sophisticated limiter with a buffer allowance as you described, could be a much more workable system than one than a simple limiter which restricts the car to the exact limit full stop.

Separation of traffic makes a lot of sense, though I’m not sure how possible that is in cities like London, which have high traffic levels and limited space. My gut feeling is that this would require a huge amount of expenditure to restructure the city’s roads, though I’m sure it could result in improvements in safety in those areas.

I can see the logic in lowering speed limits to ensure parity across different types of road user too, but I wonder how low speed limits would have to be to do that – would it have to be calibrated for the slowest cyclist? Suffice it to say, I don’t envy the job of road designers to tick the many safety, practicality and traffic flow boxes!


Amazing to get this far into a Conversation without any attempt to analyse the casualty figures to see what amount of the incidents are actually speed related. We also have a Conversation started with a reference to road deaths in the EU with no figures for the UK. Helpful.

In 2012 the rate was 1754 killed. Of those it may be interesting to know how many were car drivers/ passengers and how many were pedestrians and cyclists. the information is in here:

If we accept that there is a law of diminishing returns in amount of money spent to reduction in numbers that would be sensible. My belief is that the quickest return for money spent will be to isolate where needed and encourage cycling priority in other areas. The increase in cycling deaths is very counter-productive if the nation is encouraging a healthy life style.

I understand at Leiden station they have spaces for 13,000 bicycles and as for the fatality rates:


“Speed related” is a very ambiguous term. You could argue that all collisions are a result of not being able to stop in time (eg. people driving too fast to start with), or blame other causes for many of these, such as a lack of awareness. And it is also important to balance the importance of safety and journey times – both are important for the country to run smoothly.

I don’t understand your comments regarding the increase in cycling deaths being “counter-productive”. This is a statistic – it’s not being propagated to dissuade people from cycling. The logic of cycling more makes sense, however the reason many journeys are taken by car is due to longer journeys and other issues such as carrying luggage etc. A complete cycling priority in my eyes would be counter productive too.


It’s been a while since I was in Holland but my recollection is that Dutch cyclists tend to obey the law and not run red lights, ignore pedestrian crossings etc like some morons in this country. That might go someway to explaining their greater longevity.


Rather than saying “speed related”, I would be interested in the statistics showing what percentage of accidents involved speeds in excess of the legal limit. This would be directly relevant to the topic of the conversation: speed limiters would limit your speed to the legal limit, which is just an arbitrary number, and not necessarily the appropriate speed for the conditions. (By “arbitrary number” I don’t mean a number taken at random, but that speeds are chosen to be exact multiples of 10 mph which is quite arbitrary, and also usually don’t vary according to weather and traffic conditions.)

Dual display says:
6 September 2013

Do I want more “big brother”? No. Do I think that it make any significant impact on road deaths? No.
BUT perhaps there is a way in which the underlying concept would help.
My SatNav displays both my current speed and what it thinks the local speed limit is, but with all the changes that local authorities make to speed limits the SatNav is not always up to date.
SO … why can’t we have all cars fitted with a dual speed display. One side is your actual GPS calibrated speed. The other is the correct local speed limit. The background colour of your actual speed would change from a neutral colour to orange and then to red if you exceeded the limit.


Before fitting limiters to cars, it would be nice if whoever is responsible made road signs more visible by cutting down all the overgrown bushes that obscure them. I’d also like to see more speed limits painted on roads.


Why not do both?

In fact, there is no need for physical signs, GPS or complex visual recognition systems to determine the current speed limit. As I pointed out in another Convo, all information can be buried in the road surface or attached to existing signs in the form of cheap electronic tags or bar codes.

Why even a high-end smart phone has the technology to read these things, so why not a motor vehicle? A simple in-car display could then pick up speed limits and warnings. No excuses then … .


We can discuss for ever the need for improvements in road safety. The, rather insoluble, problem is that whatever we do depends on the fact that fallible human beings are a major part of the equation. Any honest driver/cyclist/pedestrian will admit that they have made mistakes which could have had serious consequences but, thanks to fortuitous circumstances, they managed to avoid them. Whatever systems are put into place to make things safer also depend on these fallible human beings so are equally capable of going wrong. To believe that there is a ‘magic bullet’ capable of making a dramatic improvement in road casualties is wishful thinking. All we can hope for is a series of incremental improvements.

There is one area, though, which could have a significant effect. These days I spend more time as a pedestrian than as a driver so tend to be more aware of the activities of those using the road. One conclusion that I have reached is that the rate of accidents to cyclists is as low as it is as a consequence of the competence of other road users! Many seem to consider that they are somehow immortal and that it is the responsibility of everyone else to avoid them, they often carry out manoeuvres that make my hair stand on end just to watch. I do feel that there is a good case for mandatory cycling proficiency tests with especial attention being paid to the need to obey the rules of the road.

As a cyclist and motorcyclist many years ago I was taught the three golden rules of safety:

– Never become the meat in a sandwich – avoid being between two solid object if one or both of them are likely to move.

– Never sit in the blind spot of a vehicle – if you can’t see the driver, the driver can’t see you.

– Don’t expect the laws of physics to be changed for your benefit – vehicles need distance to stop and cannot turn instantaneously.

It is evident that many cyclists do not understand these ‘rules’, especially the second one. A particular problem is the number of cyclist who insist on charging up the inside of vehicles which are indicating that they are turning left, ignoring that fact that for much of this manoeuvre they are not visible to the driver.


To get back to the original question…

I’m against fitting speed limiters in cars.

Speed is, without any shadow of doubt, a very important factor in road safety. But the speed limit system is crude.

For example – What speed should you be doing when driving past a school: at school closing time (when the light is fading), on the last day of the winter term (when the kids are really keen to get home), in the first snow of the year (when the kids are excited, and your grip is diminished), in a cold car (with the windows liable to steam up) that you’ve just collected from a hire company (when you’re not-too-confident about the controls, etc), on your way home from work (when you’re feeling a little tired)?

Conversely, what speed could you safely do past that school at 5am on a bright, sunny late-July morning?

Accuracy of your speedometer is a red herring.
Accelerating out of trouble is a red herring (a competent driver reading the road correctly will find him/herself in such situations only extremely rarely).
Visibility of road signs is a red herring.
Being told what the speed limit is is a red herring.
And, fitting speed limiters to vehicles is a red herring.

What is NOT a red herring is better driving standards. Whether this be through better driver training, tougher driving tests, repeated driving tests or banning bad drivers, is open to debate.


A few years ago ‘The Times’published a letter which detailed a compilation of data from 13 police forces relating to the causes of accidents in 2001.

Inattention 25.8%

Failure to judge the other person’s path or speed 22.6%

Looked but did not see 19.7%

Behaviour, whether careless/thoughtless/reckless 18.4%

Failed to look 16.3%

Lack of judgement of own path 13.7%

Excessive speed 12.5%

Those of you of an arithmetic nature will have noticed that these figures add up to more than 100%. This is because some accidents are considered to involve more than one of the categories. What does surprise me is that there is no mention of drink-driving or mobile ‘phone useage. Perhaps the figures relating to these have simply been absorbed into the appropriate classifiations. Similarly, there is no indication of the pecentage of accidents caused by drivers operating illegally – ie disqualified, no insurance/road tax/MOT etc. No doubt the figures have changed in the meantime and, probably, a few new categories added. The figures from 2001 do, though, put things into perspective.

What does come out of these figures is that concentration on one factor alone, such as speed, is very unlikely to make any significant inroads into the overall accident rate. It has to be said, however, that speed is a significant factor in the severity of accidents. Speaking as a pedestrian, though, I’d rather be missed by an attentive driver travelling at 40mph than hit by an inattentive one at 30mph!



Speaking as a parent – even better to be missed by an attentive driver doing 20mph.

Especially since children have been known to run out into the road without warning, giving drivers little chance of avoiding an accident.

And I really, really must avoid mentioning “accelerating out of danger” here.

Seriously, I do agree wholeheartedly that speed is only one factor, and better standards of driving is probably a bigger factor



“Speaking as a parent – even better to be missed by an attentive driver doing 20mph.”

Personally, as long as they miss me I don’t really mind what speed they are going! I do accept, though, that excessive speed does not merely mean exceeding the speed limit and I do usually back off when I see children.

“And I really, really must avoid mentioning “accelerating out of danger” here.”

But you didn’t avoid it! Out of interest, what approach would you have taken in the situation that I described?

“Seriously, I do agree wholeheartedly that speed is only one factor, and better standards of driving is probably a bigger factor”

Better standards of driving are certainly a major factor in improving the accident rate but I often wonder how many of the ‘driver fault’ problems actually have a source outside the vehicle. For instance, how many cases are there of drivers being distracted by such things as the plethora of road signs that infest our road system?

Some years ago I was a member of an air transport safety committee. We were involved on one occasion in studying the high accident rate of helicopters servicing the North Sea oil rigs. Our remit was to identify problems and look at the possibilities of introducing systems to overcome them. A separate study was carried out by a psychologist to look at the way that pilots coped with the workload. This latter study came up with the interesting conclusion that pilots could cope at any one time with a maximum of three significant factors needing decisions. Any more than this and the probability of an erroneous decision increased quite significantly. Now helicopter pilots in particular must be amongst the most highly trained and competent people around so if they have problems with multiple significant events, what hope is there for the average motorist?


Speed limiters – no, there may be times when you need to exercise your judgement and not find your car responding as you wanted – dangerous.
Speed warning – I’d be all in favour of this being fitted in-car – satnav technology should provide this – anyone know how accurately (I haven’t trawled through the rest of the conversation to see). I admit to occasionally having been distracted and crept above the speed limit inadvertently and a warning would be appreciated.
I also like the radar speed indicator signs – I take notice of them, but it is surprising how many don’t – just like those who ignore speed limits anyway.
Driverless cars? Perish the thought.



GPS/SatNavs out on the open road report speed fairly accurately. The maths is quite complex, but in the real world we can look upon them as completely accurate for driving purposes.

Some SatNavs will warn you if you go over the speed limit. The problem is that if you try to stick to 70mph on a motorway your speed will inevitably wander between 68-ish and 72-ish. My SatNav goes “bong” each time speed goes from 70 to 71. After a few miles it’s so annoying that you’re faced with the choice of switching it off or throwing it out of the window.

Obviously there are potential solutions to this, but SatNav designers seem to have very limited imaginations!


GPS has insufficient integrity for it to be considered for anything of a critical nature – at least for land-based applications. What is making the situation worse is the availability of GPS jamming devices. These are often purchased by those whose vehicles are monitored so that confusing information on position is provided to those doing the monitoring. These devices can have quite large effective ranges – 50m radius has been quoted for some of the worst ones. It is surprising just how little power is required to jam GPS, just a few mW if it is on the correct frequency. A new breed of GPS interfering devices are starting to appear, These don’t simply block the signals from the satellites but ‘bend’ the information so that an incorrect position is reported rather than just a loss of ability to calculate position. Currently these are not, at least as far as I am aware, readily available but the time will come … !


Bad news for the future of driverless cars perhaps?


The whole idea of driverless cars fills me with dread! Having spent the whole of my career on R&D relating to safety-critical avionic systems and thereby understanding the difficulties of achieving high integrity, the thought of relying on critical systems designed on a minimum cost basis is not at all appealing!

It has to be said, though, that the driverless systems currently being developed use a combination of sensors so inaccuracy in one of them is not so much of a problem. The sat-nav in my car works on a similar basis. Normally it locks onto GPS but if this fails it falls back to dead reckoning based on car speed and steering movement – it works very well, even in such places as well screened underground car parks.

Caitlin says:
16 September 2013

Cars in the Emirates have a chime activated when going over the national speed limit. At times it was irritating, though it made a lot of sense.


Some vehicles in the UK have that system fitted and it’s definitely irritating. Here we call them ice cream vans.


Well the simple and quick answer is no.
Society and especially the EU seems hell bent on dumbing everything down to protect us all from ourselves to a level where before you know it we’re all basically automatons.

We’re already told how to think and speak, mustn’t say anything that might offend anyone or prosecution will result.
We’re already told what we should eat or how much we should drink, get sick after “self abuse” and you might not get the NHS treatment you’ve paid for.
We’re already frightened to be associated with anything even mildly adventurous for fear of litigation.
And I’m sure as time goes on more of this will come.

I’m more for majoring on personal responsibility. That is think for yourself and be aware of the consequences of doing anything stupid, like for example driving like a complete idiot.

I don’t really think it’s possible to protect people from themselves anyway because many don’t like being controlled and will simply rebel.
But you can reason, advise and educate, and if done well, and if given in an un-exaggerated right context way, the result will I believe be more effective than “attempts at control”.


I was recently on an Express Bus and was amazed to see that the driver ignored all speed limits except those which had average cameras on them. At one stage he turned off the taco graph in order to increase speed on a down slope. He seemed to know which kerbside cameras were functioning and which were not. I have followed many lorries at sixty-five to seventy miles per hour on the motorway and, similarly, very few seem to obey their forty miles an hour speed limit on ordinary roads. Those that do accumulate huge queues behind them.
With regard to in-built speed restrictors, I am amenable to being informed (and need to know) the maximum speeds for any road and my own speed in relation to those. This shouldn’t overload with bings, bongs and voice overs and it shouldn’t distract in heavy traffic either. But… It’s my car, I’m driving it, I’m in charge and responsible for what I do in it. There should be nothing that removes this responsibility and nothing that interferes with the car and my control of it.

Graeme says:
10 September 2014

It’s a great idea. I’m busy trying to find a GPS speed limiter for my car. I won’t have to worry about camera vans and it will save me fuel. They should be fitted to all new vehicles.

John says:
6 May 2015

It strikes me that a system that controlled the speed but that allowed the driver a few seconds of ‘override’ would satisfy most situations. If a driver persistently used the override it might be reasonable for the software to restrict its use (and warn the driver).

My experience of driving over the years is that speed limits are obeyed by a greater percentage of driver now than before speed cameras became ubiquitous. However, I’ve become fed up of being frightened by drivers who clearly believe that they are immortal and that normal rules do not apply to them. These people need to be controlled. My local councils response seems to be to put in ‘traffic calming measures’, these have the opposite effect on most people who get annoyed, are treated as a kind of adventure park by speeders and are unnoticed by drivers of big 4x4s. They (the humps, etc.) cause drivers to concentrate on missing the obstacles and not on missing pedestrians, cyclists and make me hope I never need an ambulance in an emergency.

There is no clear evidence that humps reduce accidents, only that they reduce average speeds. Speed limiters of the type under discussion would do that without the payload of noise, discomfort and pollution produced by humps, and I commend then to the group!


The Uk Gov won’t introduce this, not because it’s EU interference but because of the huge amount of income they make from fines – were we automatically restricted to the speed limits they would loose possibly millions in income as a result.