Limiting Speed, Limiting Safety

How the totalitarian threat of external vehicle control threatens a road safety disaster

Effect on Driving Style
Safety Implications
The Cruise Control Menace
Effect on Vehicle Design
Implications for Motoryclists
The Speed Limit Regime
How the Changeover Would be Achieved
Other Considerations


The technology now exists, through a combination of electronic engine control, and the Global Positioning System (GPS) to control motor vehicles automatically to ensure they do not exceed posted speed limits. This system is referred to as External Vehicle Speed Control (EVSC). Many campaigners for "road safety" have welcomed this as a way to greatly reduce the toll of death and injury on the roads, much of which is often attributed to excess speed. Why should drivers be given the "freedom" to do something that is illegal anyway? But, in reality, EVSC would lead to a dramatically different atmosphere on the roads and it is questionable whether it would deliver any worthwhile safety benefits.

Effect on Driving Style

Inevitably limiters will lead to people approaching their driving in a different way. Currently, drivers will be constantly adjusting their speed to take account of the different road conditions and hazards they encounter. If they didn't learn to do that as second nature they would crash all the time. However, on most roads, particularly 30-limit urban main roads and 70-limit motorways, traffic tends to travel above the speed limit in free-flowing conditions. The implication is that, rather than the limiter being something that would give drivers an occasional nudge when they went too fast, they would be driving "on the limiter" most of the time, which is an artificial driving style. Vehicles would travel along in cohorts all at exactly the same, limited speed. Faster progress would only be possible by out-accelerating and out-braking other vehicles at the points where speed limits change, so these could tend to become "accident blackspots". It is also probable that the changeovers between speed limit areas would need to be more graduated to prevent problems occurring.

Limiters would make safe overtaking much more difficult, except of very slow vehicles, and would lead to much greater intolerance of drivers who were unable to maintain the limited speed, particularly on single-carriageway rural roads. It is easy to foresee much more aggressive tailgating and even bumping of slow vehicles in queues becoming commonplace. Limiters would also encourage bunching of cars on motorways, in much the same way as we currently see with trucks limited to 90 kph. You would be travelling behind the same vehicle for mile after mile, making motorway driving even more boring than it often is at present.

Safety Implications

Any speed limit is at best only a very arbitrary approximation to the maximum safe speed at which it is possible to travel. Depending on the circumstances, it may be entirely safe to travel above the posted speed limit, in particular since many speed limits have been cut by local authorities for reasons unrelated to road safety, with the express intent of delaying and frustrating drivers. Equally, though, in plenty of situations it is not safe to travel at or just below the limit. Drivers have to set their speed at an appropriate level for the conditions. If that responsibility is taken away from them then they are likely to gain a false sense of self-confidence and act less responsibly in other respects.

The proportion of road accidents caused by excessive speed over the posted limit is a subject of controversy, but in-depth analysis of research such as Transport Research Laboratory Report TRL323 suggests it accounts for less than 5% of accidents, and may be an exacerbating factor, although not a direct cause, in another 5%. So 90% of accidents are totally unrelated to speeding above the posted limit, and EVSC will do nothing to stop them. Indeed, common sense suggests that the key factor in accidents is poor observation, risk assessment and hazard perception, particularly when negotiating junctions where there are conflicting traffic movements. EVSC completely fails to address this, and is very likely to make matters worse by encouraging drivers - as explained above - to take less responsibility for their actions.

It is very dangerous to imply that it is always safe to drive at the posted speed limit, yet EVSC will encourage drivers in this belief, so we are likely to see them ploughing on regardless at the maximum limited speed when the conditions dictate that they should slow down. This has indeed been proved by research showing that drivers with limiters are much more reluctant to slow down in dangerous conditions, such as in fog on the motorway.

There is also a strong likelihood that limiters would lead to an increase in single-vehicle accidents on rural bends as drivers tried to keep their speed up while going through them.

The Cruise Control Menace

There is also the vexed question of cruise control. This is a system which allows the vehicle to maintain a steady speed without the driver using either the accelerator or the brakes, using essentially the same technology as a variable speed limiter. Traditionally only found on luxury cars, it is now becoming available on many vehicles lower down the price range. Used properly, it can be a boon for long-distance cruising on the motorway, but if you're not careful it can be dangerous as you have to make a positive decision to override the system to reduce speed, rather than just lifting off the gas a bit.

It's easy to imagine under a regime of speed limiters that cruise control would become general on cars, and drivers would simply set the cruise to "max" and drive around at the maximum permitted speed wherever possible. Of course, this can be achieved by driving "pedal to the metal" everywhere, but if cruise control is engaged it will make the potential consequences even more serious, as the driver will simply be able to relax. There could be a need to fit cars with a "dead man's handle" as found on trains, to cut off the power if the driver fails to respond.

I have also seen suggestions that the EVSC system would not allow driving right on the limit, but instead would progressively cut off the power if the driver tried to exceed it. Rather than seesawing down the road, drivers would need to achieve a difficult balancing act of driving as near to the limit as possible without exceeding it, which inevitably would breed much resentment and annoyance.

Effect on Vehicle Design

All new cars currently sold in the UK can exceed the 70 mph motorway speed limit, virtually all by at least 20 mph. Average family saloons such as a 1.8 Mondeo can exceed 120 mph. Unless you regularly drive on derestricted German autobahns, absolute top speed is largely irrelevant, but the handling characteristics of cars in the 70-100 mph range are regularly tested out by UK drivers, and if a car had a top speed 10 or 15 mph below that of a similar competitor, even if you would never use that speed, it would be perceived as inferior.

However, under a regime of speed limiters, you would never be able to exceed 70 mph on public roads in the UK, and unless you visited Germany you would never exceed 130 kph/81 mph which is the maximum motorway speed in other European countries. This would mean that inevitably the emphasis on speed would be reduced, and to a lesser extent handling. In a sense, cars would be more equal than before. But this is not to say that cars would become more like a 2CV, as the anti-car brigade might imagine.

The only areas where one driver could gain an advantage over another would be to out-accelerate and out-brake him within the speed permitted by the limiter. The result of this would be that cars would be optimised for strong low-range acceleration, with low gearing and very torquey engines, maybe with a much greater proportion of diesels than at present. Automatic transmissions would also become more prevalant, this combination of factors leading to increased pollution. In general, it is probable that cars would tend to be bigger, more cossetting vehicles that insulated drivers from their environment to a much greater degree than currently. The increased number of low-speed collisions could lead to them having thick, impact-absorbing bumpers all round in the manner of dodgem cars.

A particular technical point that would need to be carefully reviewed is that of speedometers. Currently, speedometers are not permitted to under-read at all, but are allowed to over-read by up to 10%. In practice, most do over-read by between 5 and 10%. Clearly this degree of accuracy would not be adequate for controlling speed limiters, and a better way of ascertaining a vehicle's speed would be needed. In fact, the trip computers fitted to an increasing number of cars give a much more accurate assessment of speed than speedometers, so it isn't difficult.

However, speeds can be increased to some extent by fitting bigger wheels and tyres, so the question must be answered how the system would cope with that. Equally, as tyres wore, the maximum speeds a vehicle was capable of would reduce. For truck tyres, this could result in a significant difference. Small, niggling differences in maximum speed between limited vehicles could be a cause of danger and accidents.

Implications for Motorcyclists

To a much greater extent than car drivers, motorcyclists see their chosen means of transport as something to be positively enjoyed, not just a means of getting from A to B, and are much more willing to speak out in defence of their rights and freedoms. Speed limiters can also potentially cause serious safety problems for two-wheeled vehicles by making them lose adhesion if power is unexpectedly restricted during cornering. To this end, a get-together of European motorcycling groups have already adopted the Mulhouse Declaration opposing any proposals that would take control of the vehicle away from the rider or driver:

We the undersigned utterly oppose the compulsory fitment to privately owned vehicles of any device designed to arbitrarily remove control from the driver to remote operation.

We note with extreme concern the tendency of governments to impose ever more intrusive and restrictive regulations upon the citizen.

We caution governments to remember that they are permitted to govern only by the consent of the people and that such consent when given through an election does not grant unlimited licence to interfere in the daily life of the citizen.

We further caution all governments that to impose unduly on popular freedom is to imperil the respect in which government and the rule of law is held.

And would limiters also be applied to pedal cyclists - although it is difficult to see how they could be? If not, how will you stop them speeding? If cyclists were regularly overtaking cars in 20 limits it would breed an incredible amount of resentment. I believe in general, since cyclists would often be blamed for speed limiters, they would end up being given much less consideration on the roads than they are now - which is much greater than militant cyclists would have you believe.

The Speed Limit Regime

Another issue is the speed limit regime into which the limiters were introduced. If at present, with 30 mph limits on urban main roads, and limits of 60 or 70 mph on motorways and most trunk roads, the use of limiters would not greatly increase journey times, although it would be an irritation to drivers and would have the negative safety implications outlined above.

However, with the general use of limiters, there would be the opportunity to further reduce limits, knowing that enforcement would not be a problem. This policy is put forward by several anti-car pressure groups who advocate a default 20 mph limit in urban areas, 40 mph on rural single-carriageway roads, and 55 mph on motorways. When it became clear that the simple introduction of limiters was not a road safety panacea, there would be strong pressure for further speed reductions along these lines. Over time we could end up with the speed limit at every location set so that the least competent driver, with the vehicle with the most limited roadholding, could safely negotiate every physical hazard at the maximum limited speed.

Yet motor vehicles can still be extremely dangerous even at 20 mph, especially trucks and buses, and the slower vehicles were required to go, the more it is likely that drivers' attention would wander. Also, in urban areas, pedestrians and cyclists would take more risks around slower vehicles. So there is no proof that even if limiters were used as a means to implement the "slower speeds" agenda in its entirety, it would do very much to reduce casualties. Generalised slower speeds would also lead to a deskilling of drivers which could to a large extent offset any gains from reduced severity of impacts.

If typical speeds on urban main roads were reduced from the 35 mph that prevails at present, to 20 mph, each vehicle would be in sight for almost twice as long, giving the impression that the road had bcome much busier. Rather than the car-free paradise they imagine in their dreams, we would end up with city streets appearing to be constantly full of a snarling, belching mass of crawling vehicles. Much more than today, pedestrians would have to judge the speed of approaching vehicles rather than waiting for them to go past, which could lead to a surge in pedestrian injury accidents, if not deaths.

And the impact on journey times resulting from the "slower speeds" policy could have a serious impact on economic performance. The quicker, more reliable journey times offered first by the canals, then by the railways, and in the past 40 years by the motorway network, have been one of the major engines of economic growth. Road congestion is now seen as a major drag on the economy - so could an increase of 50% or more on many real-world journey times put the economy into serious reverse gear?

Proponents of public transport would have to accept that many bus journey times would be significantly extended by slower speeds, allowing the car to retain its advantage in terms of door-to-door journey times.

How the Changeover Could be Achieved

Clearly it would not be possible to set a single date after which all new cars sold would have to have mandatory limiters. For one thing, this would cause huge upheaval in the motor industry, with people queueing up to buy the last cars available without limiters, and then shunning the new car market for many years to come. Sales of new cars would probably never recover to their previous level, as some keen drivers kept running pre-limiter classics, and others extended replacement cycles because they could never improve on the performance previously available to them.

Inevitably the changeover would need to be phased in, which could be done in one of two ways, or a combination of the two. Either the fitting of the limiters could be compulsory from a certain date, but their use would remain voluntary, or the speed limitation could be switched on area by area, probably starting with urban areas where least objection would be raised.

Even before the compulsory switch-on of the devices, it could be that enough drivers used the limiters voluntarily to make a significant impact on vehicle speeds. It only takes one car driving at 30 mph to hold up a long queue who want to go faster.

Compulsory retrofitting of the existing vehicle fleet would probably not be required, but it could be encouraged by giving discounts on road tax. If produced and fitted in large numbers the limiters would probably cost around 300 per vehicle.

In practice, the existence of a small proportion of non-limited vehicles on the roads would not have serious implications for safety, as on busy roads there would be a "critical mass" of limited vehicles which would restrict their progress. The fact that a few owners of classic GTis were occasionally having a backroad blast would not make any major difference to casualties.

But many people who valued that freedom - even if they only rarely exercised it - would retain classic vehicles, and might relish the opportunity to drive on roads largely freed from speed cameras and traffic calming obstacles. Inevitably there would be pressure, after a few years, to prevent non-limited vehicles from being used on the roads at all. And would you want to wreck your classic Jaguar or TVR by fitting a speed limiter, even if it was technically possible?

Other Considerations

Clearly, speed limiters would have to be introduced on a consistent, Europe-wide basis - since different countries have different speed limit regimes and there is an increasing amount of international vehicular movement.

A key issue is what the default setting in the absence of a GPS signal would be. Ideally, it should be that the limiter was not operational, as some jurisdictions (not only Germany) still have totally derestricted roads, and many people have roadgoing cars that they also use on track days. Track days would probably become much more popular as drivers wanted to test out the unlimited performance of their vehicles, and we could see the establishment of private road circuits comparable to the Nurburgring in Germany for people who wanted to enjoy "real" driving. If these then saw large numbers of accidents from drivers who had forgotten or never learned how to handle high speeds, pressure would inevitably come to ban or severely restrict them.

However, in practice the default setting would probably be no more than 30 mph, and anyone wishing to run track days where limiters were disabled would have to obtain a special licence from the government, applying over a limited area. This would raise the issue of what would happen to cars in the eastern parts of the EU if they wished to enter countries where the EU-backed speed limiter system was not in operation.

There is also the question of how the system would handle locations where a motorway crosses a road with a 30 limit, or runs parallel with it? No doubt there is a technical solution, but it might be much more complex than the basic system. Questions like these would need to be answered before the system became operational.


EVSC is a nasty, totalitarian concept, and another step towards the "Brave New World" society where our every action is controlled and dictated by the government. Even if it did save lives to a limited extent - which I strongly doubt - it would still be wrong as it takes away people's control over their own actions.

But in practice it would lead to much more dangerous roads with drivers turned into deskilled zombies, travelling around with their foot to the floor or the cruise on "max" and their attention wandering, relaxing in the misplaced confidence that with the speed limiter in operation they could do no wrong.

To quote from Neil Liversidge, Chairman of the Motorcycle Action Group, on EVSC:

This issue is not ultimately about what is or is not technically feasible; it is about what kind of world we want to live in. Think about it. It's your life, your freedom.

Don't forget - Speed limiters kill!

(last updated August 2002)

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