April 1999

Key Points

Local authorities must not be allowed the power to set 20mph limits wherever they like, as many of them will certainly abuse this power by introducing inappropriate 20mph zones as part of their "traffic restraint" measures to make car use unattractive compared with other modes of transport. There has already been significant abuse of 20mph zones, as well as widespread abuse of the right to introduce 30mph, 40mph and 50mph limits on rural roads, by anti car local authorities, and this has been shown to be detrimental to road safety.

Strict and legally enforceable guidelines must be set up describing in exactly what circumstances a 20mph zone can be introduced. These should cover width of road, density of residential access and peripheral visibility.

Local authorities must not be allowed to use road safety as an excuse to bring in measures really aimed at making car use unpleasant.

Summary of Arguments

  1. In urban areas drivers are constantly required to vary their speed by the prevailing circumstances. A safe speed in any one location can vary between 5mph and 50mph, depending on time of day.
  2. The nature of these locations means that a 20mph zone is often not a suitable way to improve safety
  3. Inappropriately applied 20mph zones will be bad for road safety, especially if rigidly enforced.
  4. Government claims as to the casualty reducing effectiveness of current 20mph zones are statistically invalid.
  5. There has been considerable abuse of 20mph zones which have been inappropriately applied as traffic restraint measures, even when consent from the Secretary of State has been required.
  6. There has been wholesale abuse of the power to reduce speed limits since councils were allowed to ignore limit setting guidelines.

1. The determination of appropriate speed — Why 20 mph?

Urban speed limits are necessary to ensure that drivers travel at a speed which allows those who are driving with proper care and attention to avoid the hazards they are likely to encounter due to mistakes by other road users, be they pedestrians, cyclists or other drivers.

They must, as far as possible, be set at levels which actually relate to the hazards that are likely to be encountered. When we are looking at the difference between 30mph and 20mph, accidents involving loss of control of the vehicle or driving at a speed where braking distance is out of line of sight are highly unlikely. The kind of accident we are seeking to avoid is therefore one in which the braking distance is unexpectedly invaded by another road user, unseen until it is too late. This is often exacerbated by an absence of manoeuvring space, leaving the driver nowhere to go to avoid the collision.

This quite clearly defines locations in which a 20mph (or less) maximum speed is appropriate as those where peripheral visibility is seriously constrained by parked vehicles or buildings and where the road is reduced to a single vehicle width. This scenario covers many typical urban accidents: the child running from behind the parked car, the ice cream van, the cyclist who does not look, the oncoming vehicle rounding an obstruction, the stationary bus, the car pulling out of the side street, the car that fails to give way at a crossroads or badly sited mini roundabout.

Where peripheral visibility is not thus obstructed, similar accidents are not caused by the vehicle's speed but because the driver has failed to see the other road user — he fails to take any evasive action at all despite having plenty of room to stop from the speed he was doing. A lower speed may well reduce the level of injury, but it will not avoid the accident. Seeking to enforce a lower speed in such circumstances is simply perpetuating the real cause of the accident — bad driving — whilst penalising those who are paying attention and thus not causing any hazard. This is very poor road safety policy.


2. The suitability of 20mph zones — When should they be used?

Many situations where 20mph is sometimes an appropriate speed are not suitable for 20mph limits because they are: Many places which require slow speeds are so obviously hazardous that almost all drivers drive at less than 20mph without the need for a limit. One of our members has children attending a school in a small village in Worcestershire, which comprises single track roads twisting between a collection of buildings. With no lighting, the limit in this village is 60mph — a fact which is reinforced by the presence of derestriction signs when one enters the village off the bypass, which has a 50mph limit! However, no-one drives through this village at more than 20mph (except on one stretch of wider road where they reach 30mph), because the hazards are obvious. It is also clearly defined where the village begins, with the narrow roads starting immediately. Limits are therefore irrelevant in this village.

These two factors clearly show where a 20mph zone is useful: On a road which is:

  1. Residential
  2. Single track with restricted peripheral visibility down the entire (or, at very least the bulk) of the length of the restriction
  3. The nature of the hazard is not obvious to approaching drivers, leading to a high proportion of traffic attempting to negotiate the hazard at an inappropriately high speed.
There are comparatively few such locations, but they do exist, making 20mph limits useful if applied sensibly.


3. The pitfalls of inappropriate 20 mph limits

It is well documented that limits that are set at too low a level are detrimental to road safety.

A speed limit, whether compulsory or not, is the most powerful method of advising a driver of the spread of hazards he is likely to encounter on the road ahead. At least, it should be. However, badly set limits will not only discourage compliance, they will undermine respect for all limits, even where they are necessary and correct, thus negating their primary safety purpose.

Many situations where drivers do end up travelling too fast for the conditions are as a result of an inappropriately low limit on adjacent roads. Thus, when the road conditions change and the hazard level increases, there is no change in speed limit to warn the driver that this is happening.

If 20mph limits are to be of use in the most hazardous locations, it is important that they are respected. The fact that 90% of police officers, magistrates and driving instructors often ignore 30mph limits is not a good starting point, and shows that 20mph limits must be handled very differently if they are to have any effect other than to be ridiculed by the general population.

But 20mph limits have another problem if they are set unreasonably and rigidly enforced. It is virtually impossible to drive a vehicle at 20mph when road conditions dictate a higher speed and still maintain a proper level of concentration and attentiveness on what is going on around. Currently, 20mph limits are largely enforced by traffic calming measures, which means that even though drivers' attention is focused on them rather than on scanning for real hazards, at least the driver is concentrating on something outside the vehicle. If 20mph limits are to be enforced by the normal methods, then the focus of concentration will be on the speedometer only — lunacy in an urban environment.

The sheer folly of encouraging this kind of behaviour can be gauged from the accident statistics. In 1995, there were 18,138 child pedestrian injuries in built up areas. According to the DETR, in 20mph impacts 5% of child pedestrians are killed, which would equate to 907 deaths if all the impacts happened at 20mph. Since the actual number of urban child pedestrian fatalities in that year was 106, it is clear that forcing people to drive at an inattentive 20mph rather than allowing them to gauge speeds for themselves by paying attention to the road conditions has the potential to bring about another 801 child fatalities.


4. The figures claiming success for road safety measures don't add up!

The ABD does not accept that 20mph limits are proven to reduce casualties by dramatic amounts. The same claims are made for speed cameras, traffic calming measures and speed limit reductions as well as road engineering improvements, probationary driver schemes and passive safety enhancements. And yet, the overall road casualty figures have not significantly improved since 1993. Figures claiming great improvements for certain measures must be viewed in the context of the overall figures, and when this is done they simply do not add up. There are several obvious factors which do not appear to have been taken into account:


5. 20mph zones — A record of inappropriate use already

Although appropriate 20mph zones do exist, it has been clear from the start that some councils have been using them to discourage traffic from certain roads as part of a "traffic restraint" policy. Examples are: These are all clear examples of 20mph zones being abused to solve political problems with residents who complain (usually hypocritically) about non local traffic. They are not justified on safety grounds, despite being introduced right at the beginning of the 20mph zone experiment, and have been introduced purely to annoy road users into choosing another route. 20mph zones are thus discredited before they even become widespread.


6. Many councils are introducing unjustified limit reductions, showing they cannot be trusted with 20 mph zones

Many councils are undertaking speed limit reduction programmes in complete violation of well proven, safety related guidelines for setting speed limits. They are doing this against the advice of the local police, who, in some cases, have refused to enforce the new limit, and ignoring any objections they receive from members of the public, however well informed and sensible those objections are.

If they cannot follow safety related guidelines for setting limits, how can they expect people to comply with them and how can they justify enforcing them on safety grounds?

Particularly bad are Oxfordshire, Surrey, Devon, Hampshire and Solihull, but two particular case studies illustrate the attitudes well.

It is quite clear that these councils are pursuing policies based on speed reduction for its own sake — they seem not to care at all whether there is any safety justification for their actions.

In the light of this evidence, the ABD would strongly suggest that councils are abusing their power to set speed limits. The last thing they should be given is more freedom in this area. Rather they should be forcibly constrained by sensible national guidelines for speed limit setting so that we can have limits that are reasonable, consistent and above all, based on sound, established road safety principles.