London, 17 Aug 2006.
For immediate release.

Contact the ABD

Press Release

Government Ignores Police Concerns in Changing Speed Limit Rules
Road safety group, the Association of British Drivers, has learned that a key change to the rules for speed limit setting, announced recently, was opposed by a 2-to-1 majority of those police forces that responded to the government's consultation on the issue.

Under the new rules, issued in a government circular earlier this month [1], speed limits will in future be set on the basis of mean (average) vehicle speeds. This tears up the scientific basis on which speed limits have been set for nearly 40 years. Research from around the world shows that the most respected and effective speed limits are those set at a speed that only 15 per cent of drivers would exceed if there were no limit -- the "85th percentile" speed. It has also been found that drivers travelling at around this speed have the lowest accident involvement [2].
Changing to average speeds will result in lower speed limits being set, meaning that half of all drivers, including the safest, will be acting outside the law if they drive normally.
It now emerges that the government has decided to go ahead with this change, despite opposition from the police. The results of a consultation into the proposed changes have been circulated to all those organisations that made their views known [3]. Of the 18 police forces and police organisations that responded to the consultation, 11 opposed the change to mean speeds as the basis of speed limit setting, with only five in favour.
The reason for the police objections is that the new rules will lead to lower speed limits being set, which will mean there will be less self-compliance and a need for greater enforcement.
ABD Policy Director, Mark McArthur-Christie, comments:
"The organisations with arguably the best knowledge of how speed limits work in practice — the police — have voted decisively against a change to mean speeds for speed limit setting. It is another example of the arrogance of this government that it thinks it knows best and has decided to go ahead anyway."
The government justifies the change to mean speeds because of the claimed "well proven relationship" between average speeds and accident frequency. In fact, this claimed relationship is based on a couple of desk-top studies carried out in the 1990s, in which accident rates were compared on roads of similar type but with different average speeds. However, when similar roads have different average speeds, this is because they have different traffic flows, and accident rates are affected by changes in traffic flow. For this reason, the Transport Research Laboratory has recommended that "...roads with very different flow rates should NOT be studied together" (original emphasis) [4].
The government's lack of understanding of how speed limits affect road safety is summed up in its new guidance, where one of the aims of the new system is to have "...all vehicles moving at speeds as close to the posted speed limit as possible." As Mark McArthur-Christie explains:
"This shows the government's nanny-state tendencies, by assuming that drivers are incapable of thinking for themselves and must be constantly regulated. But even well set speed limits are only a rough guide to what may be a safe speed under a particular set of conditions, and drivers need to vary their speed as those conditions change — and reduce their speed to well below the limit when necessary. Most drivers are capable of doing this successfully, but those skills are eroded if drivers are encouraged to offload their responsibility and slavishly drive at the posted speed limit regardless. Switched-off, zombie drivers are dangerous drivers."

[1] Department for Transport Circular 1/2006, Setting Local Speed Limits.
[2] An explanation of the way speed limits should be used and the background to the 85th percentile speed for setting speed limits can be found at
[3] Department for Transport decision letter following consultation on new guidance on setting local speed limits, August 2006.
[4] Published Project Report PPR026: Accident Analysis on Rural Roads - A Technical Guide. Transport Research Laboratory, 2004. (Quote taken from para 4.15)
Notes for Editors