New Speed Limit Proposals a Missed Opportunity
Proposed new guidance will not achieve objectives, as it continues to recommend the use of the measured average speed as the basis of setting limits.
The Government is consulting on changes to the way speed limits are set by local authorities 1
. If adopted, the new rules would replace those introduced in 2006, when the mean (average) speed of traffic replaced the 85th percentile (the speed that only 15% of drivers exceed) as the basis of setting limits. The ABD was highly critical of this change at the time, as it flew in the face of a wealth of evidence that setting speed limits at the 85th percentile level is the best way to minimise accidents and achieve compliance with the law.
In the pre-amble to the proposed new guidance to local authorities, the Government states that
"Speed limits should be evidence-led and self-explaining and seek to reinforce people's assessment of what is a safe speed to travel. They should encourage self-compliance. Speed limits should be seen by drivers as the maximum rather than a target speed."
The ABD agrees with those objectives wholeheartedly. The tragedy is that the proposed new guidance will not achieve them, as it continues to recommend the use of the measured average speed as the basis of setting limits.
When a speed limit is set at the measured 85th percentile speed of traffic, a large majority of drivers will comply with it. This brings a degree of peer pressure to bear on the inexperienced or reckless minority to fall into line. On the other hand, it is self-evident that a speed limit set at the average speed of traffic means that half of drivers will see it as being too low. Far from encouraging self-compliance, therefore, it will have the opposite effect and may, paradoxically, lead to higher maximum speeds, as there will not be the same pressure on the minority to conform.
It is also established that the drivers who have the fewest accidents are those who drive in the 80th to 90th percentile speed range, that is, the second fastest 10 per cent. Setting speed limits based on the average speed thus criminalizes the safest drivers, if they continue to use their judgement to travel at a safe speed for the conditions.
Speed limits that are set at unreasonably low levels lead not only to a high level of non-compliance — they also lead to a wider spread of speeds, increased tailgating and more overtaking, all of which can lead to a greater frequency of accidents. The ABD's response to the Government's consultation 2
once again stresses the benefits to road safety of setting speed limits at the 85th percentile level.
ABD chairman Brian Gregory concludes:
"The popular belief that lowering speed limits automatically leads to reduced speeds and fewer accidents is simply wrong. Speed limits have a role to play in road safety but they are only of benefit if set at a level that most drivers see as reasonable. The ABD will continue to press for the reinstatement of the 85th percentile speed as the basis of speed limit setting until the Government listens!"