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Campaign against 20 MPH speed limits


As shown in studies of 20 MPH zones, the average traffic speed reduction after putting up 20 MPH speed limit signs is typically about 1 mph. That's not enough to have any impact whatsoever on pedestrian or cyclist casualties and not enough to be noticeable by road users.

Indeed a report from the Department for Transport (DfT) in 2017 showed that the vast majority of drivers ignore 20 MPH speed limits. A survey of nine sites across the UK showed that 81% of drivers exceeded the 20 MPH speed limit in the report entitled "Speed Compliance Statistics". This might explain why the impact on average speeds by introducing signed only 20 limits is negligible or that the impact on actual accident statistics as reported in many such zones is also not apparent.

Surely the message here is that imposing unrealistic limits tends to be ignored by drivers. Experienced drivers drive at a speed that is appropriate for the road conditions and keep their eyes on the road, not on the speedometer. The ABD has always supported setting speed limits at the 85th percentile of free-flowing traffic speeds so that only those drivers who are clearly not adhering to what most drivers perceive as "reasonable" are potentially penalised for breaking the law. In addition, it has been shown in other studies that setting the limit in that way is likely to be safer than artificially reducing the limit.

But putting up 20 mph speed limits which are then ignored generates calls for more enforcement, and it gives the police an opportunity to make money by diverting drivers to speed awareness courses which also finances more speed cameras. The ABD has a separate campaign called AMPOW which is focused on that perversion of justice which you can read about here: www.speed-awareness.org  

The ABD does not oppose 20 MPH speed limits where they are justified - for example in narrow roads with large numbers of pedestrians and where average traffic speed is already near 20 MPH. But reducing speed limits on such roads is unlikely to significantly reduce road casualties and therefore the cost/benefit ratio for such interventions is poor. In reality it's better to spend the money available on other road safety measures rather than on putting up 20 MPH signs.

We hope we have shown in this web site that the introduction of 20 MPH speed limits has no cost/benefit justification and is unjustified by the claimed benefits.

If you agree with us please register your interest by registering your interest in the campaign here: