Beware Irrelevant DfT Data on Speeding in 20mph Limits.

Blog by Anna Semlyen 20’s Plenty for Us National Campaign Manager June 2019

At the end of June, the Department for Transport (DfT) report some irrelevant statistics on speeding[1]. Note firstly that the 10 sites of 20mph roads are unrepresentative free-flow locations with no traffic calming or other speed restricting features which tend to be through-roads.  Yet most 20mph limits are side roads.



The DfT specifically states that you cannot extrapolate from this data to make general comments about compliance. The sites “are not representative of the level of speeding across the whole road network – which we would expect to be lower.” Further “quieter residential streets which may make up a large proportion of 20mph roads will be under-represented in the data”.

The DfT headline figures seized on by those anti-20mph are that, under free flow conditions 87% of cars exceeded the 20mph limit. 22% exceed the speed limit by more than 10mph.

The 20’s Plenty rebuttal is:

  1. It’s no surprise that few drivers comply with a 20mph limit in freeflow conditions on atypical 20mph limited through roads. 20’s Plenty for Us disagree with both the choice of 20mph sites used and freeflow way of recording them.
  2. Whilst opponents say drivers can read the road and know better what a safe speed is we say that a civilised society doesn’t and shouldn’t let drivers decide limits.  We demand safety for the vulnerable based on our human capacity to withstand a crash. A 20mph limit is crash survivable for a pedestrian or cyclist. The key issue is what’s the right limit, not how many drivers obey it. Science say 20mph is the maximum where vulnerable road users mix with motor traffic.
  3. Compliance isn’t just about the limit number - but partly about social norms, education and enforcement.
  4. When a survivable limit of 20mph is set more widely, compliance will rise due to it becoming normal.  For most of the UK 30mph is still normal and 20mph the exception - so 20mph feels slow when driving as most people learnt at 30mph. Drivers flouting limits isn’t the cause of the problem. It’s a symptom.
  5. Driver compliance is a hearts and minds issue as there isn’t yet enough police or camera enforcement so it must be socially enforced on each other.
  6. Within the next 3-5 years in car speed limiters will be used in sufficient cars to set the pace behind. Speed limiting is a game changer on compliance and then 20mph really will be 20mph limit. No need for cameras, humps etc when the limit is enforced in car.

In summary, the DfT 20mph speeding data is simply not relevant to any debate on 20mph limits in residential and high streets. That drivers aren’t complying on atypical sites, doesn’t negate the need for 20mph to become the normal UK built up area limit. A consensus of politicians in Wales have agreed it will go 20mph. It’s leaders ‘get it’.  20mph is a win-win for everyone and drivers will be most likely to obey it once it is normal.


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