...or why unrepresentative data is not reliable.

If you don't have a TomTom device in your vehicle then you may be surprised that if you live in one of the places recently researched by Atkins for the their Evaluation of 20mph limits then it doesn't matter how much you keep within the speed limit your considerate driving was completely ignored. And you wouldn't be alone. The report estimated that the actual number of drivers who were also ignored were in the 97% of vehicles who's speed they never measured.

Atkins and DfT decided that in order to gather information on vehicle speeds in 20mph streets in 12 case study 20mph areas and compare them with 3 other 30mph areas then they would use data captured from high end TomTom SatNavs or vehicles with in-built TomTom in-car devices. This is termed Floating Car Data (FCD).

You may therefore wonder just how accurate and representative their statistics and research were if it only included 3% of vehicles. We did as well, so we did some of our own research.

Today the government published its long awaited report evaluating 20mph limit implementations. We welcome the report. It has been a long time coming since 2014 when it was commissioned.

And in that time there have been nearly half a million casualties on streets with a 30mph limit.

The report only evaluated a small number of case studies which in themselves only covered part of an authority. There are some useful indicators in the report, particularly around the negative aspects of police failing to routinely enforce 20mph limits and the need for national engagement and awareness on the benefits of reducing speeds below 30mph in residential and other roads.

However, we have major reservations about the primary data used in the report around speed reductions and the complete failure of the study to look at sufficient casualty figures to be able to draw any conclusions that would be statistically credible. These were key reasons for the commissioning of the report and we are amazed at the choice of data measured which appears to be based on measuring what is available rather than what is meaningful. 

Here are the 60 second videos we recorded at our 20's Plenty for Wales Conference from presenters and delegates.

Note that this page may take a while to load.

A sell out conference of 100 delegates met in Cardiff to share best practice on how to make streets healthier in Wales by reducing road risk at source through 20mph limits with a focus on 20mph as a national urban default.

Click on each presenter to open their presentation or 60 second voxpop

I was delighted to be asked to speak at the seminar held in the Scottish Parliament building to discuss the private members bill for changing the national default limit for restricted roads in Scotland to 20mph. Local Authorities would be able to make appropriate exceptions where a 30mph limit would be retained for certain roads.

The text of my presentation follows :-

Top 10 questions answered
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The University of the West of England (UWE) has analysed the impact of 20mph roll-outs for Bristol City Council. It finds reductions of 2.7mph in average traffic speeds and an estimated cost saving of over £15m per year from fatal, serious and slight injuries avoided.

Councillors and council officers don’t always tell the truth on 20mph limits. Here we bust some more of the common myths. See also part 1 http://www.20splenty.org/council_myths about A and B roads, current average speeds over 24mph, unsupportive police and collision history.