LEAFLETS put out by the Welsh Government claiming the new default 20mph limit would only add one minute to journeys have been criticised by the official statistics watchdog.

A three-page document published on August 30 set out some of the reasons behind the change and suggested that, while the speed reduction would help to save lives, “most journeys” would only take “around one minute longer”.

But Ed Humpherson, director general for regulation at the Office for Statistics Regulation, has sent an email to the Welsh Government’s chief statistician criticising the lack of transparency of the information underpinning the claim.

A Welsh Government spokesperson has said they “welcome the letter” and implemented the OSR’s advice by making the information available online.

In the email dated Thursday, November 23, Mr Humpherson said “it would be challenging for a reader to unpick this detailed document and understand the data and calculations used to support the claim”.

The director general recommended that Welsh Government analysts “should continue to work with and support” communications and policy staff on data presentation matters.

Welsh Conservative shadow transport minister Natasha Asghar MS said the criticism over transparency made it “even more clear” the rollout of the 20mph default limit had been an “absolute shambles”.

A spokesperson for the Welsh Government said: “We welcome the letter from the Office for Statistics Regulation.

South Wales Argus:

“The figure referred to is supported by a technical document that explains how population, car journeys and distances travelled data were used within the calculation.

“We have taken OSR’s advice and have made this additional information available online.”

Where does the Welsh Government’s one-minute claim come from?

On the same day they received the letter from the OSR, the Welsh Government published a technical explanation of their one-minute figure.

They said the types of trips made on affected roads are “typically short and involve stop-start travel conditions”, making the actual impact of the slower speed limit “marginal”.

According to the Office for National Statistics, average free flow speeds on 30mph and 20mph roads are 31mph and 26mph respectively, resulting in an average delay of 46 seconds per mile.

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The Welsh Government say average speeds in typical driving conditions are 22.2mph on 30mph roads and 19.5mph on 20mph. That difference - 2.7mph - is applied to the total distance driven on affected roads (in 2019) to produce a value of a billion additional minutes per year.

They take the average number of car journeys per person per year (380, from National Travel Survey) and multiply it by the population (3.1 million) which leads to the figure of 1.2 billion car journeys by Welsh residents per year.

The one billion additional minutes is divided between the 1.2 billion car journeys, resulting in an average increase of exactly 50 seconds per journey.

Or, when rounded to provide a “reasonable worst case”, they say – around one minute.