DfT reports says Portsmouth signage-only scheme reduces road casualties

A report in today’s Daily Mail claims to show how a Department for Transport report demonstrates “Why death rates INCREASED in 20mph zones”. It’s one of those articles that makes you sigh wearily, the way you might when faced with a wilfully contrary child. But to be fair, it’s not just us. Even the Mail’s own readers seem to be having a bit of trouble swallowing their line, at least if some of the comments below the story on their website are anything to go by.

The DfT-commissioned report entitled “Interim evaluation of the implementation of 20 mph speed limits in Portsmouth”, draws the following conclusion: “Early figures suggest that the implementation of the 20 mph Speed Limit scheme has been associated with reductions in road casualty numbers. The scheme has reduced average speeds and been well-supported during its first two years of operation.”

Fairly unequivocal then. But no, that conclusion comes in stark contrast to the opening line of the Mail’s article which states: “Reducing the speed limit to 20mph in all residential streets does not significantly improve road safety.”

We can only assume that the Mail’s Chris Brooke has contacted the report’s authors - Atkins, the UK's largest engineering and design consultancy and the world's 11th largest design firm - to tell them they have made a terrible mistake.

Brooke’s conclusion seems to have been based on the statistic for people killed or seriously injured (KSI) which the DfT report states rose from an average 18.3 to 19.9 when the figures for the three years before the scheme are compared to the two years of its operation covered by the report.

But as the report clearly explains: “Because the total numbers of deaths and serious injuries of casualties by road user type and cause are relatively low, few inferences about the scheme’s impacts should be drawn from these figures.” In other words, the figures are statistically less significant and are the kind  that could vary from year to year as a result of individual incidents (a triple fatality accident occurred in Portsmouth in the consultation period, for example) or factors such as protracted periods of  wintry weather.

More statistically significant perhaps, is the reduction in slight injuries – a far more common type of accident – which when combined with the KSI figures shows an overall 21% reduction in the total number of accidents. The Mail apparently deems this figure “not significant.”

The Portsmouth speed reduction initiative is important because it is the first time a local authority in England has implemented such an extensive scheme covering most of its residential roads using signage alone. There are no other traffic calming measures in place. The signage-only issue means the scheme is, to a large extent. self-policing, relying on motorists to recognise the benefits of reducing their speed to the wider community and specifically in reducing accidents and injuries.

The Mail, however, latches on to the figure of an average reduction in speed across the 20mph residential street zones of just 1.3mph. The article fails to point out that while many of the streets already had average speeds below 20mph due to their narrowness and the presence of parked cars, on those streets where traffic averaged above 24mph before the scheme, the reduction was an impressive 6.3. So where the need for a reduction in speed was greatest, the introduction of the 20mph limit was at its most effective.

The report should make a strong case for the wider implementation of urban 20mph zones when studied by those responsible for town planning and traffic management in other British cities. Or at least the ones who don’t believe what they read in the Daily Mail.


timlennon [210 posts] 6 years ago

Sorry, I refuse to sully my browser by re-directing to another lame Daily Mail article. It's people like you that have driven up their traffic far beyond any reasonable measure!

But, yes, absolutely: "It’s one of those articles that makes you sigh wearily, the way you might when faced with a wilfully contrary child."

Tony Farrelly [2874 posts] 6 years ago

Luckily you can also go direct to the DfT report + if you did happen to head Mailwards the comments are always good value although not as good as the first comment on their story last week on traffic congestion which blamed the problem as you might expect from a Mail reader… on lax immigration laws

swldxer [84 posts] 6 years ago

At least SafeSpeed weren't quoted!  3

mattsr [16 posts] 6 years ago

The Daily Mail:- Like spending twenty minutes in a lunatic asylum.  35

jobysp [143 posts] 6 years ago

LOL @mattsr  16

Rest assured my fellow Road.cc readers - I have some good news for you.

Based on an estimated UK population of 61,792,000 (excluding homeless and illegal immigrants) we have around 9.9 million under the age of 15 (again an estimate)

That gives us 51,892,000 people with the potential ability to understand the newspaper and make incorrect judgements and believe the 'hype'.

The Daily Mail claim their readership is 4,853,600 per week.

Multiply the 52 million (rounded up for ease) by 7, to give the total 'potential' readership for a week, gives us 364,000,000 potential readers.

This means that only 1.37% of the population (rounded up readership to 5 mil) actually read the Daily Mail.

I'm even taking the liberty of rounding it down to 1.27%, assuming that .10% just look at the pretty pictures.

So here's the Daily Mail headline:
"The Whole Of The UK Officially Reads The Daily Mail"

Kevin Steinhardt [30 posts] 6 years ago

21% reduction in KSIs and the Mail thinks this doesn't justify the 'inconvenience' of driving at 20 mph??!/!?1/1 …or is it that the Mail believes that a 21% reduction in KSIs doesn't justify the cost of changing the limit from 30 mph?

badbunny [71 posts] 6 years ago

The Daily Mail.....what more do you need to say?  37