Road Safety News

Scottish Government should reduce urban speed limit to 20mph

Tuesday 24th February 2015

The campaign group 20’s Plenty for Us is urging the Scottish Government to use its soon to be devolved powers on setting national speed limits and signage to set the national limit for restricted roads at 20mph.

20’s Plenty says the Scottish Government’s recently published guidance on 20mph speed restrictions and vision for active travel both indicate a “clear national aspiration and intention to set 20mph limits for most restricted roads”.

20’s Plenty says these “aspirations and clear economic benefits are being hampered” because of the requirement to have a Traffic Regulation Order (TRO) and 20mph repeater signs every 100 metres. If the national limit were changed to 20mph, the TRO and repeater signs would then only be required on any excepted 30mph roads.

Rod King MBE, founder of 20’s Plenty for Us, said: “As a devolved government, Scotland is in a favoured position. It can follow its neighbour in a ‘hands-off’ approach to the way community streets are shared to meet its national economic, public health and equality aspirations.

“But we suggest it should provide a progressive and pragmatic Scottish alternative that enables all of its communities to quickly move forward with a common shared value to ensure that all children and elderly have mobility options, that urban noise and emissions are reduced and to provide a firm foundation for active travel.

“MSPs should be confident that wherever implemented the vast majority of people in 20mph communities value them and see them as the ‘right thing to do’. Delivering it for the whole of Scotland will be popular and effective.”


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More to the point, why has the topic suddenly switched to fuel consumption and engine efficiency anyway?

By driving our cars on the roads in the first place, it's surely taken as read that we are going to be consuming fuel at different rates in varying circumstances - usually beyond our control - and we accept this as part and parcel of being the car driving public, so I'm not sure it's the most important aspect of the subject of trying to lower speeds in residential areas.
Hugh Jones, Cheshire

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Answers to your questions

1)Because I quoted the whole article as it appeared in the Telegraph including the quotes from the respected and experienced automobile engineer doing the tests.

2. Because I respect Peter de Nayors findings far more than Bob's anecdotal observations based on following a funeral procession!
Rod King, 20's Plenty for Us

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Why is Rod King discussing fuel consumption at an illegal 90mph? And why does he continue to cherry pick from one study when real world examples from all of us prove it to be of doubtful value?
Eric Bridgstock, Independent Road Safety Researcher, St Albans

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Yes but Rod they didn't test a Skoda Superb diesel automatic.1.9 Tdi...did they?

I agree that low revs aid smooth comfortable driving. Of that I am not at issue. It's obviously then the mistake of my manufacturer to place the gearing absolutely wrong at the 20/21mph mark so that instead of a quiet smooth engine doing 1200 revs I have one doing 1800 and ready, very ready to change up a gear.

The tests carried out that you mention would have been on a track. A continuous circuit and therefore one that does not require the vehicle to stop and start or ever slow down. Now that can make like for like at speed comparisons but doesn't give the whole picture. It's not just speed that's involved, it's the gearing. Different gearing will produce different results. At one time we had cars with 4 gears and found them perhaps too revy so we put a fifth or overdrive gear in and they became smoother and general with less revs we get more economical. Now we have cars with 6 gears and some with 4 wheel drive so its not merely size of engine or carb or fuel injection, it's also in the gearing. The lower the gearing the smoother the ride will be and the lesser the demand for more fuel.
Bob Craven Lancs....Space is Safe |Campaigner.

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I have already pointed to the article. But to save you clicking on the link it said:

As motorists battle against rising fuel prices, saving money could prove to be more effective than roadside cameras when it comes to keeping within the speed limit.
Research commissioned by What Car magazine has challenged the popular idea that a car is most efficient at speeds between 50 and 60 mph. Tests on five different cars ranging in size from a 1 litre Toyota Aygo to a 2.2 litre Land Rover Freelander found that the most efficient speed was below 40 mph for all five and as low as 20 mph for two. Above 40 mph, fuel consumption rose sharply and by 90 mph the average miles-per-gallon had halved.

The cars were fitted with a fuel flow meter at Millbrook in Bedfordshire, by Peter De Nayer, a former AA fuel efficiency expert. Mr De Nayer said: "There is a huge misconception that the most fuel-efficient speed is around 55mph. The study shows that the slower you go with the vehicle running smoothly, the less fuel you will use."

A Citroen C4 1.6 diesel achieved 99.6 mpg at 20 mph, but just 29.3 mpg at 90 mph. A driver of an average car travelling 10,000 motorway miles per year would spend £518 more on fuel than if he had driven the same distance at 60 mph.
Rod King, 20's Plenty for Us

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Thank you once again for your advice Rod. My car is 10 years old and not as you suggest as old as you or I. I purchased it to save on fuel not price but as a conservation measure and at the time diesels were being supported and suggested by the government of the day. I do pay excise duty...... a lot of it.. Show me a car that will do 99 miles per gallon on the road and I will show you pigs that fly.
Bob Craven Lancs...Space is Safe Campaigner

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Obviously your car is a classic and so you at least get the benefit of not having to pay any VED. And if its not a classic, then certainly it sounds like its time to get it serviced. Alternatively change it for a Citroen C4 and get 99 mpg!
Rod King, 20's Plenty for Us

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About the increase tax on fuel situation Rod so kindly mentioned, pointing out that I had not mentioned it. I have now obtained Empirical evidence that it is true. More fuel used and therefore less MPG and thus more petrol consumption in 20 mph areas.

This came about following a hearse at 20 mph to the crematorium today. At that speed my vehicle, an automatic, is still in first gear and the revs are quite high at 1.800 rpm. With the slightest of acceleration to 22 mph my vehicle changes gear to 2nd and the revs come down to just over tick over at 1.200rpm. This represents a miles per gallon diferential from 36 mpg at 1.200 rpm down to 24 mph at revs of 1.800.

That being so I will no longer benefit from the advantage diesel fuel gave me and be back to the old 24 mpg I got on a petrol car. The only good thing is I will obtain more Morrisons petrol and get the £5 gift voucher more often. Once again thank you for pointing that out to me Rod.

PS The only way around this is for vehicle manufacturers, who are used to manufacturing vehicles taking into account the 30mph (50kph) speed limits will have to gear the vehicles differently.
Bob Craven Lancs....Space is Safe Campaigner

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May I add St Albans to Paul's list. Air Pollution in part of the 20 mph zone exceeds EU Limits. May I add to Idris's comments by saying my BMW (fitted with a MPG gauge) gets best mpg at high smooth speed on motorways and worst mpg at slow speed pottering around urban areas. Hence it contributes more pollution to St Alban's 20 zone.
Robert Bolt, St Albans

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Take a read of this article which I have referenced before.


It debunks the idea that cars are most efficient in mpg at higher speeds.
Rod King, 20's Plenty for Us

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Does Rod King have special dispensation to go way over the word count we more mortals are allowed? What cars do 50 to 68mpg at 20mph? Mine average about 15! And very noticeably less than at 30, 40 or 50mph. And wrong again, if fuel consumption in mpg is lower at 20mph then "fuel injected into your engine" will be higher. Are you not aware Rod, that maximum efficiency if IC engines occurs well up the power band, not right down at the bottom end, crawling along? Because pumping losses friction, tyre flexing etc. form a much higher proportion of the work done? And that it is air resistance almost alone that prevents maximum mpg being at 60/70/80 mpg with modern cars?

Most large-engine cars will do 20mph in top gear with hardly any pressure on the accelerator, changing down and increasing rpm to maintain the same speed will burn extra petrol not less. When circumstances allow I drive my cars that have mpg displays at steady speed on level roads - max mpg is at 49-50mpg. My V12 Jaguar averages 22mpg on a motorway run, around town 15mph.
Idris Francis Fight Back With Facts Petersfield

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Oh and yes Rod I did forget.....It will also be a XXX on the motorists as well. Thanks Rod for reminding me.

On a more serious note I notice that you feel that I am muddying the waters by what I said about the antics of authorities.

Whenever there is a change that needs to be taken place and one that would be generally unacceptable to the public and there would be some degree of resistance, let's say a move from position A to E, the authority will cloud or fudge or indeed muddy the issue in a number of ways. By propaganda, selective statistics or information, emotional blackmail, involvement of other organisations that appear independent to put forward certain details supporting that move that would belie those concerns. The authority may also move from A to E slowly via B, C and on to D to make the move more palatable.

No one is ever going to admit that this happens particularly if they are close in some way to the government or authority. This might be construed as correct on my part and dismissed as rubbish.

That will make it difficult to agree or not to agree with. Is it correct or rubbish.
Bob Craven Lancs....Space is Safe Campaigner

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I was merely trying to inject a little humour into the forum! carpets..pillows..'blankets'. Too subtle?
Hugh Jones, Cheshire

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I think you have to remember that the use of the word "blanket" is a classic anti-20mph tactic. Whilst we, and I think most people, advocate a default 20 with exceptions, the use of the word "blanket" conveys a very different intervention.

Adding the word "ban" is also particularly effective in stirring up concern. Further talk of authorities "playing games with drivers" is another good attempt to muddy the waters. However I do notice that Bob hasn't resorted to the classic of mentioning the "xxx on the motorist".

Have a good weekend everyone!
Rod King, 20's Plenty for Us

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Maybe not so out of context Bob... after all, it is about 'blanket' 20mph zones.
Hugh Jones, Cheshire

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OK in a moment of early dementia I wrote carpet instead of cushion. It's all just a load of soft furnishings and within context not detrimental to the overall piece. Why did they call them cushions in the first place, why not pillows? More appropriate I would have thought. lol. Thanks for pointing it out though Hugh, appreciated. Will try better next time.
Bob Craven Lancs Space is Safe campaighner

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Carpeted highways? You must live in a very select area Bob!
Hugh Jones, Cheshire

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Your argument fails just on one obvious point. You clearly state that what you propose is a blanket (wide area) 20mph speed restriction in all towns, cities and villages. This is what this Government wants also. On that note I applaud and congratulate you for your efforts and being honoured by this Government and on being awarded the MBE in recognition of your work and the supporting of their adopted road safety measure.

If what you propose comes to fruition then there is no need for passive measures such as humps or rugs/carpets etc. that have to negotiated or avoided.

However, and this it where it fails, the authorities are not going for a blanket ban but on selective restrictions. At the present time it's a mish mash and piecemeal throughout a number of towns and cities and villages. This has in many cases caused the implementation of all the passive measures available.

Driving opinion is not yet there and authorities are playing the game of making it difficult for drivers and will continue to do so until drivers have had enough, are confused and reluctantly accept the proposition.

One of your arguments for its implementation is (emotionally) for the safety of kids to play out on their streets as happened in my and your younger days, but it won't happen. There are too many parked cars to make that the least bit viable.
Bob Craven Lancs...Space is Safe Campaigner

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Would anyone agree that slowing traffic down is not the whole answer? Statistics show that by far the majority of collisions are vehicle to vehicle ones, generally where vehicles are in close proximity and driving under the speed limit anyway. As I see it if we do slow them then they will still drive too close together, or indeed closer, most drivers presuming that when the brake lights come on in the vehicle in front then they can also apply brakes and stop in the same time and distance.

This is the presumption of many drivers and they fail to take into account the advice in the Highway Code that it's the overall stopping distance that should adhered to and not just one part of it, ie. the braking distance. They fail to realise that thinking time should be included as well. Perhaps this is the reason we have so many shunt accidents at junctions and on motorways. A lack of understanding of what a safe distance is.

When distance is understood then the roads will be a lot safer place, traffic will travel smoothly and courtesy will occur. No one will be SUPRISED by a vehicle coming into close proximity as it will have been observed earlier and avoided before it has the chance to get to close.
Bob Craven Lancs....Space is Safe Campaigner

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Dear Road Safety Professional

Hopefully, without boring you and without adding to any emissions Hugh, I can provide some enlightenment after Paul Biggs' comment.

Yes, a "campaign group", that you claim doesn't understand road safety, or emissions or have "any driving or road safety expertise". Well, we do our best to work from an informed position. I have nearly 50 years driving experience, an honours degree in Automobile Engineering, 7 years working as a design engineer for Ford Motor Company, an MBE in Services to Road Safety and last year completed a Road Safety Practitioners course with RSGB. We also have knowledge of and work with all the local authorities who have real experience of implementing their own 20mph limits.

We would encourage readers to look up the AA press release. It tells us what we already know and that is that at a steady 20mph or 30mph then fuel consumption can vary by about 10% 52 vs 68mpg. Other tests show this 10% variance can be positive or negative as well.

What it also shows is that having a 20mph zone with speed bumps and cycling between 20mph to go over the bumps and (illegally) speeding up to 30 between them raises consumption! Hardly surprising!

But as this is both illegal and not what we propose (ie we advocate wide area limits without necessarily physical calming) it is hardly relevant. We debunked this AA press release in 2008 and this may be viewed at

I suspect that any pollution in those Bristol points is due to the congestion and not a steady speed. Hence not relevant. Imperial College London investigated 20mph limits and found there was no detriment to air quality.

Whilst your engine speed may be the same at 20mph or 30mph, the amount of fuel injected into the engine will be less as 20mph. Hence on its own your statement is not an indicator of any increased emission.

In 2013 the casualty figures for 20mph roads included may roads which were 30mph in 2012. Hence any increase in 20mph casualties and reduction in 30mph is entirely predictable and not an indication of increased risk.

And whilst you say that vehicle speed does not effect transport mode choice this is contradicted by surveys conducted.
Rod King, 20's Plenty for Us

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"It's long been established that 20mph can increase emissions". Talking about it certainly seems to produce a lot of hot air.
Hugh Jones, Cheshire

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Here we go again! Yes - 'campaign group' - not a group that understands road safety or emissions or has any driving or road safety expertise. How do they continually get away with making such false claims? It's long been established that 20mph can increase emissions e.g. AA Report 2008

Plus, e.g. new (2013) 20mph limits in Bristol on Blackboys Hill and Whiteladies Road are the only 2 places that exceeded EU air pollution limits in 2014.

My engine turns over the same rpm (1500) at 20mph (3ed gear) and 30mph (5th gear) although tyre noise/wind noise may be reduced.

DfT 2013 casualty figures for 20mph limits: 3 less fatals but a 20% overall increase in casualties. 30mph limits: 59 less fatals, 7% overall reduction in casualties.

20mph is still 5 times faster than walking pace and keeps drivers in their cars for longer. There's no logical reason why a speed limit would affect the transport mode choice.
Paul Biggs, Staffodshire

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