Road Safety News

London set for 20mph blanket?

Monday 10th June 2013

A blanket 20mph speed limit could be introduced on all residential roads and high streets in London by 2020, according to the mayor’s transport advisor (Evening Standard).

Motorists could be restricted to 20mph within the M25 on all but major arteries, according to Isabel Dedring, London’s deputy mayor for transport. A 20mph limit is already in place on 19% on the capital’s roads.

A move towards a London-wide limit of 20mph is expected to be included in the Roads Taskforce, set up by the mayor and to be published later this month.

Isabel Dedring, who is in charge of the Taskforce, said: “It could be realistic by 2020. It could be one of these things like smoking (in public places) where suddenly we get to the stage where we can’t believe it would ever have been OK to drive above 20mph.

“I live in a residential road in Camden that isn’t 20mph and I think that this small road with cars bombing down is ridiculous.”

Islington recently became the first London borough to impose a 20mph limit on all the roads it controls and other central London councils are consulting residents on the same borough-wide policy. The Evening Standard article suggests that these central London councils will set off a chain reaction with Westminster, the City of London, Southwark and Lambeth also adopting 20mph.

The Evening Standard also says that the mayor plans to incentivise a shift to 20mph by funding for the necessary physical changes to the roads.

Isabel Dedring says resistance to lowering the limit - mainly from outer London boroughs - is on the wane.

She said: “The boroughs that were previously totally against 20mph are definitely softening their position. There’s recognition that residential roads are different from strategic roads, especially in outer London.

“The issue has been that the borough politicians don’t want to slow motorists down where lots of people drive. No one wants to be the person to say they are slowing all the motorists down and they can’t get to work.”

A spokesman for the AA said: “In principle we have nothing against 20mph zones although you have to remember when you are slowing traffic down you slow down the working life of the city.”

Click here to read the full Evening Standard report.


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Nick: Fair point. If the typical speed on a residential road was already significantly lower than 20 due its physical characteristics, I agree it would seem pointless to reduce it ‘officially’ to 20, but such roads are probably in the minority and it may be procedurally and logistically easier to include such roads anyway as part of a blanket treatment. Don’t forget, lots of roads already have default speed limits way above their actual speeds anyway.

However, my comment about ‘traffic not that fast anyway’ was actually referring to the overall speeds on main roads in town and cities which business/commercial traffic would normally use and where other traffic, junctions and unpredictable random impedances to flow can make journey times vary so much, that lowering of the limit would not make any difference and certainly would not slow working life as someone claimed.
Hugh Jones, Cheshire

Agree (2) | Disagree (1)

Hugh, a comment on both your posts. Firstly, if the traffic wasn't that fast in the first place, why the need for expensive measures to slow it down? Secondly, you may have guessed that I am sometimes willing to get up to higher speeds more quickly. When friends follow me they often ask if my brake lights are working properly as they don't often see them.
Nick Elmslie, New Milton

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Hats off to Rod. His phrase “…those drivers most willing to get up to higher speeds quickest are usually found to be the ones that need to rely upon their brakes most…” One of the most succinct, pertinent and true statements on driving today, I think I’ve ever read on this forum.
Hugh Jones, Cheshire

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I am not in a position to know whether that was favouritism or no. I try to keep my posts short and as appropriate as I can. Sometimes, my posts have been “moderated” but never in a way that I felt a complaint was necessary or needed public airing.

Yes, the degree in Automotive Engineering comes in handy sometimes. And you are correct in that the kinetic energy developed in acceleration can be used to defer the use of energy to overcome power train losses, rolling resistance and wind resistance. Of course wind resistance is proportional to speed squared so a vehicle at 30mph will have 2.25 times as much wind resistance as one at 20mph.

However, my observation is that those drivers most willing to get up to higher speeds quickest are usually found to be the ones that need to rely upon their brakes most. Hence turning most of that kinetic energy into heat and ultimately hot air!
Rod King, Cheshire 20's Plenty for Us

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I see Rod King was allowed 235 words - I call that favouratism!

While I am here, Rod, just one point as one engineer to the other - the extra energy you refer to when accelerating to higher speeds is then stored as kinetic energy, to be released when slowing down to take you further on less fuel than you would go from the lower speed - inertia, momentum etc, as Newton realised so many years ago. Just thought I'd mention it, as you seem to have forgotten it.
Idris Francis Fight Back With Facts Petersfield

Agree (5) | Disagree (7)

In London particularly, the idea that higher maximum speeds will increase average speeds is rather ridiculous. Time after time it has been shown that slower and calmer traffic provides far better progress for motor vehicles than the start/stop that is implicit with higher max speeds on a congested network. And, of course every acceleration between 20 and 30mph requires an additional 1.25 times the energy used to reach 20mph, with all its consequent noise and emissions.

What is also becoming clear is that strong, entrepreneurial cities are learning to unlink growth from motor car dominance and some of the most successful in Europe are doing so on a foundation of creating streetscapes for active travel. The core of many such strategies are 30km/h speed limits and the prioritisation of active travel.

And the more work is done by such city task forces then the stronger is the recognition of the need to change the “dynamics of transit” towards people and people movement rather than slavishly following the failed pampering of the low occupancy motor vehicle.

The signage issue is an important one and here current regulations are 20th century in their assumption of 20mph as the exception rather than a rule. I confidently expect this to change in the next 2 years and herald the mass roll-out of 20mph limits as the norm not only in London but the rest of the country as well.
Rod King, Cheshire 20's Plenty for Us

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I think this is a backwards step that will lead to an economic disaster. Companies will simply relocate elsewhere, which will result in more unemployment for everyone.
Phil, Kent

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There no doubt will come a day soon when all residential non route road in all towns and cities will be 20 mph and hopefully without the need for all the 20 mph signs that are currently crowding ends of our streets. The cost must be phenomenal. I hope it will stop side residential roads being used as fast rat runs through towns and by passing slower moving bottle necks on arterial roads.
bob craven Lancs

Agree (12) | Disagree (4)

It's very naive to believe that slowing down traffic in an urban environment will affect - i.e. slow down - the working life of that particular town or city, as the traffic wasn't that fast in the first place. Real world behaviour, not theoretical analysis is what matters.
Hugh Jones, Cheshire

Agree (15) | Disagree (6)

Slowing down the working life of a city is surely a vitally important point - reduced GDP and therefore tax revenue will cost far more than 20mph limits will ever save.

Equally important, the record shows that SI increases in 20mph areas - and that those who campaign for 20mph limits cherry pick favourable data and ignore adverse.

Before any more money is wasted surely we need competent, detailed and large-scale analysis of results so far, carried out by independent researchers?
Idris Francis Fight Back With Facts Petersfield

Agree (11) | Disagree (15)