20 mph – yes we can!

This article was published in 2010, in Newsletter 88.

20 mph sign

In 2006 the Department for Transport issued new guidance on setting speed limits on local roads. 
For the first time this enabled local authorities 
to introduce significant 
areas of 20 mph limits without the need for traffic calming. It recommended that such areas should already have average speeds below 24 mph, but DID NOT rule out their introduction where speeds were higher, although it recommended that should 
speeds remain high, measures be taken to reduce them.

In Cambridgeshire, it was several years before the County Council adopted this new guidance, and it is only later this year that the first 20 mph zones under these new rules will be introduced.

From March 2008 one local authority, Portsmouth, bravely introduced 20 mph limits on a very significant number of residential roads including many where average speeds were over 24 mph.

Previous studies suggested that speed reductions of about 2 mph could be expected when 20 mph limits were introduced, but of course, under the pre-2006 guidance average speeds had to be low before introduction…

The first reports from the ‘Portsmouth Experiment’ were announced late last year, and average speeds on roads had dropped by some 2 mph, but many roads in the area already 
had average speeds of well under 24 mph. What was NEW is that on those roads where average speeds had been over 24 mph the AVERAGE speeds had been reduced by 7 mph.

In December 2009 the Department for Transport, quoting 
results from Portsmouth, proposed further revisions for the guidance on setting local speed limits, encouraging much wider use of 20 mph limits:

Further benefits of 20 mph schemes include quality of life and community benefits, encouragement of healthier and more sustainable transport modes such as walking and cycling. There may also be environmental benefits, as generally, driving more slowly at a steady pace will save fuel and carbon dioxide emissions, unless an unnecessarily low gear is used.

Based on this positive effect on road safety, and a generally favourable reception from local residents, we want to encourage highway authorities, over time, to introduce 20 mph zones or limits into streets which are primarily residential in nature; and into

  • town or city streets where pedestrian and cyclist movements are high, such as around schools, shops, markets, playgrounds and other areas;
  • where these are not part of any major through route.

The introduction of widespread 20 mph areas encourages more people to walk and cycle, increasing the independence of those too young or old to drive, yet studies in London suggest that crashes involving pedestrians and cyclists fall significantly despite their increased numbers.

Wouldn’t such limits costs lots of money to introduce?

NO. By introducing a single traffic regulation order (TRO) over a very wide area, with a second TRO setting a 30 mph limit on main roads within the area, administrative costs can be vastly reduced. Of course, signs are required where limits change, and on some roads ‘repeater’ signs are required. Traffic calming on just two residential roads in Cambridge cost £75,000, whereas Portsmouth introduced 20 mph limits on 1,200 residential roads for less than £500,000.

Residential streets such as Oxford Road benefit from the 
pleasanter environment that results from lower speeds of 
motor vehicles.
Image as described adjacent

Didn’t the AA say that fuel consumption would be increased on such roads?

Yes, but that was ‘bad science’. They quoted ‘constant speed’ figures for fuel consumption. Who could drive in either a 20 or 
30 mph area at a constant speed? When figures for a typical ‘urban cycle’ are used, significant reductions in fuel and hence CO2 are achieved in 20 mph areas.

Will it get widespread public support?

75% of people consider 20 mph right for residential roads – 72% of drivers also (British Social Attitudes Survey 2005).

30 kph (19 mph) limits have been in widespread use in many European countries for years, and it is to those limits that many attribute not only the higher levels of walking and cycling in 
those countries but also the reduced rates of injuries to walkers and cyclists.

The Department for Transport expects to confirm the new guidance on local speed limits in the next few months. We hope that Cambridgeshire County Council will adopt the new guidance as policy, and that residential streets and villages will thus benefit from the more pleasant environment that results from lower speeds of motor vehicles.

Jim Chisholm


www.dft.gov.uk/pgr/roadsafety/speed-limits (Update of guidance on setting local speed limits)

www.20splentyforus.org.uk (20’s plenty for us)