Firstly traffic authorities have the power to introduce 20 mph speed limits and zones without obtaining consent from the Secretary of State.

Speed Zones refer to a collection of streets with a 20 mph limit whilst Speed Limits are set for individual roads. Some local authorities have set 20 mph speed limits on a number of individual roads so creating a blanket coverage of residential areas with a 20 mph speed limit.

They should not be implemented (according to Dft Circular 01/2006) on roads with a strategic function or on main traffic routes.

Whilst 20 mph speed zones do require some sort of traffic calming, this need not be physical. There is no mandatory requirement for speed bumps. Build-outs, road marking, signs and rumble strips can all be used to calm traffic speeds in 20 mph speed zones.

20 mph speed zones are indicated by specially designed zone entry and exit signs.

On the other hand, 20 mph Speed Limits can be introduced without any form of traffic calming. Even without such measures, just introducing a limit alone has been found to reduce speeds by 2 mph. Now considering that every 1 mph reduction in speed reduces accidents by 5% then this provides very good value for money. Of course the effectiveness of default 20 mph Speed Limits is increased by publicity, driver awareness and community involvement. This can and does play a large part in self-enforcement.

20 mph speed limits are indicated by terminal speed limit signs and repeater signs at regular intervals along the roads. These are cheap and easy to install on lamp posts.

If your local authority is saying that speed bumps are required for 20 mph then ask it to read Dft Circular 01/2006 a little more carefully.

For further details email rodk@20splentyforus.org.uk or call Rod King on 07973 639781 or Chris Mayes on 0151 706 4464