To ask the Secretary of State for Northern Ireland on which roads in Northern Ireland a 20 mile per hour speed limit is imposed; and what assessment he has made of the effect on road safety at each location of such a limit. (129587)

The Chief Executive of Roads Service (Dr. Malcolm McKibbin) has been asked to write to the hon. Lady in response to this question.

Letter from Dr. McKibbin, dated 3 April 2007:

You recently asked the Secretary of State for Northern Ireland a Parliamentary Question regarding, on which roads in Northern Ireland a 20 mile per hour speed limit is imposed; and what assessment he has made of the effect on road safety at each location of such a limit.

As this issue falls within my responsibility as Chief Executive of Roads Service, I have been asked to reply.

By way of background, I should explain that a 20 mph speed limit is not normally introduced on individual roads. It is more common to introduce 20 mph zones, which are a form of traffic calming in residential areas where an extensive network of streets is involved and where self-enforcing measures can be provided to reduce vehicle speeds to approximately 20mph. Where speeds have been reduced to 20 mph by self-enforcing measures, it is then possible to introduce a mandatory 20 mph limit. However, if the level of traffic calming measures is insufficient to reduce speeds to around 20 mph, then it is unlikely that the Police Service of Northern Ireland would agree to the introduction of a mandatory 20 mph limit.

Roads Service has implemented forty-eight 20 mph residential zones, the locations of which are listed in the following table. In addition, Roads Service is currently progressing a 20 mph zone for the Scrabo Estate, in Newtownards, through the approval stage.

Roads Service currently monitors the effectiveness of all traffic calming schemes, including 20 mph zones, and this information is published in our annual Road Safety Engineering Report, a copy of which can be obtained from our website at: http://www.roadsni.gov.uk/Publications/specific/RoadSafetyEngReport0405-0506.pdf or by writing to Mr Brian Maxwell, Network Traffic Telematics Manager, Traffic Information and Control Centre, 1b Airport Road, Belfast, BT3 9DY. For each scheme, the number of injury collisions occurring over the three year period following introduction of a scheme, is compared with the collision history for a similar period prior to the works.

At fourteen of the above forty-eight locations, where full monitoring data is available, there have been 88 fewer collisions involving an injury. This equates to a 32% reduction compared with a similar period before introduction of the 20 mph zones.