All new residential developments containing a road system which measures more than 100m from the entrance of the development to the furthest extremity of the road system are to constitute, or form part of, a 20mph zone.

Speed-restraint measures are to be used throughout 20mph zones and do not require warning signs within the zone. However, signs (in accordance with DfT Traffic Advisory Leaflet 2/93) and an entrance gateway are required to indicate to drivers that they are entering such a zone. While this guidance is intended for developments being designed and constructed in the present, it is worth considering how design measures taken to reduce vehicle speeds could be future proofed, removed or have their space re-allocated if speed-controlled autonomous vehicles become the predominant mode of travel in future.

Speed Restraint designs should not appear 'engineered' or unduly clutter the street scene.  They should instead be subtly incorporated to form an integral part of an attractively designed public realm, including using a coherent (usually simple) palette of materials, colours and textures, and where appropriate exploiting opportunities for increased planting, play and other usable space.  Designs should also respond to the general style of route, for example being formal in nature on regular boulevards but informal where an organic ad-hoc character is desired.

Speed Restraint Within a 20mph Zone

All new residential developments containing a road system which measures more than 100m from the entrance of the development to the furthest extremity of the road system are to constitute, or form part of, a 20mph zone.

To encourage adherence to the designed maximum speed of 20mph, it is necessary to implement one engineering measure drawn from lists (a) or (b) in each 20mph zone. In many circumstances, it will also be necessary to implement a complementary measure drawn from list (c). Lists (a) to (c) can be found in the Speed restraint within a 20mph zone section of the Highways Technical Manual.

Measures to reduce visibility for the driver are not acceptable by themselves. Rumble strips are also not an adequate speed-restraint measure. Speed-restraint measures should be located at maximum intervals of 60m, starting within 50m of the entry junction or zone. They must be in a different surface material from the rest of the carriageway and well-lit. They may take the form of changes in horizontal alignment, changes in vertical alignment or complementary measures.

The visibility of a route can be agreed on a case by case basis, with the standard being applied to the geometry of the road.

In order to qualify for relaxation of signing requirements for speed-restraint measures, each development must receive a Department of Transport Certificate. This should be applied for by the Planning and Highways Authorities after speed checks to confirm that design speeds are being achieved on the completed scheme. However, developers can be reasonably certain that their schemes will comply if the Highway Authority has approved their submitted drawings.