20mph Zones and Limits
“Research shows that reducing speed on the roads dramatically reduces the severity of collisions and encourages more people to walk. There are approximately 560 20mph speed limits and zones in Wales, many of which have been funded by the Welsh Government”.
There are two distinct types of 20mph areas possible:
20mph zones, are designed to be "self-enforcing" by installation of traffic calming measures which are introduced along with the change in the speed limit. Speed humps, chicanes, road narrowing, planting and other measures are typically used to both physically and visually reinforce the shared nature of the road.
20mph limits, which consist of a speed limit change but no physical measures to reduce vehicle speeds within the areas. Drivers are alerted to the speed limit with 20mph speed limit repeater signs.
20mph limits are most appropriate for roads where average speeds are already low, and the guidance suggests below 24mph. The layout and use of the road must also give the clear impression that a 20mph speed or below is the most appropriate.
As well as road safety benefits, it is important to highlight the contribution that 20mph zones can have in encouraging more physical activity, such as walking and cycling, by contributing towards a safer environment. The money spent on the schemes can also greatly improve the character of a residential area and quality of life of the residents.
GoSafe and 20mph areas
GoSafe have long advocated compliance with speed limits in order to contribute to safer roads: speed is often an aggravating factor in frequency and/or severity of collisions. We support our communities by enforcing at sites of concern which evidence lack of compliance with the speed limit. GoSafe welcomes the development of a national speed awareness course which will contribute to the awareness of drivers exceeding the speed limit through 20mph areas.
 Source: http://www.rospa.com/roadsafety/adviceandinformation/highway/20-mph-zones.aspx