All residential areas in Wales could become 20mph if the Welsh Government gets its way.
First Minister Mark Drakeford has said that a default speed limit for the whole country should be brought in.
He said deputy transport minister Lee Waters is working with the body which represents councils in Wales, the WLGA, to look at what needs to happen to make 20mph a default limit across Wales.
Supporters of 20mph zones say it improves air quality, reduces accidents and restores a sense of community.
Mr Drakeford made the announcement in the Senedd in response to a question from Conservative AM David Melding.
Councils have power over local speed limits but the Government has control over the national limit.
Mr Drakeford said: “The Welsh Government believe that 20mph should be the default speed limit for residential areas.
“Across this whole Assembly term, my colleague Ken Skates has provided hundreds of millions of pounds for small area 20mph zones.
“What we now want to do is to go beyond that. The city of Cardiff is, I think, a good example of what can be done .
“Local authorities have to have discretion to retain 30mph zones on key arterial routes, but outside that, and in residential areas, we know that 20mph zones reduce speed of traffic, reduce accidents, particularly accidents to children, and we want to see that become the default position right across Wales.
“There are a whole series of advantages including the better air quality that you get through slower traffic speeds.”
Reduced speed zones have already been put in place in areas of Cardiff like Riverside, Canton, Grangetown and Gabalfa as part of the council's actions to improve the safety of Cardiff's roads.
Mr Drakeford said fast-moving traffic moving through a community breaks one part of the community up from another.
“We know that those impacts fall differentially on people, whether it is older people, whether it's children, whether it's people without cars and so on, and so, 20 mph zones allow a reduction in that community severance, and that's another really important social benefit that comes from the policy.”
Campaign group 20s Plenty says a default 20mph speed limit cuts accidents.
In their response to a recent Parliamentary committee, they wrote: “The introduction of 20mph limits in built-up areas has a small but significant impact on vehicle speeds and casualty numbers and when used in combination with other initiatives such as road design, enforcement, new technology and programmes of behaviour change, has the capacity to reduce maximum vehicle speeds towards the 20mph target and thus make major inroads into casualty levels.
“This is an area whose potential for casualty reduction has been largely untapped in recent years.”
There had already been support in Wales from The Institute for Welsh Affairs, Public Health Wales and groups like Living Streets and Brake Wales.
