The Welsh Government has continually touted the benefits revealed in a health study which found the 20mph speed limits could result in 40 per cent fewer collisions and save thousands of people from being injured every year.
Legislation has also been introduced to encourage more people to walk or cycle, as well as reduce noise pollution.
The introduction of the changes is expected to cost £32million, although the savings for the NHS could be up to £92million every year.
Lee Waters, deputy minister for climate change in the Welsh Government, said he expected it would take drivers around a month to adjust to the speed limit changes.
The Labour MS for Llanelli added: “Very much the intention initially is to educate and to speak to people and not to fine but over 30mph we will be fining and issuing points.
“Most delay doesn’t occur because of speed, it could be because of delays at junctions and traffic lights. We’ve all been overtaken by an idiot only to find them one space in front of us at the lights.
“A business model that makes assumptions about somebody driving in a way that is dangerous is not a very good business model,” he told the PA news agency.
However, Natasha Asghar, the Welsh Conservative shadow transport minister, slammed the plans and took aim at the decision to go ahead with the law changes.