Wales has become the first country in the UK to introduce a standard 20mph speed limit on residential roads.
The program begins on Sunday and most roads in Wales currently traveling at 30mph have moved to 20mph, although councils have the discretion to impose exemptions.
The Welsh Government has said reducing speeds from 30 to 20mph will protect lives and save the NHS in Wales £92 million a year.
The RAC warned motorists not to rely on sat-navs for the correct speed limit and instead follow road signs.
But any motorist caught driving at more than 20mph but less than 30mph will first be given advice by police rather than face a ticket, a minister said.
Lee Waters, deputy minister for climate change, told the PA news agency: “Initially it’s all about educating people and talking to them, not about issuing fines, but over 30mph we will be issuing fines and Give points.”
The minister said he expected it would take about a month for motorists to get used to the changes, but said trials of the 20mph limits would cause a typical delay of one to two minutes on an average journey would have shown.
“Most delays are not due to speed but could be due to delays at intersections and traffic lights,” he said.
“We’ve all been overtaken by an idiot, only for him to find a spot ahead of us at the traffic lights.
“A business model that assumes that someone is taking a dangerous path is not a very good business model.”
Councils have the power to change the standard speed limit on any local road, but Mr Waters said some local authorities were strictly following Welsh Government guidelines.
“The risk appetite of municipalities varies significantly,” he said.
“For example, Vale of Glamorgan and Rhonda Cynon Taff have introduced a whole range of exemptions and exempted thoroughfares.
“Other councils have not done this and they are afraid to deviate from the letter of the guidance.
“But I think confidence will grow and experience will influence that and I think if you give it a year or two then it will calm down.”
The project will cost around £33 million to implement and has proven controversial. The new 20mph signs have reportedly been defaced in areas including Conwy, Gwynedd, Newport, Torfaen, Wrexham and Flintshire.
The Welsh Conservatives opposed the plan and tabled a motion in the Senedd to stop the rollout, but were defeated.
They cited Welsh Government documents estimating the cost to the Welsh economy of longer journey times due to lower average speeds at between £2.7 billion and £8.9 billion.
They want more “targeted measures” than the introduction of the standard speed limit with exceptions and compare this to the Ultra Low Emission Zone (Ulez) in London.
Andrew RT Davies, leader of the Conservatives in the Senedd, said: “Whilst I agree that 20mph outside busy areas such as schools, hospitals and care homes makes sense, the blanket speed limit of 20mph across Wales is Labor’s -Government simply ridiculous.” .”
Natasha Asghar, the Welsh Conservatives’ shadow transport minister, added: “Labour and Plaid Cymru have refused to listen to public opinion and continue to pursue their anti-worker, anti-road and anti-driver agenda.”
But organizations including Brake, Cardiff Cycling Campaign, We Are Cycling UK Cymru, Friends Of The Earth Cymru, Sustrans and Living Streets Cymru have signed a joint letter organized by the 20’s Plenty For Us campaign supporting the rollout.
“It’s not just a benefit for road safety. It also supports broader health, climate and societal goals, such as: “Such as helping vulnerable people get around, improving social connections, reducing air and noise pollution and more,” they said.