Welsh Labour, the ruling party in Wales, has been working plans to limit residential roads and busy pedestrian streets to 20mph for some time.
The principle aim is that the change will reduce the number of people being killed or seriously injured in road crashes in Wales whilst also helping to limit emissions and protect the environment.
The policy, which has caused severe outrage with many questioning the reasoning behind the implementation will come into force in September 2023.
In a report just released, the Welsh Government's own analysis says that reducing the speed limit from 30mph to 20mph could cost the economy billions.
Though some have applauded the plans the Welsh Government's own analysis points to a potential £4.5bn hit to the economy over a 30-year period.
For context, the Welsh Government's education budget is just over £3bn a year.
Published in the explanatory memorandum on the topic, the minister for climate change signed off on the analysis saying it "gives a fair and reasonable view of the expected impact" of the 20mph limit and that she is "satisfied that the benefits justify the likely costs".
A Welsh Government spokesman said: “Our assessment shows an average increase of one minute per journey, which results in a saving of nine lives and prevents 98 serious injuries annually.”
When asked about the increased cost to the economy by the BBC deputy climate change minister Lee Waters said: "The idea that being a minute later to get to school harms the economy, I just don't believe it, so I think the figures are discredited in my view and there's a movement to change that. Also it's going to save lives - we know it's going to save lives."