Let me be absolutely clear, I am totally in favour of the 20mph speed limit changes coming into law four weeks from now.

The case in favour of them is crystal clear. Thousands, yes thousands of casualties saved each year, many of them to children. Injuries prevented; lives saved.

And the advantages do not stop there: the evidence shows the new limit will deliver benefits to air quality, active travel, noise pollution, greater social inclusion, greater community cohesion and local business viability.

I am delighted that Wales is leading the way on this. Make no mistake, others will follow.

The evidence is so clear. Don’t just take my word for it. Independent research confirms the advantages. Two thirds of people in South East Wales are already welcoming the changes, only one in seven say they can see little advantage, more than half want motorists to slow down in urban areas.

And what is the downside? Seconds more on local journeys. Travelling a full mile at 20mph takes just one minute longer than it does at 30mph. To be frank, if you have a journey where every second counts, you may not be the safest motorist on the road in the first place!

In fact, it all reminds me of the initial reluctance to make seat belts compulsory. There were the doubters and the anti-brigade back then, too.

I accept that there may be a few wobbles along the way in terms of implementation. While the benefits for most urban streets are clear, its less easy to get it right where roads going through villages and towns have become fast commuter routes. 

After the first pilots last year, we decided to work through the possible exceptions on a road-by-road basis with local county councillors. We need to get the signage right, and to communicate the arguments for lower speed limits better. 

We are also aware of the concerns about cost–but in the whole of Wales the cost of making the changes in the first year alone will be dwarfed by the savings, estimated to be three times higher.

But this is not about money. It is about public good. Balancing the needs of the motorist against the benefits to society as a whole. It is a small adjustment to make. An important and positive one.