New 20mph limits are helping cut speeds and will save lives, the Welsh Government has insisted.

Drivers are travelling on average 4mph slower on main roads in Wales since the rollout of a new lower speed limit for built-up areas, data collected by Transport for Wales (TfW) shows.

The Welsh Labour Government, which implemented the change in September last year, insists the lower speeds will lead to fewer collisions and people injured.

But the change has seen fierce opposition from the Conservatives in the Senedd, who have branded it a “waste of time and resources”.

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The TfW data shows that average speeds have dropped from 28.9mph to 24.8mph since the measure was put in place.

Research undertaken by the Transport Research Laboratory, a transport consultancy, in 2000 suggested there is an average 6% reduction in collisions with each 1mph reduction in average speed on urban roads.

Lee Waters MS, the deputy minister for climate change, said: “The latest data published today is clear evidence that average speeds are coming down on roads across Wales.

“We also know from data published by Go Safe earlier this month that 97% of drivers are complying with the new slower speed limit – behaviours and attitudes towards 20mph are beginning to change.

“We’ve still got a way to go, but it’s encouraging to see that things are moving in the right direction. Every 1mph reduction in speed makes a real difference – so this is a real turning point.”

Mr Waters added that evidence was clear that lower speeds would help save lives, lead to fewer injuries and reduce the impact on the NHS.

Ross Moorlock, chief executive of the road charity Brake, said the reduced speed was “encouraging” and called on the UK Government to follow Wales’ lead.

He said: “Every day, five people die on UK roads and speed is a factor in every crash. The faster we drive, the greater our risk of crashing, and the harder we hit if we do crash.

“We know that road crashes have a devastating impact on families and communities.”

Natasha Asghar MS, the Welsh Conservative shadow minister for transport, said: “These findings prove what a monumental waste of time and resources from the Labour Government the 20mph limit has been.

“To sacrifice billions of pounds from the Welsh economy all for the sake of 4mph may satisfy Labour, but it is not a trade the Welsh Conservatives would be willing to make.

“On day one of a Welsh Conservative Government, this barmy policy would be scrapped, and common sense would prevail.”

A petition against the roll-out of the law, on the Welsh Parliament’s petitions page, has now been signed by almost 469,000.