Temporary speed limits of 50mph on the M4 have been made permanent in a bid to cut pollution.
The limits were introduced on the motorway to crack down on air pollution through built-up areas.
The move affects the M4 in Port Talbot and Newport as well as other major roads in Wales, including the A470 Pontypridd, A483 Wrexham and A494 Deeside.
The Welsh Government has confirmed the restrictions are now permanent, reports Wales Online.
A Welsh Government spokesman said nitrogen dioxide levels “must be reduced”.
“It was established that a 50mph speed threshold alone was the measure that would achieve compliance in the shortest time possible,” he said.
“The current speed limit in place will be retained through permanent traffic regulation orders and remain in force to maintain air quality standards.”
The Environment Minister Lesley Griffiths announced the move at plenary, and suggested putting up signs that read ‘poor air quality kills, reduce your speed’.
Ms Griffiths said: “I have been working with the Minister for Economy and Transport [Ken Skates] on actions to address nitrogen dioxide exceedance in five sites across our strategic motorway and trunk road network.
“I am pleased to announce that 50mph speed limits will be in place on a permanent basis across all five sites by the middle of July.
“We will be enhancing communications around the reason for the speed restrictions and providing new permanent traffic sign layouts at all sites, so that the public is aware of the importance of these measures.”
She also addressed concerns that motorists were ignoring the 50mph restrictions.
Speaking about the A483 in Wrexham, Ms Griffiths said: “I’m going along at 50mph and people are overtaking me, I would say, all the time.
“I think one of the areas where I do have concerns – and this will be addressed when we bring the five sites forward on a permanent basis – is that people don’t understand why they are 50mph sites.
“So, I think we need signs saying, ‘poor air quality kills, reduce your speed’.