The 50mph limits were introduced as a trial in December 2018 on the M4 near Port Talbot
Speed cameras to enforce 50mph limits designed at improving air quality on the M4 and other roads have been activated.
The limits were put in place as a trial in December on the M4 near Port Talbot and roads through Pontypridd, Wrexham and Deeside.
They have now been made permanent and became operational in September.
The Welsh Government said the cameras would help deliver “vital improvements in air quality”.
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The cameras have been placed on the M4 near Port Talbot, the A470 at Upper Boat, the A483 in Wrexham and A494 in Deeside.
Some equipment on the M4 was removed following a “technical issue” but has been reinstalled.
The High Court had ordered ministers to act after they failed to meet EU targets on air pollution.
The Welsh government confirmed in June the restrictions would be permanent, saying nitrogen dioxide levels were above legal limits and “must be reduced”.
In January 2018, the Welsh government conceded a case brought by environmental campaign group Client Earth which said ministers had failed to meet EU targets to cut pollution.
Client Earth campaigns and policy manager Andrea Lee urged the government to do everything possible to meet air pollution legal limits quickly.
Paul Biggs, environment spokesman for the Alliance of British Drivers (ABD), said: “Speed cameras wouldn’t be necessary if speed limits weren’t set at an inappropriately low 50mph.
“The air pollution excuse is simply unfounded scaremongering given that a report by DEFRA shows NOx emissions have fallen by 72% and particulates (PM2.5) by 79% since 1970.
“Longer journey times and increased congestion as a result of these measures won’t reduce vehicle emissions.”