Drivers who break the 50mph limits on parts of A470 and other main roads in Wales will be warned and prosecuted from monday.
Cameras have been monitoring the A470 near Pontypridd, A483 south of Wrexham and on the A55 and A494 Deeside since the middle of 2018 but from monday 4 October, the warnings and prosecutions will begin.
The new speed limits were introduced in a bid to cut air pollution and reduce accidents on busy sections of the roads which scientists said posed particular health risks.
The latest camera monitoring technology will also be used to detect drivers using hand-held mobile phones along the stretches and potentially dangerous driving.
Advisers have claimed to Welsh Government that the speed reductions could cut harmful exhaust emissions by up to 18% alongside the roads and are part of a £20M air quality fund from Welsh Government which will encourage the creation of Clean Air Zones in built up areas.
Cardiff plans to restrict access and charge commuters attracted immense opposition when announced three years ago and it was labelled a plan to tax the poorest motorists travelling from the valleys to work in the capital.
Poor public transport links were cited by opponents and the Welsh Government backed Transport for Wales has struggled to keep rail services running efficiently to offer alternatives to private vehicles.
Social distancing restrictions on trains and buses during the current Covid-19 pandemic have added to the issues on public transport and Welsh Government had to bail out the train operators last year when users dramatically stayed off trains and buses, which received grants to keep them operating.
From early October anyone caught exceeding the 50mph limits on the affected roads will get a warning letter within 14 days and a repeat offence will result in a £100 Fixed Penalty Notice and three points on their licence which remain for four years, but newly qualified drivers face having their licence revoked in some circumstances.