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Rydym yn croesawu galwadau’n Gymraeg | We welcome calls in Welsh

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The Welsh Government’s traffic information service for motorways and trunk roads in Wales

M4 J24-28 50mph Average Speed Enforcement Scheme FAQs

This scheme uses technology to tackle congestion on a 13km stretch from junction 24 (Coldra) to junction 28 (Tredegar Park).

Approximately 120,000 vehicles travel this busy stretch of the M4 each day. This project is crucial to improve driver safety, traffic flows and road users' experience. It is expected that replacing the variable speed limit with an average speed enforcement system will:-

·        help manage on-going congestion issues along this stretch of the M4.

·        improve journey time reliability during peak times and provide smoother traffic flows.

·        reduce the risk of collision.

·        provide better air quality as toxic emission levels are reduced.


This forms part of the Welsh Government’s approach to tackling congestion in the area as recommended by Lord Burns’ report published following the work carried out by the South East Wales Traffic Commission.

Their traffic flow data shows that late lane changes and variable traffic speeds often lead to breakdown of flow on the M4 around Newport, especially on the approaches to the Brynglas tunnels. Although the VSL system has been effective at regularising speeds during the inter-peak period, it has had a limited impact on improving traffic flow during peak periods.

Their analysis suggests an average speed control would help improve the regularity of traffic speeds across the problematic stretches of the M4

The permanent 50mph limit between junctions 24 and 28 on the M4 will be enforced from 17/11/22. Notices of prosecution will then begin to be issued.

The cameras will be operational and the mandatory 50mph speed limit will be monitored closely by Go Safe during the bedding-in period. It will allow for full systems and enforcement checks to take place and give motorists time to get used to the new speed limit. Notices of prosecution will then begin to be issued in the Summer.

In certain circumstances, lower advisory speed limits may also be set manually by control centre operators or triggered by the queue protection system. The reason is usually to support maintenance works and help protect the workforce, especially when completing the dangerous job of setting out and removing traffic cones. Occasionally, particularly at night, it can appear that speed limits have been set for no reason but this may be because drivers are seeing the signs just before the cones are set out or just after they have been removed.

The carriageway surface has been renewed and additional lane destination markings have been provided to promote lane discipline. Advanced road markings in combination with the current signs will help to prevent late lane changes and will mean that road users will be given as much notice as possible to use the correct lanes.

Welsh Government Traffic Officer recruitment has been increased. This will enable us to improve response times and extend patrols on the A48 and A4810 in Newport to help manage traffic in this area.

Average Speed Limit enforcement - managed by GoSafe

The average speed control system will measure the average speed over a road section. The vehicle is identified when entering the enforcement section, and again when leaving it. The system has the necessary Home Office Type Approval (HOTA) which allows its use for enforcement purposes.

Speed enforcement through the use of roadside cameras across Wales is managed and coordinated by GoSafe, a multi-agency partnership comprising all highway authorities within Wales and the four Welsh police forces. Within that partnership structure the Welsh Government owns and installs the cameras located on the M4 motorway and the police, as the enforcement authority, are responsible for operating them and carrying out enforcement on a day-to-day basis.

There are built-in safeguards which prevent cameras from activating if there is a technical fault. The system is designed to ensure that it will only capture an offence when the equipment is working correctly. This is a requirement of HOTA.

The cameras are mounted on overhead gantries and roadside structures and enforcement is carried out by the police. The scheme is capable of enforcing 24 hours a day, 7 days a week and is set up to account for people joining or leaving the M4 at junctions between junctions 24 and 28. More information on camera locations and enforcement can be found at

Call the Traffic Wales information line
0300 123 1213

Rydym yn croesawu galwadau’n Gymraeg
We welcome calls in Welsh

Contact us