Progress of the M4 junctions 3 to 12 motorway upgrade project. From National Highways

Published: 08 July 2022

Once all lanes are open, the motorway speed limit will be increased to 60mph while we calibrate the newly-installed technology. This means it’ll be finely adjusted to suit the particular environment of the road where it has been installed. This can only happen when there are no roadworks, and when drivers are able to use all lanes of the upgraded carriageway. As a safety measure the maximum speed limit is set at 60mph.

All motorways, with or without a hard shoulder, are designed and operated with drivers centrally in mind, to be easy and straightforward to drive on. The technology currently used on smart motorways, all focussed on drivers, is a system of inter-related features creating a layering effect. These include:

· Variable speed limits to help keep traffic moving, reducing frustrating stop-start traffic and making journeys quicker 

· Clearly signed and orange-coloured emergency areas set back from the road and with telephones linking directly to our control rooms 

· Detection systems to monitor traffic for changes in flows 

· Stopped Vehicle Detection (SVD) technology which can identify a stationary vehicle, typically within 20 seconds

· CCTV cameras that our operators are able to move and zoom to monitor and manage congestion and incidents, where notified. The system has the ability to see 100% of the carriageway Signs and signals to provide information to drivers which can alert them to hazards ahead

· Red X signals to close lanes to other traffic when a stopped vehicle is identified 

· Enforcement cameras to deter the minority who break speed limits and ignore Red X signals 

During the calibration phase, we maintain the temporary CCTV cameras used for the roadworks, alongside the permanent cameras installed as part of the upgrade. We’ll also maintain our free recovery service for anybody who may break down during this calibration phase of the technology.

The newly opened section will include 16 new emergency areas, bringing the total of emergency areas on the M4 between junctions 3 and 12 to 34, with a place to stop in an emergency every 1.3 miles on average.

Once the system is performing to an acceptable level at 60mph the maximum speed will be increased to the national speed limit. Routine operational checks of the system will continue.

This will be the final section of this major upgrade to open on one of the busiest stretches of motorway in the country. We’re looking forward to real improvements it will bring to more than 130,000 journeys every day.

If you’d like to know more about the main features of smart motorways, and advice and guidance on safer driving and what to do in an emergency, visit our new ‘Driving on motorways’ hub:

Transport Select Committee

We’ve listened to public concerns about smart motorways, and we are fully committed to taking forward the additional measures the Transport Select Committee has recommended. We’re doing this because safety is our absolute priority and we want drivers to not just be as safe as possible, but also to feel safe on our network.

You can read more about how we’re delivering the recommendations from the Transport Select Committee’s on our website:

We are grateful for your patience whilst we have carried out this work. You can continue to check the website for any further updates at:

Please note that maintenance of the motorway network takes place on a regular basis so you may still see occasional closures from time to time.

If you have any further queries or require any information, please contact us on the details below or visit the National Highways website.

Kind regards

Anu Vashisht, Administrator (Smart Motorways Programme)
National Highways | 2 Colmore Square | Birmingham | B4 6BN
Tel: 0300 123 5000 (Customer Contact Centre)