M4 junctions 3-12

We’ve made improvements on the M4 between junctions 3 and 12 by adding an additional lane for traffic to help increase capacity and reduce congestion. We’ve also put in place new technology to smooth traffic flows and manage incidents along this stretch.

Start date 2018

End date 2022

Cost £848 million

Weekend closure: the M4 will be closed westbound between junctions 6 and 8/9 (Holyport Interchange) from 9pm on Friday 13 until 12pm on Sunday 15 October 2023. Diversion via A355, A332, A308 and A308(M).

Latest updates

06 October 2023

Weekend closure

The M4 will be closed westbound between junctions 6 and 8/9 from 9pm on Friday 13 until 12pm (midday) on Sunday 15 October 2023.

A fully signed diversion will be in place via A355, A332, A308 and the A308(M).

This is so we can safely carry out essential bridge joint repairs, surfacing, and waterproofing on the Thames Bray bridge.
05 December 2022
Upgraded motorway between junctions 3 and 8/9 now open

The national speed limit has been restored between junctions 4 and 8/9. This marks the lifting of the final restriction on the upgraded M4 between junctions 4 and 12.

A section between junctions 3 and 4 in West London will remain at 60mph to help manage air quality in the area, and to manage traffic into London; our upgrade of the road and calibration of the technology here is complete.

You’ll have seen between junctions 3 and 8/9 all lanes of the upgraded carriageway were open and the speed limit was 60mph. Drivers were kept at a lower maximum speed limit while we adjusted the technology which detects stopped vehicles. We have now increased the maximum speed on the upgraded section but we continue to make small adjustment to the technology and routinely check the system.

If drivers get into difficulty between junctions 3 and 8/9, they will be able to use one of 16 new emergency areas, bringing the total of emergency areas on the M4 between junctions 3 and 12 to 34. In total there are 59 places to stop in an emergency, including retained sections of hard shoulder between junctions and on junction slip roads, every 1.3 miles on average.

We use a system of inter-related features and technology on upgraded motorways which 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 which provide drivers with information that alerts 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 
Some lane and slip road closures will take place overnight for the next few weeks while we remove temporary traffic management associated equipment.

This is 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. We would like to thank you for your co-operation and understanding during this phase and during the roadworks that we started in 2018.

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 ‘Driving on motorways’ hub.
01 December 2022

Weekend closure as M4 upgrade reaches final stages

Road users are advised that a section of the M4 in Berkshire between Slough and Maidenhead will be closed as a major upgrade reaches its final stages.

The road will be closed between junction 6 (Slough) and junction 8/9 (Maidenhead) from around 10pm Friday 2 December and reopen by 6am on Monday 5 December 2022 while work is carried out on the Thames Bray bridge and various other finishing works on this section of the upgrade.

Traffic will be diverted onto the A308M, the A308, the A332 & the A355. 

Variable speed limits introduced earlier this year will continue to operate on the M4, with some sections starting to return to the national speed limit. A new camera system is now fully operational, in addition to supplementary traffic officer patrols which will continue to monitor the road while we decommission the temporary CCTV and free recovery service.

The M4 upgrade is expected to fully open in the next few days.
18 November 2022

Update on our work between junctions 3 and 8/9

We’ve upgraded the M4 between junctions 3 and 12 and thousands of drivers will now benefit from an extra lane and more technology. The measures will also help reduce congestion, support economic growth within the region and make journey times more reliable.

You may be wondering why you’re still driving at 60mph between junctions 3 and 8/9. Safety is our top priority, and we open all of our motorway upgrades in a phased way to help ensure that the technology is fully tested and operational before it goes live.

This includes calibrating the technology that spots stopped vehicles. This might not be as visible as construction activity, but it’s still very important.

During this testing and calibration stage, the new technology is 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.

There is no defined timescale for this phase of commissioning. Safety is our top priority, so we will not rush these essential preparations.

The M4 is operating with all lanes open and we ask drivers to bear us while we continue to calibrate the technology.

We still have the temporary CCTV cameras used for the roadworks, alongside the permanent cameras installed as part of the upgrade, and our free recovery service for anybody who may break down, in place during this calibration phase of the technology.

And if you do get into trouble, there are 16 new emergency areas open between junctions 3 and 8/9, bringing the total number of emergency areas on the M4 between junctions 3 and 12 to 34. Just look for the orange surfacing, pull in and use the phone to call us.

When the upgrade is complete the national speed limit will be restored from junction 4. A 60mph maximum speed limit will remain in place in both directions between junctions 3 and 4 for the foreseeable future to help improve air quality and to manage traffic heading into London.

Weekend closures during November and December 2022

Please be aware that Transport for London are carrying out roadworks between Junctions 1 and 3 of the M4 over the next few months. This work involves lane closures and overnight and weekend closures. Please check the TfL website before you travel.

We'll be closing the M4 in both directions between junctions 3 (Hayes) and 4b (M25) from Friday 18 to Monday 21 November. The closure will start after 10pm Friday 18 November and the motorway will reopen by 6am on Monday 21 November 2022. Traffic will be diverted onto the A312, A40, M40 and the M25.

We'll be closing the M4 in both directions between junctions 4b (M25) and 5 (Langley) from Friday 25 to Sunday 27 November. The closure will start from approximately 10pm Friday 25 November and the motorway will reopen by 6am on Sunday 27 November 2022. Traffic will be diverted via the A4, A3044 & A3113.

We'll be closing the M4 in both directions between junctions 6 (Slough-Windsor) and 8/9 (Maidenhead) from Friday 2 to Monday 5 December. The closure will start from approximately 10pm Friday 2 December and the motorway will reopen by 6am on Monday 5 December 2022. Traffic will be diverted onto the A308M, the A308, the A332 & the A355.
06 July 2022
Upgrade moves into testing phase between junctions 3 and 8/9

Since the 17-mile section between junctions 8/9 at Maidenhead and 12, for Theale, was opened in December 2021, we’ve been continuing with our work on the 15-mile eastern section, between junctions 3 at Hayes and 8/9.

This week will see us start our phased opening between junctions 3 and 8/9. You’ll notice cones and barriers starting to be removed overnight on 6 July, with all lanes becoming open to traffic. Due to the length of traffic management to remove, it will take us several nights. All cones will be lifted on this stretch by 6am on 16 July.

Once all lanes are open, the motorway speed limit will be increased to 60mph while we calibrate the newly-installed technology. This means it will 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.

Upcoming weekend closures:
- The M4 and associated slip roads will be closed westbound between junctions 11 (Reading) and 12 (Theale). The closure will start after 8pm Friday 23 September and the motorway will reopen by 6am on Monday 26 September 2022. Clearly signed diversions will be in place utilising the A4 and A33.
- The M4 and associated slip roads will be closed eastbound between junctions 12 (Theale) and 11 (Reading). The closure will start after 8pm Friday 30 September and the motorway will reopen by 6am on Monday 3 October 2022. Clearly signed diversions will be in place utilising the A4 and A33.
- The M4 and associated slip roads will be closed eastbound between junctions 11 (Reading) and 10 (Wokingham). The closure will start after 8pm Friday 7 October and the motorway will reopen by 6am on Monday 10 October 2022. Clearly signed diversions will be in place utilising the B3270, A3290 & the A329M.
- The M4 and associated slip roads will be closed eastbound between junctions 11 (Reading) and 10 (Wokingham). The closure will start after 8pm Friday 14 October and the motorway will reopen by 6am on Monday 17 October 2022. Clearly signed diversions will be in place utilising the B3270, A3290 & the A329M.
In the event of poor weather conditions or other issues out of our control, planned work may be postponed at short notice. Contingency bookings are also in place, but these are only used if previously planned work is delayed and there is no clash with other closures. If work completes on an earlier day the motorway may not close, or if work completes ahead of schedule the motorway may reopen early. Signage will be in place on the network to notify of closures and diversions.
24 May 2022

Update on our work between junctions 3 and 8/9

Since the 17-mile section between junctions 8/9 at Maidenhead and 12, for Theale, was opened in December 2021, we’ve been continuing with our work on the 15-mile eastern section, between junctions 3 at Hayes and 8/9.

Construction on this stretch will be largely complete by the end of spring, and we’re aiming to begin the phased opening in summer 2022, with all lanes open at 60mph.

During the next phase, the technology will be calibrated. This means it will 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.

Dedicated monitoring of temporary CCTV in the roadworks and free recovery will be in place.

Once the system is performing to an acceptable level at 60mph, the maximum speed will be increased to the national speed limit. It is important to note that from this point onwards further calibration continues as we go through a process of continual improvement.

This will be the final section of this major motorway upgrade to open, and we are looking forward to real improvements it will bring to more than 130,000 journeys every day

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. 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 ‘Driving on motorways’ hub.
02 February 2022
Work between Junctions 8/9 and 12 complete

All temporary restrictions have now been removed and our upgrade of the M4 motorway between junctions 8/9 and 12 is finished.

The key changes you will see are as follows:
- You will be able to drive between junctions 8/9 and 12 at the national speed limit.
- There will be variable speed limits at certain times to smooth out traffic and tackle frustrating stop-start congestion.
- The hard shoulder has been converted to a new fourth traffic lane in each direction, boosting capacity by a third on this vital route between London, the south west and Wales.
- If you get into difficulty, you are able to use one of 29 places to stop in an emergency which include emergency areas.
The new radar Stopped Vehicle Detection (SVD) system identifies a stopped vehicle, typically within 20 seconds, and provides an alert to our control room. At the same time, it can also automatically display a ‘report of obstruction’ message to warn oncoming drivers of a stopped vehicle ahead. Our operators then set a Red X sign to close one or more lanes, adjust speed limits and deploy traffic officers.

When the entire upgrade project between junction 3 and 12 is fully completed, there will be places to stop in an emergency approximately every 1.3 miles.

We are grateful for your patience while we’ve been carrying out this work.

Construction is continuing between junctions 8/9 and 3.

Our video explains more about the features that work to help keep you safe while driving on this upgraded section of the M4. You can also find more information and advice on our ‘Driving on motorways’ hub.

Planned weekend closures for May 2022

14 - 16 May 2022 – weekend overnight closures between junctions 5 and 6

The M4 will be closed overnight in both directions over the weekend of 14 - 16 May 2022 between Junctions 5 (Langley) and 6 (Slough-Windsor). The closures will start at 10pm on Saturday and Sunday evening, reopening by 6am the next morning.

20 - 23 May 2022 – full weekend closure between junctions 6 and 8/9

The M4 will be closed in both directions over the weekend of 20 - 23 May 2022 between Junctions 6 (Slough-Windsor) and 8/9 (Maidenhead). The closure will start at 10pm Friday 20 May and the motorway will reopen by 6am Monday 23 May.

Our news bulletins gives more information about the project and there will be further updates on this page. Please check before you travel.
16 June 2020

Project reaches halfway point

In June 2020 the project hit the halfway point with the work to extend the New Thames Bridge at Bray that carries the M4 over the river. This bridge - started in 1937, delayed by World War II, and completed as part of the new M4 motorway that opened in 1961 – is being widened on the north side by 8 metres to accommodate the extra lanes required for the new smart motorway.

We are continuing our steady progress on the western section between junctions 8 and 9 to junction 12 which started in July 2018. We expect to finish most of the work on this section by the latter part of 2020, before opening it as a smart motorway during 2021. The eastern section is more complex due to a significant amount of bridge work and will open in 2022.

We are following Government policy which is that construction activity should continue where it can be done safely. All our sites have strict safeguarding measures to prevent the spread of COVID-19 and none of our sites are open to the public. With traffic volumes on our roads still lower than usual, we are continuing to work before traffic flows eventually return to normal. We plan our work carefully in order to minimise travel disruption.

See more updates

Project information

Visit our M4 J3-12 feedback tool to have your say. The tool includes an interactive map. You can click on a location to make a specific comment, or give us your general feedback.

ECHO is a one-way feedback tool, so if you’d like a response to your feedback you can email the project team at: M4J3to12smartmotorways@nationalhighways.co.uk

Once our work is completed this stretch of the M4 will use the latest technology to monitor traffic flow and set speed limits. This will help keep traffic moving smoothly, instead of continually stopping and starting.

Between junctions 3 and 12 the hard shoulder will be converted to a traffic lane, so there will be four lanes available for use by road users. Between junctions 4 and 4b, there will be five lanes. There will also be five lanes on the eastbound approach to Junction 4b.

Where a hard shoulder does not currently exist, the motorway will be adapted to create a minimum of four lanes, including under the 11 bridges which are being replaced as part of the project. The barrier in the central reservation will be replaced by a new concrete barrier.

The M4 is the main strategic route between London, the West of England and Wales. It connects people, communities and businesses, carrying on average 130,000 vehicles per day.

The changes we’re making will:

reduce congestion
smooth the flow of traffic to improve journey times
make journeys more reliable
support economic growth within the region, by providing much needed capacity on the motorway
continue to deliver a high level of safety performance on the network using smart motorway techniques and minimise environmental impacts of the scheme

Statutory Instrument Consultation

Secretary of State decision

Development Consent Order

Speed limit consultation

Pre-application consultation

The DCO process was established by the Planning Act 2008 and is used for certain large and complex schemes (including highway improvements) that have been designated as a Nationally Significant Infrastructure Project (NSIP) by the Government.

The benefits of the DCO process include extensive pre-application consultation, detailed analysis, including a full Environmental Impact Assessment, and examination by an independent inspector before the final decision is made.

Development Consent Order – requirements register

We made a commitment to publish and update a register listing the requirements to be completed as part of the Development Consent Order (specified under the Register of Requirements in Schedule 2). This sets out:

each requirement
whether the requirement needs approval by the Secretary of State (or other duty holder)
whether any approval has been applied for or given

All of the DCO requirements needed to start work were discharged in summer 2018.

Since the Development Consent Order (DCO) for the project was granted in 2016, there have been some changes to the design and we’ve submitted an application to change the DCO. The following changes are included in the application:

No-Through Junction Running (No-TJR) is proposed at Junctions 5, 6, 8/9 and 11 where previously Through Junction Running (TJR) had been proposed;
three new bridges (Huntercombe Spur, Oldway Lane and Wood Lane) where the height is outside of the limits provided for by the DCO;
The widening of Sipson Road Subway to the north due to site constraints, instead of the previously proposed widening to the south;
To facilitate the detailed design of the scheme where details are not consistent with those set out in the Engineering Design report submitted with the DCO in 2015 and previously approved. This includes changes such as to the number of spans, footway locations and extensions to culverts; and:
Changes to acoustic barriers in the Wokingham area.

Full details including a copy of the application documents, plans and maps showing the nature and location of the changes are available to be viewed and downloaded for inspection, free of charge, at the National Infrastructure Planning Portal.

Full details on how to respond are also available on the National Infrastructure Planning Portal. Any comments or representations on the Application must be received no later than 11.59pm on 03 June 2022.