M4 junctions 3-12: smart motorway

We’re improving the M4 between junction 3 at Hayes and junction 12 at Theale by upgrading it to a smart motorway. This means there will be an additional lane for traffic which will increase capacity and reduce congestion, more technology on the road to smooth traffic flows and manage incidents and more reliable journey times.

Start date 2018
End date 2022
Cost £848 million

Latest updates

  • 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.

Project information

Give us your feedback

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

M4 J3-J12 feedback tool

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

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:

  1. 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;

  2. three new bridges (Huntercombe Spur, Oldway Lane and Wood Lane) where the height is outside of the limits provided for by the DCO;

  3. The widening of Sipson Road Subway to the north due to site constraints, instead of the previously proposed widening to the south;

  4. 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:

  5. 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.  

Documents

Newsletters

M4 junctions 3 to 12 upgrade - Newsletter March 2022
M4 junctions 3 to 12 upgrade - Newsletter December 2021
M4 junctions 3 to 12 upgrade - Newsletter October 2021
M4 junctions 3 to 12 upgrade - Newsletter August 2021
M4 junctions 3 to 12 upgrade - Newsletter July 2021
M4 junctions 3 to 12 upgrade - Newsletter June 2021
M4 junctions 3 to 12 upgrade - Newsletter May 2021
M4 junctions 3 to 12 upgrade - Newsletter April 2021
M4 junctions 3 to 12 upgrade - Newsletter March 2021
M4 junctions 3 to 12 upgrade - Newsletter February 2021
M4 junctions 3 to 12 upgrade - Newsletter January 2021
M4 junctions 3 to 12 upgrade - Newsletter December 2020
M4 junctions 3 to 12 upgrade - Newsletter November 2020
M4 junctions 3 to 12 upgrade - Newsletter October 2020
M4 junctions 3 to 12 upgrade - Newsletter - September 2020
M4 Junctions 3 to 12 upgrade - Newsletter - August 2020
M4 junctions 3 to 12 upgrade - Newsletter July 2020
M4 junctions 3 to 12 upgrade - Newsletter June 2020
M4 junctions 3 to 12 upgrade - Newsletter May 2020
M4 junctions 3 to 12 upgrade - Newsletter April 2020
M4 junctions 3 to 12 upgrade - Newsletter March 2020
M4 junctions 3 to 12 upgrade - Newsletter February 2020
M4 Junctions 3 to 12 upgrade - Newsletter - January 2020
M4 Junctions 3 to 12 upgrade - Newsletter - December 2019
M4 Junctions 3 to 12 upgrade - Newsletter - November 2019
M4 Junctions 3 to 12 upgrade - Newsletter - October 2019
M4 Junctions 3 to 12 upgrade - Newsletter - September 2019
M4 Junctions 3 to 12 upgrade - Newsletter - Summer 2019
M4 Junctions 3 to 12 upgrade - Newsletter - June 2019
M4 Junctions 3 to 12 upgrade - Newsletter - May 2019
M4 Junctions 3 to 12 upgrade - Newsletter - April 2019
M4 Junctions 3 to 12 upgrade - Newsletter - March 2019
M4 Junctions 3 to 12 upgrade - Newsletter - February 2019
M4 Junctions 3 to 12 upgrade - Newsletter - January 2019
M4 Junctions 3 to 12 upgrade - Newsletter - December 2018
M4 Junctions 3 to 12 upgrade - Newsletter - November 2018
M4 Junctions 3 to 12 upgrade - Newsletter - October 2018
M4 Junctions 3 to 12 upgrade - Newsletter - September 2018
M4 Junctions 3 to 12 upgrade - Newsletter - July 2018

Traffic information

Information about scheduled roadworks and events on our motorways and major roads.

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