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

  • 16 March 2021

    Planned weekend closures for March, April and May 2021

    20 March - 22 March 2021 – full weekend closure between junctions 6 and 7

    The M4 will be closed in both directions over the weekend of 20 March – 22 March 2021 between Junctions 6 (Slough) and 7 (Cippenham). The closure will start after 6am Saturday 20 March and the motorway will reopen by 6am on Monday 22 March.

    26 March - 29 March 2021 – full weekend closure between junctions 5 and 6

    The M4 will be closed in both directions over the weekend of 26 March – 29 March 2021 between Junctions 5 (Langley) and 6 (Slough). The closure will start after 8pm Friday 26 March and the motorway will reopen by 6am on Monday 29 March.

    9 April - 12 April 2021 – full weekend closure between junctions 6 and 8/9

    The M4 will be closed in both directions over the weekend of 9 April – 12 April 2021 between Junctions 6 (Slough) and 8/9 (Maidenhead).

    The closure will start after 8pm Friday 9 April and the motorway will reopen by 6am on Monday 12 April.

    16 April – 19 April 2021 – full weekend closure between junctions 5 and 6

    The M4 will be closed in both directions over the weekend of 16 April – 19 April 2021 between Junctions 5 (Langley) and 6 (Slough).

    The closure will start after 8pm Friday 16 April and the motorway will reopen by 6am on Monday 19 April.

    23 April – 26 April 2021 – full weekend closure between junctions 6 and 8/9

    The M4 will be closed in both directions over the weekend of 23 April – 26 April 2021 between Junctions 6 (Slough) and 8/9 (Maidenhead).

    The closure will start after 8pm Friday 23 April and the motorway will reopen by 6am on Monday 26 April.

    7 May – 10 May 2021 – full weekend closure between junctions 6 and 8/9

    The M4 will be closed in both directions over the weekend of 7 May – 10 May 2021 between Junctions 6 (Slough) and 8/9 (Maidenhead).

    The closure will start after 8pm Friday 7 May and the motorway will reopen by 6am on Monday 10 May.

    14 May – 17 May 2021 – full weekend closure between junctions 6 and 8/9

    The M4 will be closed in both directions over the weekend of 14 May – 17 May 2021 between Junctions 6 (Slough) and 8/9 (Maidenhead).

    The closure will start after 8pm Friday 14 May and the motorway will reopen by 6am on Monday 17 May.

    Please check before you travel.

  • 17 February 2021

    Planned weekend closures for February and March 2021

     

    19 February to 22 February 2021 – full weekend closure between junctions 4b and 5

    The M4 will be closed in both directions over the weekend of 19 February – 22 February 2021 between Junctions 4b (M25 interchange) and 5 (Langley). The closure will start after 8pm Friday 19 February and the motorway will reopen by 6am on Monday 22 February.

     

    26 February to 1 March 2021 – full weekend closure between junctions 3 and 4b westbound and 4 and 4b eastbound

    The M4 will be closed over the weekend of 26 February – 1 March 2021 between Junctions 3 (Hayes) and 4b (M25 interchange) on the Westbound carriageway only and Junctions 4 (West Drayton) and 4b (M25 interchange) on the Eastbound carriageway only. The closures will start after 8pm Friday 26 February and the motorway will reopen by 6am on Monday 1 March.

     

    5 March to 8 March 2021 – full weekend closure between junctions 5 and 6

    The M4 will be closed in both directions over the weekend of 5 March – 8 March 2021 between Junctions 5 (Langley) and 6 (Slough). The closure will start after 8pm Friday 5 March and the motorway will reopen by 6am on Monday 8 March.

     

    12 March to 15 March 2021 – full weekend closure between junctions 6 and 7

    The M4 will be closed in both directions over the weekend of 12 March – 15 March 2021 between Junctions 6 (Slough) and 7 (Cippenham). The closure will start after 8pm Friday 12 March and the motorway will reopen by 6am on Monday 15 March.

     

    19 March to 22 March 2021 – full weekend closure between junctions 6 and 7

    The M4 will be closed in both directions over the weekend of 19 March – 22 March 2021 between Junctions 6 (Slough) and 7 (Cippenham). The closure will start after 8pm Friday 19 March and the motorway will reopen by 6am on Monday 22 March.

     

    26 March to 29 March 2021 – full weekend closure between junctions 5 and 6

    The M4 will be closed in both directions over the weekend of 26 March – 29 March 2021 between Junctions 5 (Langley) and 6 (Slough). The closure will start after 8pm Friday 26 March and the motorway will reopen by 6am on Monday 29 March.

    Please check before you travel.

    Our January 2021 scheme newsletter gives more information about full weekend closures of the M4 planned for 2021. There will be further updates on this page.

  • 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

Overview

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 x bridges which are being replaced as part of the project. The barrier in the central reservation will be replaced by a new concrete barrier. 

Through-junction running will be in place at There are several junctions on this stretch of the M4 which we will be changing so there’s a consistent number of lanes to pass through the junction This reduces the need to change lane for vehicles staying on the motorway. 

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.

Documents

Newsletters

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

Traffic information

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

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