A4 Great West Road, under the M4 in Brentford, West London
The elevated section of the M4 spans the A4 Great West Road in Brentford. It carries tens-of-thousands of journeys in and out of west London every day and helps keep motorway traffic separate from local roads. As part of our commitment to making sure this important viaduct remains safe and maintained, we’re repairing some of the reinforced concrete pillars which support the structure from the A4 Great West Road’s central reservation. We’ll need to continue this work periodically over the coming years.
Latest updates
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02 March 2026
Our next phase of work starts soon – March to November 2026
The next phase of our ongoing refurbishment programme to the concrete pillars beneath the M4 elevated section will begin shortly.
We'll focus on the eastern end of the M4 elevated section, between Chiswick Roundabout and Lionel Road.
We'll begin works on Monday 9 March and will continue for up to 35 weeks, with an anticipated completion date of Saturday 7 November 2026.
As with previous phases of this scheme, scaffolding will need to be erected around the pillars and traffic management installed within the A4 Great West Road central reservation to allow our teams to carry out the work safely.
Traffic management
To enable safe set-up of the works, the A4 Great West Road will be subject to overnight full closures on the following dates:
- Monday 9 and Tuesday 10 March (10pm-5am) - Chiswick Roundabout to Ealing Road (westbound)
- Wednesday 11 and Thursday 12 March (10pm-5am) - Ealing Road to Chiswick Roundabout (eastbound)
During both closures:
- the H91 bus service will be escorted through the closure
Access to affected properties and businesses will be maintained throughout - a signed diversion will be in place for all other traffic
The westbound diversion will be signed by:
- the A205 Chiswick High Road
- A315 High Street westbound
- and B455 Ealing Road northbound
The eastbound diversion will be signed by:
- the B455 Ealing Road southbound
- A315 High Street
- and A205 Chiswick High Road eastbound
On-going lane restrictions
Between March and November, a lane three closure on the A4 westbound carriageway will remain in place near the junction with Capital Interchange Way.
The two lanes designated for the M4 from the Chiswick Roundabout will remain open, with the third lane designated for the A4 available beyond the work area.
No lane closures will be required on the A4 eastbound carriageway. Pedestrian crossings and vehicle crossings over the A4 will not be affected by this phase of works.
About the scheme
This work is essential to maintaining the M4 elevated section in a safe and reliable condition. Due to the age of the structure, refurbishment works are ongoing and we'll expect this programme to continue over the coming years.
We'll plan to refurbish up to twelve pillars, in addition to the thirteen pillars already completed since 2023.
We apologise in advance for any inconvenience caused and thank you for your patience while we carry out this essential maintenance.
Please check back regularly for the latest updates on this scheme.
Please remember that closures can change at short notice. You can check the latest information on our daily closures page or find live travel information on our Traffic England site. Our travel alerts give details of live incidents on our network.
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13 February 2026
Night closures this weekend
Inspection work on the M4 elevated section continues this weekend.
We will be using mobile elevated working platforms under the viaduct to get up to date information on the condition of the structure.
To provide safe access, we will need to implement some overnight closures on the A4 Great West Road and the M4 between 8pm and 5am.
Friday 13 February (8pm to 5am)
The A4 will be closed eastbound between Boston Park Road and Ealing Road.
Buses will be escorted through the closure.
Diversions
A4 Eastbound traffic will be diverted via the:
- A3002 Boston Manor Road
- Half Acre southbound and the A315 High Street eastbound
- B455 Ealing Road northbound to rejoin the A4.
A diversion route for local traffic will be in place via:
- Windmill Road northbound
- Little Ealing Road eastbound and
- the B455 Ealing Road southbound to the A4
A4 eastbound diversion route map
Saturday 14 February (8pm to 5am)
The A4 will be closed westbound between the M4 junction 2 entry slip and Boston Manor Road.
The M4 will be closed westbound between junctions 1 and 2
Buses will be escorted through the closure.Diversions
A4 westbound traffic will be diverted via the:
- Chiswick Roundabout and the Chiswick High Road
- A315 High Street westbound and
- the A3002 Half Acre
- Boston Manor Road northbound to the A4
A4 eastbound traffic looking to cross over the A4 to head south will be diverted to the Chiswick Roundabout and return.
Motorway traffic looking to join the M4 westbound at junction 1 will be diverted to join via the junction 2 slip road, which will remain accessible from the A4 westbound.
Local diversion routes will be in place for Ealing Road and Windmill Road south of the A4
A4 westbound diversion route map
Sunday 15 February (8pm to 5am)
The east and west quadrants of the Ealing Road roundabout will be closed.
A4 east and westbound traffic will be able to continue straight ahead across the roundabout.
Diversions
Traffic looking to head south across the A4 / Ealing Road junction will be diverted eastbound to Clayponds Avenue and return.
Traffic looking to head north across the A4 / Ealing Road junction will be diverted westbound to Riverbank Way and return.
A4 / Ealing Road junction diversion route map
We sincerely apologise for the short notice of these works and for any disruption caused.
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06 February 2026
Short notice closures
Saturday 7 February (8pm-5am)
- The A4 will be closed eastbound between Ealing Road and Chiswick Roundabout
- The H91 bus service will be escorted through the closure
Fully signed diversion routes will be in place for all other traffic.
A4 eastbound traffic will be diverted by:
- B455 Ealing Road southbound
- A315 High Street eastbound to Chiswick Roundabout
A local diversion route for Lionel Road North will be in place by:
- the B4491 Popes Lane
- and B455 Ealing Rd
A local diversion for Clayponds Avenue will be in place by:
- Chestnut Avenue
- and the B455 Ealing Road
Sunday 8 February (8pm to 5am)
- The A4 will be closed westbound between the Chiswick Roundabout and Ealing Road
- Buses will be escorted through the closure
Fully signed diversion routes will be in place
Diversion:
- A4/M4 you will be diverted to M4 junction 1
- the Chiswick Roundabout
- A315 High Street westbound
- B455 Ealing road northbound
Please remember that closures can change at short notice. You can check the latest information on our daily closures page or find live travel information on our Traffic England site. Our travel alerts give details of live incidents on our network.
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17 November 2025
Final phase of work for this year
Closures and Diversion
Monday 17 November to Friday 21 November (10pm to 5am)
- There will be night time temporary three-way traffic lights on Boston Manor Road between the A4 Great West Road and Manor Vale
Wednesday 19 and Thursday 20 November (10pm to 5am)
- The A4 will be closed at night on in both directions between Boston Manor Road and Ealing Road.
The H91 bus service will be escorted through the closure.
Fully signed diversion routes will be in place by
- the A315 High Street
- B455 Ealing Road
- and A3002 Boston Manor Road for all other traffic
The outside lane of the A4 between Boston Manor Road and Ealing Road and the vehicle and pedestrian crossings at Windmill Road, will be fully reopened by the morning of Friday 21 November.
Bus stops SZ and SY, and several nearby parking bays, will be suspended during working hours and temporary pedestrian crossings will be installed. Access to affected businesses will be maintained.
We’d sincerely like to thank residents, businesses, all road users and the local community for their patience while we continue the essential work this year.
We expect our next phase of work to happen in 2026, towards the eastern end of the M4 elevated section near junction 1.
Further details will be shared as plans are confirmed so please check back here for updates. Some other routine work, such as principal structure inspections, will continue as part of our ongoing monitoring and maintenance regime.
Please remember that closures can change at short notice. You can check the latest information on our daily closures page or find live travel information on our Traffic England site. Our travel alerts give details of live incidents on our network.
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15 September 2025
Progress update and closures
Our current phase of refurbishment work to the M4 elevated section is due to be completed by Saturday 29 November 2025.
Since July, we’ve been refurbishing three of the concrete pillars located east of Windmill Road. We’ve installed additional reinforcing steel and applied new concrete to improve their current condition and keep them safe for the future.
You will see us removing scaffolding from around these pillars over the next several days as we complete our final checks and prepare to begin work to the west of Windmill Road.
To move to this next stage, the A4 will be closed at night next week while we adjust the start and end point of the existing traffic management.
During this time, the A4 pedestrian crossing east of Windmill Road, which has been closed since July, will be re-opened, and the A4 pedestrian crossing west of Windmill Road will be closed.
Monday 15 to Friday 19 September 2025 (10pm to 5am)
- the A4 will be closed each night in both directions between Boston Manor Road and Ealing Road
- the H91 bus service will be escorted through the closure
Fully signed diversion routes will be in place by:
- the A315 High Street
- B455 Ealing Road and A3002 Boston Manor Road for all other traffic
Saturday 20 September to Saturday 29 November 2025 (24 hours a day)
- lane 3 will continue to be closed in both directions on the A4 between Boston Manor Road and Ealing Road
- the Windmill Road crossing over the A4 will continue to be closed to vehicles
- the A4 pedestrian crossing west of Windmill Road will be closed
- the A4 pedestrian crossing east of Windmill Road will be open
Public transport
Whilst we're working, local bus services may be delayed during busy periods.
The E2 service is following a short diversion along Windmill Road until 29 November.
- buses towards Brentford are missing stops at Orchard Road (SC) and Boston Manor Road (SD)
- buses towards Greenford are diverted by A4 but no stops are missed
You can find live status updates for the E2 service on the Transport for London website.
Pedestrians and cyclists
The A4 crossing east of Windmill Road will be re-opened next week before the crossing west of Windmill Road is closed, ensuring one crossing always remains available to pedestrians. Cycling routes remain unaffected.
Residents and businesses
We're working to keep disruption to a minimum, with specialist equipment on site to monitor noise levels throughout the project.
As our work continues, we recommend you:
- allow extra time for your journey
- use alternative routes where possible
- travel outside peak times if you can
- consider other transport options for local trips
Thank you for your continued patience and understanding while this essential work is underway.
Please check this page for updates.
Please remember that closures can change at short notice. You can check the latest information on our daily closures page or find live travel information on our Traffic England. Our travel alerts give details of live incidents on our network.
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07 August 2025
M4 viaduct refurbishment work - until 29 November 2025
Work
We're carrying out essential refurbishment work to keep the M4 viaduct safe and reliable. This elevated section carries the M4 over West London.
We've set up a safe working area in the A4 central reservation and started removing old concrete sections using high-pressure water jets.
Our work areas are enclosed to reduce noise and dust.
Work hours: 7am to 7pm daily
Project end date: Saturday 29 November 2025Closures
Road closures until 29 November 2025 (24 hours a day):
- Lane 3 closed in both directions on the A4 between Boston Manor Road and Ealing Road
- You cannot cross the A4 at Windmill Road junction (north to south or south to north)
- A4 pedestrian crossing east of Windmill Road is closed
- A4 pedestrian crossing west of Windmill Road remains open
Expect delays on the A4 through Brentford, especially during rush hours.
What you can do:
- Allow extra time for your journey
- Use alternative routes where possible
- Travel outside peak times if you can
- Consider other transport options for local trips
Public transport
Buses: Services may be delayed during busy periods. Affected routes include 65, 195, 235, 237, 267, E2, E8, H91, N9 and N65.
E2 bus service changes: The E2 is following a short diversion along Windmill Road until 29 November.
- Buses towards Brentford: missing stops at Orchard Road (SC) and Boston Manor Road (SD)
- Buses towards Greenford: diverted via A4 but no stops missed
A4 Great West Road bus route diversion
Pedestrians and cyclists
Pedestrians: The A4 crossing east of Windmill Road is closed, but the crossing west of Windmill Road is open.
We'll need to switch these closures around in October, but one crossing will always remain open.
Cyclists: All cycling routes remain unaffected.
For residents and businesses
We're working to keep disruption to a minimum. All businesses remain accessible and we're monitoring noise levels throughout the project.
Our work takes place between 7am and 7pm to avoid overnight noise.
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23 June 2025
Boston Manor Road to Ealing Road refurbishment work
We'll be working on the A4 Great West Road between Boston Manor Road and Ealing Road for 21 weeks, from Monday 7 July to Saturday 29 November 2025.
There will be overnight closures from Monday 7 July 2025 to safely install traffic management and scaffolding.
The A4 will be closed each night in both directions between Boston Manor Road and Ealing Road.
Fully signed diversion routes will be in place via the A315 High Street, B455 Ealing Road and A3002 Boston Manor Road
From Monday 14 July until Saturday 29 November 2025 (24 hours a day) the following arrangements will remain in place to ensure the safe delivery of the refurbishment works:
- Lane three of the A4 will be closed in both directions between Boston Manor Road and Ealing Road
- One of the two available A4 pedestrian crossings at Windmill Road will be closed
Due to the above lane closures, it won’t be possible to drive across the A4 north to south, or south to north, at the Windmill Road junction.
Driving
We’re expecting delays on the A4 through Brentford at peak times.
Please consider:
- allowing extra time for journeys
- using alternative routes or retiming your journey to off-peak times if possible
- alternative modes of transport for local journeys if possible
Buses
Services may be delayed through the area during busier times. The routes affected include 65, 195, 235, 237, 267, E2, E8, H91, N9 and N65.
The E2 service will follow a short diversion route at the A4 to continue its journey along Windmill Road.
Walking and cycling
Due to the close proximity to our construction work, we’ll need to close one of the two A4 pedestrian crossing points at Windmill Road for safety. We’ll need to switch these closures around at approximately the half-way point of our work.
There will always be one A4 pedestrian crossing point open at Windmill Road throughout the duration of our works.
Cycling routes will be unaffected.
Residents and businesses
We’ll make every effort to limit disruption to residents and businesses. Our work areas will be enclosed to reduce noise and access to businesses will be maintained.
Please check this page for updates.
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14 April 2025
Survey work starts soon
We need to survey the concrete pillars that are part of the elevated section of the M4 in Brentford, West London.
To safely access the pillars from ground level, we will close sections of the A4 Great West Road, which is under the M4, overnight.
We have chosen overnight closures to minimise disruption as much as possible.
The A4 will be closed between 10pm and 5am:
Eastbound, between Ealing Road and the Chiswick Roundabout, from Tuesday 27 May for seven nights
Westbound, between the Chiswick Roundabout and Ealing Road, from Tuesday 3 June for seven nights
East and westbound, between Boston Manor Road and Ealing Road, on Thursday 12 and Friday 13 June
East and westbound diversion map
There will be overnight lane closures on the A4 east and westbound, at Ealing Road, on Tuesday 10 and Wednesday 11 June.
Please allow extra travel time if driving overnight. The road will be reopened by 5am each morning and remain open throughout the day.
Access for drivers
Fully signposted diversion routes will be in place overnight via the:
- Chiswick Roundabout and the A315 High Street, using the B455 Ealing Road or A3002 Boston Manor Road, depending on which section is closed
- A4 westbound to the Waggoners Roundabout and the A312. The Parkway northbound for access to the M4 via junction 3
For residents and businesses
Access to the side roads directly off the A4 where it is closed will be maintained for residents and businesses. Please speak to a member of our team on site who will escort you through the closure to your property when it is safe to do so. Our work will consist of visual inspections and hammer tap inspections which shouldn’t cause any major noise disturbance.
Bus services
We’ve made special provisions to safely escort buses through our closures, where required. This also applies to emergency services responding to incidents.
We plan to carry out further works here to keep the elevated section of the M4 safe and useable for the 100,000 people who use it each day. Please check back for updates.
Project information
Overview
Built in the 1960s, the elevated section of the M4 is a large viaduct which runs directly above the A4 Great West Road in Brentford. Located between Heathrow Airport and central London, it plays an important role in connecting people and is essential to the movement of goods. It is used by around 100,000 vehicles each day.
Over time, damage from water runoff, and salt used in winter maintenance activities, can reduce the strength and condition of the concrete, which is to be expected of a structure of this age and construction.
Over the next five to ten years, one of our key focusses is to restore the condition of the viaduct’s supporting concrete pillars. This work is essential for the continued safety of all who use the viaduct and to protect journey times on both the M4 elevated section and the A4 Great West Road.
Benefits
As part of our commitment to ensuring this important viaduct remains safe and reliable, the repairs we’re carrying out to the viaduct’s supporting concrete pillars will improve their condition and keep them safe for the next 15+ years. The work will help ensure the viaduct can continue to facilitate larger vehicles without any restrictions and keep long-distance and local journeys separated.
Since 2010, we’ve carried out various other essential works to prolong the lifespan of the structure. This has included waterproofing work, replacing expansion joints, concrete repairs, and the externalisation of the structure’s drainage to prevent water ingress.
We’ll continue to carry out routine structural and maintenance work, and monitoring and inspections, to keep the viaduct safe for the future.
Documents
Traffic information
Information about scheduled roadworks and events on our motorways and major roads.Sign up for updates!
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