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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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
We need to keep the elevated section of the M4 safe and useable for the 100,000 people who use it each day. This survey work will ensure we continue to do so. We have chosen overnight work to try to minimise disruption as much as possible.
Benefits
Our survey work will ensure we keep the elevated section of the M4 safe and useable for the 100,000 people who use it each day.
Documents
Traffic information
Information about scheduled roadworks and events on our motorways and major roads.Sign up for updates!
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