M25 junction 15 (M4 junction 4b) bridge repairs near Heathrow Airport

We're replacing two major bridge expansion joints.

Start date Autumn 2026

End date Winter 2027

Cost TBC

Latest updates

30 September 2026
Extended overnight closures, M25 junction 15 (anticlockwise) – October 2026

We’re doing preparatory work at M25 junction 15 ahead of the replacement of two major bridge expansion joints starting next year.

To complete this essential work safely we will require two extended overnight closures in October 2026.

The M25 junction 15 anticlockwise carriageway will be closed between the M4 slip roads from:
- 8pm Saturday 17 to 10am Sunday 18 October 2026
- 8pm Saturday 24 to 10am Sunday 25 October 2026
The M25 junction 15 clockwise carriageway and all links between the M25 and M4 will remain open throughout the works.

Diversion route

During both closures, M25 anticlockwise traffic will need to exit at junction 15.

There will be a fully signed diversion route in place to rejoin the M25 anticlockwise carriageway after the closure:
- follow the M4 westbound to junction 5
- turn around at M4 junction 5 (the Langley Interchange)
- return on the M4 eastbound to rejoin the M25 anticlockwise via M4 junction 4b
M25 junction 15 anticlockwise weekend closures diversion route map

The route will be busier than usual with residual delays expected on the M25 on Sunday after the closures have been removed.

If you must travel between these times

Please plan ahead and allow extra time for your journey

Travel earlier or later in the day - we’re expecting the busiest time around the M25/M4 interchange on Sunday mornings between 8am and midday

Where possible

Consider alternatives to avoid severe delays, including alternative routes or public transport (i,e, for Heathrow Airport, Heathrow Express, Elizabeth Line)

We'll complete some further works on weekday nights. These closures will take place between 10pm and 6am.

During weekday nights, a diversion will be in place to M4 junction 4 and return.

M25 junction 15 anticlockwise weeknight closures diversion route map

Construction – 2027

Following our preparation works in October 2026, a series of extended overnight closures will be required to replace the bridge expansion joints in 2027.

M25 anticlockwise

We will replace the bridge expansion joint on the M25 junction 15 anticlockwise carriageway first. Work here is expected to begin in January 2027 and be completed by Spring 2027.

M25 clockwise

The replacement of the M25 junction 15 clockwise expansion bridge joint is expected to happen later in 2027; dates are to be confirmed.

Our longest closures will be limited to 14 hours. To minimise disruption and complete work safely, these will be installed overnight on weekends, between 8pm on Saturdays and 10am on Sundays.

All other work will be completed during the week between 10pm and 6am.

For more information and to be kept up to date with these works please check this webpage for regular updates.

Please remember that closures can change at short notice. You can check the latest information on our daily closures page. Our travel alerts give details of live incidents on our network.

See more updates

Project information

To reduce disruption on one of the busiest motorway sections in the UK, bespoke temporary network ramps have been designed to fit over the joints whilst the work is taking place.

This means the M25 can be reopened to road users each day (at the National Speed Limit) and uncovered overnight to progress works.

This option avoids the need for more disruptive full weekend closures and means the work can take place when there is less traffic using the road.

The bridge expansion joints we are replacing have been in service for around 40 years.

This work is essential to help maintain safe and reliable journeys for the 200,000 vehicles that use this section of the M25 each day for decades to come.