National Highways is set to replace two key bridge expansion joints at the M25 and M4 interchange near Heathrow. These joints, carrying traffic on around 200,000 vehicles daily, have been in service for approximately 40 years.
Bridge joints allow vital movement
Expansion joints enable controlled movement within bridge structures, accommodating temperature changes and traffic loads while maintaining smooth carriageway surfaces. Over time, these joints wear and need replacing to maintain safety and reliability.
At M25 junction 15, the two major joints require full replacement rather than routine maintenance, reflecting their age and critical role within the network.
Traffic managed with targeted closures
Work preparation begins with two extended overnight closures. The M25 anticlockwise carriageway between the M4 slip roads will close from 8pm to 10am on Saturday 17 and 24 October 2026. During these periods, the clockwise carriageway and all M25-M4 links stay open.
Traffic diverted from the closed anticlockwise carriageway will leave at junction 15, follow the M4 westbound to junction 5, reverse direction at Langley Interchange, then return eastbound on the M4 before rejoining the M25 at junction 4b.
Weekday night closures will follow, operating between 10pm and 6am with diversions via M4 junction 4 and back, allowing preparatory work to proceed.
Joint replacement staged through 2027
The first main joint replacement will start in January 2027 on the M25 anticlockwise carriageway, continuing through to spring. The clockwise joint replacement will occur later in 2027, with exact dates pending.
Longest closures on both carriageways will be limited to 14 hours, minimising disruption and concentrating work overnight from Saturday into Sunday mornings.
Temporary ramps keep traffic flowing
National Highways has designed bespoke temporary ramps to place directly over the exposed expansion joints. These ramps enable the M25 to reopen each day at the national speed limit while work continues overnight.
This approach allows continuous motorway operation, reducing the impact of the structural work on one of the UK's busiest motorway sections.
Lessons in maintaining critical infrastructure
The M25 and M4 interchange shows how maintenance must be carefully coordinated with traffic management. Complete closures would simplify engineering but risk wider network delays affecting drivers beyond the immediate site.
Similar network effects have appeared on other major routes, including the M60, where extended closures led to significant delays outside the works zone.
Minimal disruption the objective
Drivers face diversion routes and some residual delays, especially between 8am and midday on Sundays following closures. National Highways expects these measures to maintain safety and journey reliability while carrying out essential infrastructure renewal.
Replacing ageing bridge components while keeping traffic moving reflects the practical challenges of maintaining the strategic road network. The best repair is often one that goes unnoticed by the majority of users because it is planned around traffic flow.
