M25 Junction 10 £317M upgrade: design, capacity and closure lessons for engineers
Reviewed by Tom Sullivan
First reported on New Civil Engineer
30 Second Briefing
£317M upgrade works on the M25’s Junction 10 in Surrey are now complete, with engineers widening the junction roundabout and adding a fourth lane on a key section of the A3 to increase capacity through one of the network’s busiest interchanges. The scheme, delivered for National Highways, also includes a new green bridge across the A3 to maintain ecological connectivity and non-motorised user routes over the widened carriageway. Construction required the first ever full weekend closures of the M25, signalling a precedent for future major interventions on the orbital.
Technical Brief
- Widened roundabout geometry required reconfiguration of approach alignments, drainage and verge/central reserve earthworks.
- Fourth A3 lane integration demanded pavement strengthening, revised lane markings and updated safety barrier layouts.
- Green bridge construction implies substantial retained approaches, habitat soil profiles and long-span deck detailing over live traffic.
- Delivery sequence will inform risk planning for other high‑volume corridors where full closures were previously considered untenable.
Our Take
National Highways features heavily in our infrastructure coverage, with the M25 Junction 10 works sitting alongside major schemes like the M3 Junction 9 upgrade and the Lower Thames Crossing TBM procurement, signalling a sustained push on strategic corridor capacity and resilience in the south of England.
The use of full weekend closures on the M25 contrasts with the more traditional phasing seen on schemes such as the M3 Junction 9 works, suggesting National Highways is increasingly willing to trade short, intense disruption for programme certainty on high‑value junction upgrades.
With Jacobs recently winning multiple National Highways design and asset renewal commissions on the M32 and M5, the completed M25/A3 package at Junction 10 is likely to serve as a reference point for how complex motorway junction upgrades are scoped and procured in the next wave of the UK’s strategic road network projects.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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