Costain’s £100M M5 Somerset junction: design and risk notes for civils teams
Reviewed by Joe Ashwell
First reported on New Civil Engineer
30 Second Briefing
Costain has secured a £100M, five-year design-and-build contract for a new junction on the M5 near Bridgwater, Somerset, to provide direct access to a planned gigafactory site. The scheme will require complex tie-ins to live motorway carriageways and associated slip roads, with staging and traffic management critical on this heavily trafficked strategic corridor. For geotechnical and civils teams, early ground investigation, settlement control around existing pavements, and drainage upgrades to motorway standards will be key risk drivers.
Technical Brief
- Contract value of about £100M indicates major civils and geotechnical work scope over the programme.
- Five-year duration suggests extended design development, statutory process, and staged construction under traffic.
- Junction is being delivered specifically to serve a planned gigafactory, so heavy goods access geometry will dominate.
- Long contract period allows early contractor involvement-style optimisation of earthworks balance and materials sourcing.
- Similar motorway access schemes for large industrial hubs (e.g. logistics parks) show growing co-dependency between highways and private-sector mega-projects.
Our Take
Costain’s presence across multiple major UK schemes in our database – from HS2’s Skanska Costain Strabag JV tunnels to leadership changes linked with Sizewell C – suggests this Somerset road contract reinforces its positioning as a go‑to Tier 1 for nationally significant infrastructure.
A five‑year programme for the new M5 junction aligns with the longer delivery horizons seen on other Costain‑involved corridors in our coverage, which typically allows integration of traffic management, digital monitoring and staged handover to minimise disruption on strategic routes.
Among the 547 Infrastructure stories in our database, relatively few regional highway upgrades are directly tied to gigafactory access, so this Somerset scheme is likely to become a reference case for how UK roads agencies and OEM‑linked investors structure enabling works for battery manufacturing clusters.
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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