Lower Thames Crossing TBM tender: design, cost and schedule notes for engineers
Reviewed by Tom Sullivan
First reported on The Construction Index
30 Second Briefing
Bouygues Travaux Publics Murphy Joint Venture has started tendering for a 16.4 m diameter tunnel boring machine to drive the 4 km twin-bore road tunnel at the centre of the Lower Thames Crossing, set to carry three lanes of traffic in each direction and become the UK’s longest road tunnel. The move comes as project costs have risen from £9bn to £11bn, with £3bn expected from the public purse and the remainder likely under a regulated asset base model still subject to market engagement. TBM procurement is targeted for 2025, with tunnelling to start in 2028 from the northern portal and opening aimed for the early 2030s.
Technical Brief
- TBM specification is set at 16.4 m diameter, targeting one of the world’s widest road bores.
- Bouygues Travaux Publics Murphy JV has formally invited TBM tenders ahead of financial close.
- Government has allocated an additional £891m in the autumn budget for publicly funded enabling works.
- Current cost estimate has risen to £11bn, with about £3bn expected directly from public funds.
- Regulated asset base (RAB) model is the preferred financing option “at this stage”, subject to market feedback.
- Construction and subsequent operation beyond the publicly funded phase are intended to be privately financed and delivered.
- Northern portal construction, including TBM launch infrastructure, is scheduled to commence next summer despite funding uncertainty.
Our Take
With the Lower Thames Crossing cost range moving from £9bn to £11bn while only about £3bn is expected from direct public funding, the scheme is likely to sit at the upper end of UK road-project cost intensity in our Infrastructure database, putting pressure on toll and traffic assumptions to close the gap.
A 16.4 m TBM for a more-than-4 km twin-bore road tunnel places the Bouygues Travaux Publics Murphy JV among the few UK-based contractors preparing to handle mega-diameter soft-ground machines; this tends to narrow the pool of viable TBM suppliers and can lengthen procurement lead times into the ‘next year’ window mentioned.
Among recent UK Infrastructure pieces in our coverage, very few involve single assets with over £10bn capex and early TBM procurement, which suggests National Highways is trying to de-risk schedule on the Lower Thames Crossing ahead of the 2028–early 2030s delivery horizon rather than wait for full cost certainty.
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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