There has been much progress on the new 1.4km twin-bore road tunnel beneath the Thames River in the last six months. This has included the successful rotation of the tunnel boring machine (TBM) using an innovative nitrogen skate method (the first of its kind in the UK) and the completion of the second bore some 62 days ahead of schedule. The new accessible Boord Street foot and cycle bridge opened in June.

As revealed in the agenda for the meeting of TfL’s Programmes and Investments committee on 5 October, the EFC of the tunnel now sits at £179M. This is £6M over the approved authority of £173M and a £2M increase on the previous quarterly forecast of £177M.

However, this is down from the peak cost forecast from early this year which saw the EFC hit £186M. TfL managed to bring this down by £9M in the middle of the year through reduction in risk exposure.

The latest £2M cost spike is due to “a reassessment of some of the key risks, which are being managed and mitigations developed” according to TfL.

It adds: “We continue to seek opportunities to reduce cost and risk exposure, which should be achievable to bring us back in line with the authority.”

The tunnel is being constructed by Riverlinx CJV, a joint venture of Bam Nuttall, Ferrovial and SK Ecoplant, which will also maintain the tunnel for 25 years after opening. It is privately financing the majority of the costs, which TfL will repay over the 25 years in “availability payments” subject to Riverlinx’s performance in maintaining it.

To date, £117M has been spent on the project and another £62M is forecast to be spent before completion.

How Silvertown Tunnel’s EFC and opening date have changed over time

Additionally, the target opening date for Silvertown Tunnel has slipped into Q2 of 2025/2026 (i.e. July to September 2025). Due to previous delays it had gradually slipped from April to June, remaining in Q1, but the latest 18-day delay has been enough to see it pushed into July, which is the next quarter.

The slippage has been caused by “a change in programme sequencing to allow for equipment installation to take place after the removal of the [TBM]”.

It adds: “Both TfL and Riverlinx are working hard to bring the permit to use back into Quarter 1 25/26 […] Mitigations are underway to allow for some parts of the TBM to be removed back through Greenwich rather than Silvertown. These have already reduced the potential impact of the equipment installation from 49 to 18 days.”

Separately, TfL is also seeking approval for an additional unbudgeted £2.7M from the Financial Authority and Programme and Project Authority for associated bus infrastructure improvements around the Silvertown Tunnel.

Contracts for the bus services through Silvertown Tunnel – including routes 129 and Superloop 4 – were awarded to Go-Ahead London this year. It includes a commitment that all the buses on these routes will be zero emissions from the start of operation and that appropriate driver and customer facilities will be provided along the route.

The expanded scope for the buses and the facilities will require an estimated further £2.7M, but this won’t be added to Riverlinx’s costs – it will be funded through TfL’s budget and business plan if approved.

TfL recently carried out a public consultation into its proposal to set up a shuttlebus service for cyclists through both the Silvertown and Blackwall tunnels. This closed on 10 September and TfL is now analysing the 750-or-so responses before deciding on the next steps.

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