Despite that the costs to construct the Silvertown Tunnel in east London have risen by £2M and the project’s opening date has been postponed, Transport for London (TfL) remains confident that it can recoup the funds.
While the determined final costs on the agenda for the meeting of TfL’s Program and Investments committee on 5 October for the project is £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 and effort of TfL was to reduce this by £9M in the middle of the year through reduction in risk exposure.
According to TfL: "The latest £2M cost spike is due to a reassessment of some of the key risks, which are being managed and mitigations developed."
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."
Located under the Thames River, the new 1.4km twin bore road tunnel has faced much advance in the last six months.
In order to completing its second drive beneath the river some 62 days ahead of schedule, the project’s enormous tunnel boring machine (TBM) arrived in Newham in July.
Following broke through into the Greenwich rotation chamber, where it was rotated using an innovative nitrogen skate method in a UK first, the TBM completed its first excavation process in February 2023.
Additionally, June 2023 was the date of inaugurating the new accessible Boord Street foot and cycle bridge.
The responsibility of constructing this tunnel is up to Riverlinx CJV, a joint venture of Bam Nuttall, Ferrovial and SK Ecoplant, which is also going to 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.
While the expenses of this project were £117M until now, another £62M is forecast to be spent before completion.
Additionally, the target opening date for Silvertown Tunnel has slipped into Q2 of 2025/2026, meaning July to September 2025. Due to previous delays it had gradually slipped from April to June, remaining in Q1, but a recent 18-day delay has been enough to see it pushed into July, which is the next quarter.
"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," added TfL.
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 analyzing the roughly 750 responses before deciding on the next steps.