AN undersea tunnel between mainland Shetland and the island of Yell would cost £402 million and take eight years to complete, it has been estimated.
Engineering consultancy firm COWI, who has been working alongside Shetland Islands Council (SIC) and consultants from Stantec, have published the estimations in a fresh report.
The group have been collaborating on a study weighing up the merits of improved ferry links and fixed link options such as bridges or subsea tunnels.
Councillors previously agreed to fund a study to establish the commercial and financial viability of tunnels and the future steps required to move the project forward.
It came after a report on Shetland’s future inter-island transport recommended enhanced ferry services for Fetlar, Foula, Papa Stour and Skerries, together with the case for tunnels to Bressay, Unst, Whalsay and Yell.
Yell was selected as the test subject, and the estimate is based on a potential 4.2 mile tunnel at a depth of 50m (165ft) connecting the island to the mainland of Shetland.
The tunnel would include tolls to cover maintenance costs.
Executive vice president of COWI Andy Sloan has said the £402m estimate is based on discussions with three international contractors.
Sloan said: "The capital cost investment is about £327m.
"On top of that we need to add risk and contingency money of £50m and upfront costs of £25m."
"While it seems like a big number, in a Scotland or UK-wide context it's entirely reasonable", said Sloan.
Tunnelling is estimated to take three years for preliminary work and five years for construction, according to the timeline published.
Director with SIC Neil Grant said both the UK and Scottish governments had shown interest, and added: "The Scottish government, in particular, has been supportive of the work to date."
The report will go before councillors on June 30.
Separate pre-seismic studies were carried out by Norconsult, the engineering consultancy firm behind the Faroe Islands’ subsea tunnels, in 2025 and followed on from reviews of earlier investigations into the feasibility of subsea rock tunnels across Bluemull Sound and Yell Sound.
