Councillors have backed initial plans to connect some of Shetland's islands with undersea tunnels, which could be in place within eight years. A feasibility study proposed replacing ageing ferries with tunnels from Shetland's mainland to Yell and from Yell to Unst, describing them as "economically transformative". Two more tunnels, to the islands of Whalsay and Bressay, could follow under the plans - which it is estimated could cost £1.5bn. Council leaders say the tunnels would be cheaper than building new ferries and replacing harbours. At a meeting in Lerwick on Tuesday, councillors approved exploring funding options. Council chief executive Maggie Sandison said the project was not going to be easy, but she thought pursuing a funding solution was the "right thing to do". This could come from a mixture of private investment, public subsidy and borrowing, alongside tolls to cover maintenance costs. The council's transport chairperson, Moraig Lyall, said the report showed there were no technical barriers to building tunnels, which would be "cheaper in the long run" than ferries. Costs have risen sharply in the past decade, with some routes struggling to meet demand for vehicle places. Lyall said: "The system we have that has served us well for decades is now no longer able to do that. It doesn't have the capacity and we're struggling with other things, like the ability to crew the system adequately. These barriers to giving the islands a really good service are not going to be easily overcome by replacing ferries with other ferries. The tunnel is the answer that we believe will help us solve these problems."