A new train line, which would be a multi-billion pound project, could finally give a major airport a station.

The Bristol Airport Rail Link has been proposed since 2006, hoping to connect the city to the airport in a line of just over nine miles.

The Mayor of Bristol Marvin Rees then put plans for the transport system forward in his State of the City Address in 2017 after it was an election campaign pledge.

Last summer, the West of England metro mayor and West of England Combined Authority (WECA) lead Dan Norris authorised a £15m study into the costs and feasibility of such a project.

Previous estimates of the Bristol Airport Rail Link have placed the cost of full construction between £4bn and £18bn, according to the New Civil Engineer.

Mr Norris has said that the authority believes the project would be the “right thing to do” even though the costs to build four new lines in Bristol make it nearly impossible.

Speaking on BBC Radio, he said: “We've got enough money to carry on the study for now. I think the project is so unlikely as to be not possible but we still continue to look at all the different options that are being considered, because that's the sensible and right thing to do.”

Currently, proposals put forward would see the construction of four rail lines from Bristol to Bath, Bristol Airport, Emersons Green and Cribbs Causeway.

A tunnelling expert told the New Civil Engineer that any subsurface work needed to construct the proposed Bristol underground would be “relatively easy”.

Mr Norris said: “At the moment we have to do a cost-benefit analysis of all the different options that are currently being considered, one of which is the underground system that Marvin's keen on. Underground rail is hugely expensive and the whole economic situation has changed.

But Bristol Airport told the Express that it would support such a project by the local authority as it could potentially “transform Bristol”.

A spokesperson said: “A mass transit system would transform Bristol and the surrounding region. It would boost productivity and growth, improve air quality, cut emissions, and allow people to travel predictably and with confidence to destinations across our city region.

“Bristol Airport is a key origin and destination for people moving around our region – travelling to and from our international gateway. We stand ready to work with bold and unified local leadership to design and deliver a mass transit system.”

Express.co.uk contacted West of England Combined Authority but at the time of publication, a comment had not been received.