An underground rail network costing at least $105 million a kilometre to build is one of eight options being proposed by the Wellington regional council to improve the city's public transport.
Options include a revamped bus system, electric light rail and heavy rail above or below the ground to run between the train station and the hospital.
Regional councillor in charge of transport Peter Glensor says underground rail is very expensive and that could stop it from going any further.
The council will narrow the eight options down to four by June, and those will go out for public consultation early next year.
Mr Glensor says construction could be several years away and negotiations with the Government are underway on who would pay for the new system.