Public transport advocacy group Future Transport Tasmania said it was working on a detailed plan to lobby the state government but a lot of information already pointed to the value of a high-speed train line.

Spokesman Toby Rowallan said the Liberal plan for a Launceston to Hobart four-lane highway would cost at least $3.6 billion, compared with $1.8 billion for the train.

Mr Rowallan said the service could consist of one train departing Hobart and another departing Launceston at the same time. 

The trains would cross (and stop) in the middle and result in a journey time of one hour, 15 minutes.

The $1.8 billion project cost would consist of: 

 --45 kilometres of new rail alignment or deviations costing $30 million a kilometre ($1.2 billion).

 --165 kilometres of upgraded existing rail costing $2 million a kilometre ($330 million).

 --New stations at Hobart, Launceston and the central crossing point ($50 million).

 --Two train sets (four power cars and four coaches, total $200 million) and miscellaneous costs,  $20 million.

A state government spokesman said Tasmania's population was too small to support a fast train, so instead the government was investing to make industry more efficient and to grow the economy, including seeking funding for 22 infrastructure projects.

TasRail chief executive Damien White said the railway was focused on restoring freight traffic and did not run passenger services.

Mr White said there were many difficulties and costs facing a fast rail service, including the need for new track, crossing loops, passenger platforms, amenities and ticketing, new train control methods, boom gates or a higher level of protection in urban areas.

Opposition infrastructure spokesman Rene Hidding said Tasmania needed an integrated system of road and rail transport, and it was not a case of one or the other.