Public transport advocacy group Future Transport Tasmania wants the state and federal governments to establish a fast rail link between Launceston and Hobart, using money the Liberal Party wants to find to upgrade the Midland Highway to four lanes between the two cities.

Future Transport Tasmania spokesman Toby Rowallan said the group was suggesting this because the Liberal plan would involve billions of dollars from the federal government to upgrade the road, which was new money.

Mr Rowallan said the group wanted the rail plan to replace the highway proposal.

He said the highway plan, based on Liberal Party figures and information on road building costs, would cost at least $3.6billion, but the budget could easily blow out, as other road projects had done.

Opposition Leader Tony Abbott has only committed to providing $400 million over a decade for the highway upgrade.

Mr Abbott said that, if elected next year, funding would start in 2014-15 and the project would be fully costed.

Mr Rowallan estimated the fast rail project would cost $1.8 billion, and even with a 20 per cent blowout would still only cost $2.2billion, much less than the highway cost.

He said the group envisaged a service using two trains, one departing from Hobart and the other Launceston, both leaving at the same time at each end.

The trains would cross, and stop, in the middle. This would remove any North-South rivalry.

With a journey time of 75 minutes (including a five-minute stop in the centre), travellers could relax in their chair or go to the buffet car.

With such a turn-around time, several trips could be managed each day.

Government business could be mandated to use it, thus saving on expensive vehicle fleet costs, and commercial activity could be encouraged by the construction of a conference centre at the station in the Midlands where the trains cross.

Buses could connect to the train in the Midlands, Hobart and Launceston.

The train would reduce highway traffic and crashes and reduce the state's carbon emissions.

The rail project would consist of:

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

•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 ($200million).

•Miscellaneous costs ($20million).

Mr Rowallan said the rail service could use trains like the Tilt Train, used by Queensland Rail. These trains can run at more than 200km/h, but are run at slower speeds.