AN INDEPENDENT report suggests the Melbourne- Brisbane Inland Rail route could be cheaper and faster via Karara, rather than Millmerran.

The report tabled by Member for Southern Downs Lawrence Springborg this week was published in 2015 but was never made public, according to the MP.

Now, Mr Springborg is asking why the report had not been brought to light earlier.

"All I want is a proper, transparent process, and this report sheds some light (on deciding a route)," Mr Springborg said.

"The process that has been secretive, it's been questionable and all the (Australian Rail Track Corporation) does is talk in riddles."

Snowy Mountains Engineering Corporation's (SMRC) report revealed a route passing through Leyburn and Karara would cost $100 million less than the proposed corridor via Millmerran.

The 90-page report also said the Karara route did not encounter as many floodplain problems and was quicker than the proposed corridor through Millmerran.

As an MP for the impacted areas, Mr Springborg stressed he did not have a preferred route, but wanted the process of deciding one "done right".

"All options should be on the table and clearly to date that has not been the case," Mr Springborg said.

The assessment report was finalised in July 2015 and comes five years after the 2010 report relied upon by the ARTC and others to push for the current preferred corridor.

When asked why the route was not the preferred corridor, an ARTC spokesman said it was briefly considered.

"ARTC engaged consultants to undertake a further analysis of the route identified in the SMEC report, and the outcome of that analysis was that there wasn't a compelling case for the alternative route," he said.

"There will be an extensive and ongoing consultation process before a final decision on the inland rail corridor is made as part of the environmental and planning process."

The report said, "(the Karara route) has greater potential to attract freight from this regional centre (Warwick), with potentially a freight terminal in Karara".

"(It) also passes closer to the Felton group of coal deposits."

However, the ARTC spokesman disagreed.

"The preferred alignment (Inglewood to Gowrie) in the 2010 Alignment Study was identified because it allows for shorter journey time, reduced costs and enables greater freight volumes," he said.

"It's imperative that inland rail meets the freight industry's service level requirements as well as balancing construction costs, environmental and social considerations."

However, the SMEC report revealed the Millmerran route was the third most expensive of the four outlined in the study.

Warwick man Don McKechnie said it was concerning how firm the ARTC was already on the Millmerran corridor, despite still being in a "consultation process".

"It's been put forward as more than just a 'likely route', but I don't believe the engineers and the planners have taken in to account the physical problems the train could face the way and the very high costs," he said.

He said heavy black soil and the flood plain would prove particularly problematic and be "horribly costly" from an engineering perspective.

Mr Springborg said the report needed to be treated seriously in locking in a corridor. "This is a very extensive report, prepared with the full knowledge of the Queensland Government and ARTC and there is a very serious question as to why it has not been been previously released to the public, particularly given the issues it has raised about the various corridor options."

Strategic cost estimates

Via Millmerran$3.07b

Via Pittsworth and Southbrook$2.97b

Via Karara and Umbiram$2.97b

Via west Warwick and Wyreema$5.73b