The US state of Minnesota's proposed rail project Northern Lights Express (NLX) has been estimated to cost nearly $1bn by the transport department.
The project was recently estimated at $615m by its proponents, which is nearly double the 2008 estimate of $360m.
The project involves building a 155-mile rail line between Minneapolis and Duluth to provide a two-hour service via Cambridge, Hinckley, Sandstone and Superior.
The new estimation is the worst-case scenario for the project and the plan will stick with $990m as the high range of the cost, according to the state's Department of Transportation (DoT).
Consultants from the DoT and NLX now need to reach an agreement on the cost of the rail line in the next few weeks to allow the state to submit an application for federal funding.
The federal funds, for which 40 other US states are competing, are expected to fund 80% of the project.