The NCRA or NWP have done a few studies and forecasts over the years to help predict the volume of freight traffic. The accuracy is subject to conjecture; nobody will know for sure until it is running. Apparently it was enough for the state legislature to set up the NCRA and for many NCRA board members to serve many years as part of a challenging effort.
One aspect that is rarely mentioned is how a railroad brings transportation capability that is not possible on a highway. Some businesses cannot exist without a railroad; some products will not be transported into an area without it. Examples are aggregate for roadbuilding, lumber and grains. I'm sure there are others. Aggregate can run as low as $2.50 per ton at a gravel mine. Put 20 tons on a truck, and you have a meager $50 of product. The major expense at that point is the cost of the driver and the truck. A railroad will lower the cost of transporation by at least a factor of 4, probably much more.
Suppose you want an 80 ton object delivered across the country. A standard flatbed carries no more than 20 tons. You can probably put 80 tons on a heavy duty flatbed pulled by a tractor, but it requires special routes, special trailers and plenty of permits. I believe a single railroad flatcar is capable of carrying up to 100 tons. Someone please correct me if I'm wrong.
A railroad brings more transporation capability to an area; it may not be financially quantifiable or justifiable in a short term.