One of the justifications for the High Speed Rail project was an anticipated increase in freight traffic — a 50% increase by the year 2040, as I recall (I cannot locate the source on the dc2rvarail web site – maybe someone could help me). This increase would require that a third track be installed.
But projections of a large increase in freight traffic may turn out to be inaccurate. One of the more important cargoes is coal yet, as the chart below shows, coal traffic by rail in the United States decreased by 15% during 2015; from January 2015 to January 2016 it is down 31%. It is questionable if coal traffic will return to its earlier levels given environmental pressures and the economics of natural gas.
If the price of fuel goes up then there may be a gradual shift from eighteen wheelers to the trains. Still, I wonder if we will see the increases that are projected.