Single track vs. double has many variables:
Are we talking about two tracks, each for one direction with automatic block signals or two tracks each bidirectional, frequent high-speed crossovers (now imported, movable frogs, etc.) and CTC or equivalent?
Is the single track equipped with really long passing sidings enabling non-stop meets or are the sidings barely long enough to contain the typical or maximum train lengths operated? CTC or equivalent is assumed, of course. What about siding spacing?
Is the traffic “fleeted”, like 54 wesbonds 9AM - 9PM and then 54 eastbounds 9PM - 9AM, or is traffic in both directions spread pretty evenly throughout the day?
Is there a mixture of moderate speed coal and mineral trains and also high-speed intermodal, or do all trains run at about the same speed?
Is the double track going to be complete or will there be somethiing like the Aroya Canyon single-track bottleneck?