OK, trucks in most states can carry 80,000lbs-truck tare of 10,000 = 70,000 # of load. At 7 mpg, that is 245 ton-miles / gal.
So, rail is ~ 2x more fuel efficient than trucks.
More to follow.
I’m following your math.
70K lbs is 35 tons. So that is 35 gal of diesel for CSX to carry the same load as a truck 500 miles. 500 / 35 is 14mpg.
So that is 2x if the truck gets 7mpg fully loaded. But remember that for each load you need a truck driver but the monorail is automated with a few people monitoring thousands of loads. Hence my 2.5x factor for truck operating costs.
And according to this:
http://www.dieselserviceandsupply.com/Diesel_Fuel_Consumption.aspx
larger diesel generators are more efficient than the 50 cent/kwh figure. I think we can assume diesel electric trains are using the largest, most efficient diesel generators. The largest one on this list appears to produce electricity for 29 cents/kwh. So instead of a 5x factor for cheaper grid electricity, it looks like only a factor of 3x (29 cents vs 10 cents).
That would make the grid-electric powered monorail system only 7.5x as cost efficient as trucks. That is 13 pennies on the dollar rather than 8 pennies.