A Ford Excursion, getting 10 mpg, when loaded to its capacity of eight passengers, gets 80 passenger miles per gallon. Ton/miles per gallon is not a measure of consumption, but of efficiency.
I need to move 400 tons of (800,000 lbs) of stuff 423 miles. A a truck hauling 80,000 lbs gets about 4 miles to the gallon, IIRC last time I was looking at peterbilts. So to move that 400 tons, I need 10 trucks. So I am going to move these items .4 miles for every gallon consumed, so to travel the distance of 423 miles, I need to us 1057 gallons of diesel fuel. Alternatively, I can tack it onto the back of a freight train (CSX isn't all that much more efficient than its competitors, btw), and it will take 400 gallons. So this 18-wheeler moves one ton of freight 162 miles.
It ain't a ridiculous increase in efficiency, you understand. About 2.5 times. But its a big solid demonstration of the advantage of moving things in bulk.
To further the comparison, let us move these 400 tons of stuff via a Ford F350 with single rear wheels, which can carry 4000 lbs, or 2 tons worth of stuff. It gets around 10mpg fully loaded. To carry 400 tons, you need 200 F350s. It will take 42.3 gallons of fuel per truck to do the move, or a total of 8460 gallons of fuel. This F350 moves 1 ton of frieght 20 miles per gallon of fuel.
Its the best way to measure haulage efficiency of bulk freight. And in this regard, the railroad is clearly superior.