Just the salaries alone, for an eight-hour run, are staggering. Then there is the problem of maintaining 120 trucks, and all their tires and brakes. The railroad only has two locomotives to worry about. Truck tires might need to be replaced twice a year. A wheel on a locomotive might last at least five and probably ten years.
Trains are cheaper to run.
One train does what 120 to 180 trucks might do. Revenue cars are those which earn a railroad money. They include freight and passenger cars. By means of them, the railroad does the job for which it is paid. There are two ways this works.