Since running prototype length trains on even a large layout consumes too much space, we have to compromise. My coal train lengths are generally around 24-25 cars, representing what I figure would be a typical 96-100 car train on the prototype. Most modern unit trains I see here in the eastern US (NS and CSX) are within that length.
Using this information, I applied what I've started calling "the rule of fourths" to my coal loading operations. If one hopper on a mainline unit train represents four hoppers, I can scale down the loading locations in a similar fashion.
My flood-loading unit train operations therefore load 24-25 cars at a time. Those are big operations and trains departing those locations would have coal from one originating point to one destination point. Think of it as one 96-100 car unit train going from loader to power plant.
My medium-sized producers generally load 10-12 cars at a time, which would represent 40-48 cars, a rather significant medium-sized operation in the real world. A mine run with a 24 car limit could therefore work two loadouts and have blocks of coal from several loaders to several different customers.
The small loadouts generally load 2-4 cars at a time, representing 8-16 cars using the "rule of fourths." I hardly ever load less than two cars at a loader just because it doesn't look right to me to just load one car.
When planning your loading operations, try to think of your maximum capacity as half of the length of track you have. If you have 10 feet of track to work with, using five feet of it for a block of cars would allow you to spot empties under the loader and let them be pulled or rolled down from the loader when they are loaded.
Marcus
