Yard Operations and other questions

[BoilerBob]

What happens in a hump yard when the particular track gets full? Do they put the cars on another track then make up the train later? Which brings me to another question.
What governs the length of a train? Is it motive power, state law or something else?

[ExCon90]

As to the second question, a lot depends on management policy: trains as long as the available motive power can pull vs. shorter trains on regular schedules. Both policies can be in effect on the same railroad for different types of traffic; i.e., whether the traffic is high-paying and must be moved on schedule or is lower-rated and can afford to wait until enough tonnage is available to make up a longer train. Other constraints on train length may be the length of the shortest siding on the route, or the ruling gradient over the route, or how much motive power is on hand and ready at the time. In times of economic downturn there is often a tendency to run longer and fewer trains, but this can be counterproductive if it significantly lengthens transit time, thus reducing efficiency in the use of equipment. I'm not aware of any State laws governing train length, although there have been laws requiring additional crew members on longer trains (a number of states had so-called "full-crew laws" requiring an extra brakeman on all freight trains regardless of length); this often resulted in a brakeman, called a "swing man," boarding a train at a state line and leaving it at the next state line to wait for a train back.

[Engineer Spike]

Lots of times a train is made up of several blocks of cars. Some of these may be set out along the way. Other times, they are for ease of switching down the road. For example, tonight I will take a train out of a large yard, although it is no longer a hump. There will likely be two blocks for set outs on my run. One is for an outlaying local, and the other is a shortline interchange. The rest of the cars may be blocked or not, based on yard capacities, and management's plan. These may be blocked for local cars, and several foreign carriers, at our destination.

Most times the classification track will not hold an entire train. Each block may occupy a separate classification track. The tracks are doubled together so the blocks are in the proper order. These are then pulled to the departure yard. If one classification exceeds the track length, the yardmaster may either have the first bunch taken to the departure yard, or start building up on another track, depending on how many other classifications he had going on then. Basically whether or not he had another free track.

ExCon has pretty well answered the second part. There are certain metrics which a railroad measures its performance. One it the dwell time, which a car stays in the yard. The other is how big a train is most efficient to run. Here there are conflicting points of view. A short train may not cover the cost of fuel, locomotive usage, and crew cost. A long train may cover the costs, but be slower. A 25 mph curve will take longer to slow down to, longer to traverse, and longer to accelerate out of. The destination yard may not be able to handle it. A set out may take longer, since the air may take longer to recharge, after getting back together. Any grades may limit the weight. This can sometimes be overcome by using mid train remote controlled units, since there is a limit of how much power can be on the head end.

Some short trains are run. This may be advantageous if the yard is running at capacity, and room is needed. Customer service is enhanced by quick delivery. In short, there is no rule. Many factors come into play.