In a comment to that post, Jeff Aley made some additional points. With Jeff’s permission, I want to develop those, because they are important in model railroad operation. Here is his first point:
“I think there's one additional objective for the CC&WB. In systems
where a Car Card is mated to a Waybill, the system serves as a means
to track shipper's demands for cars, and the subsequent delivery
of loaded cars to consignees.”
This is quite true, and any system for car movement on a layout needs to do exactly what Jeff describes. It need not be a car card-waybill combination (what Jeff refers to a CC&WB), but can be any of several systems.
For my layout operating sessions, I create an “Actions” list for all industries, though some of them will have no cars at them, and others will have cars at them that don’t move. The point is that I know what is going to happen at every one of them. Here is just the Shumala part of such a list. (You can click on the image to enlarge it.)
Note that I contemplate two cycles of work, though only the first one is shown above, and for each cycle, I list what the starting point will be, and what action takes place in each cycle.
This kind of planning is one way to address car movement cycles. The general problem of car cycles, that is, the patterns of car movement over a series of operating sessions, is a real one. It isn’t solved directly by waybills, nor directly by any CC&WB system, though of course something like a four-cycle waybill does direct four cycles (and why stop at four?). There has to also be a tracking process, unless you stack multiples of four-cycle bills into a car-card holder.
I keep track of what cars go to what industries with what I call a “pairs list.” This is just a list of all industries and the waybills which exist for cars going to or coming from that industry. I’ve described the construction and use of such lists in a couple of posts. The first of these posts is a topic introduction, and it is here: https://modelingthesp.blogspot.com/2012/02/waybills-17-pairs-list.html . I have followed that up in several places, perhaps most usefully in this one: https://modelingthesp.blogspot.com/2017/03/waybills-part-58-more-on-managing-bills.html .
Jeff also made a second point, related to the first. Here is his statement:
“The system may also implement the home routing of empties.”
Here of course we recognize that both prototypical model waybills, and most CC&WB systems, readily accept an additional Empty Car Bill in a sleeve, or empty cycles on the four-cycle bill. The question, though, may be routing, and this is what I think Jeff means. If you model a railroad in the center of the United States, homeward empties may go in all directions, and you need a way to correctly move them, assuming of course that you wish to follow the Car Service Rules in most cases.
There are a number of versions of Empty Car Bills out there, as I have identified in several posts (you can use the Search Box at upper right of this post to search using “Empty Car Bill” as the search term). Hopefully most people want to do better than something like this, where one simply removes the waybill:
As Jeff pointed out, the drawback to switchlist systems is that you don’t immediately know where a car should go for the next operating session. On my layout, it isn’t an issue since most outbound cars return to storage (I have way too many cars for my layout, which has the good point that there is lots of variety among operating sessions, but obviously the drawback of repeated car handling.) But in any case, I dislike the idea that we program long series of car movements. I generally only program two: loaded and empty.
On Otis McGee’s layout, partly on account of the complications of dividing northward (railroad east) trains at Dunsmuir for movement over either the Siskiyou or Cascade Mountains, there need to be more waybills in a certain fraction of the car sleeves to permit variety. I described this problem and the current solution to it in one of my waybill posts (you can find it here: https://modelingthesp.blogspot.com/2012/04/waybills-21-understanding-waybill.html ). This applies to the selection of both loaded and empty paperwork, as it has to apply to either route.
I thank Jeff Aley again for raising what I think are significant points about the use of waybill systems for layout operation. (Of course, I may not be addressing the points that Jeff actually intended to make . . . if so, I hope he will respond.) Maintaining realistic car movement in an ongoing series of operating sessions is an interesting challenge, and there are a variety of ways to approach the problem.