I wired my layout with multiple cab control on separate control panels for different sections of the layout. I can run a continuous train, with other operators running staging trains separately on different parts of the layout. The layout is wired so that the main control panel can operate trains on any part of the layout, including the upper level.
Marlon
See pictures of the Clinton-Golden Valley RR
I built several DC cab control powered layouts before I finally tried DCC. None of these layouts were very big and I usually operated alone. Trying to "run" two trains by myself usually meant just running two trains around the layout while I performed the "toggle switch two-step" to keep them from running into one another. While visitors were impressed that I could run two trains, I was not able to teach a second operator how to take over one of the trains using the cab control system. Part of the problem was that I used a central control panel with Atlas components layed out in straight lines. Having to match the component number to a numbered block of rail often took longer than it took the train to travel that block with obvious results. DCC made all of this so much easier and more fun, too! DCC wiring is much simpler as well.
Hornblower
It depends on what you consider "operating" as well. Is the operator, to use John Armstrong's terms, the "Spectator", the "Engineer", or the "Dispatcher"?
A "Spectator" layout with lots of automation (and a dispatcher) can support a very high density of trains. What is being sought is the sight of a train or trains going through a scene or scenes. DCC is not all that helpful for high density operations because of its "see and avoid" mentality.
A "Dispatcher" layout can also be high density (to make the Dispatcher work). But again, high density of trains on track requires not just engine control, but track control and blocks. Just like prototype light rail systems.
An "Engineer" layout tends to be lower density, with number of trains limited by passing tracks or other temporary "get off the main" devices. Without a dispatcher and some kind of operating rules, density has to be limited to practice "see and avoid". Direct engine control via DCC or similar supports the Engineer experience. Meets and passing are arranged between the engineers for the 2 trains.
It's been interesting to operate a large modular HOn3 single track layout. Operations in Engineer mode (which most of us prefer) can quickly grind to a halt if train density gets too high. Spectator operations can go to a higher density because all the engineers are just running a train for show. The density could go even higher with some run rules and a dispatcher coordinating.
Fred W
Thought some more about the original question. I think the underlying question is, "How does one achieve the maximum train density on a given layout?" And what are the limiting factors?
I thought the history of the prototype might give some answers. Railroad infrastructure - land, roadbed, track, maintenance, people, buildings - is very expensive. The best way to get a profitable return is to maximize density on limited infrastructure. Railroads have been working on this for over 150 years. Model railroads are very similar in this regard - infrastructure (the layout) is expensive in terms of space, time, maintenance, and costs. Time, maintenance, and costs are non-linear - they go up as the square of the space. Space for model railroading and land for railroads is generally hard limited - there is a gigantic step increase in cost to go above what is on hand.
Narrow gauge was an attempt to reduce cost of infrastructure to a greater degree than the capacity. It failed.
But the right answer proved to be increasing density of trains (increasing capacity) on a limited infrastructure.
Early railroads were a "see and avoid" solution. The engineer was responsible for not crashing into another train. Very much how a DCC layout operates today.
The next step was the addition of timetables and operating rules to assist the engineer. This allowed a substantial decrease in following distances for trains, and prearranged meets reduced waiting times. Both helped to dramatically increase train density. But limited communications didn't really allow for centralized dispatcher control, and therefore things would fall apart when somebody got significantly behind schedule. Happens all the time in model railroad operations.
As communications improved, trains could be run even closer together as long as the dispatcher could control the track. Signalling systems and station/train position reporting gave the dispatcher command and status respectively. There are some model railroads that reach this point.
In modern railroading, blocks have become shorter and status is reported on a full-time basis to the dispatcher to allow the dispatcher even tighter control and the closest practical train spacing for a given track arrangement. Algorithms have been written to allow computerized dispatching. And so even greater train density has been achieved.
The density gains in the late 20th Century have been so great that most of the double track from the early part of the century has disappeared.
just my thoughts
fwrightThought some more about the original question. I think the underlying question is, "How does one achieve the maximum train density on a given layout?" And what are the limiting factors?
On my layout, well it's only plywood wired and ready for track--but I can see it all operating in my head. You can run 4 trains, all of them working. There is a yard switcher, a lumber switcher moving boxcars to fill orders, there is a mainline train, either freight or passenger, and the freight drops off and picks up cars, and there is the logging train coming out of the mountains to drop logs at the mill.
The limitation is space. It's roughly 8x12 and eventually everyone will need to be in the same place in the center at once. Practically speaking, two operators can work at once.
Chip
Building the Rock Ridge Railroad with the slowest construction crew west of the Pecos.
On a single track mainline, with passing sidings, and two way traffic. The answer is a train can onlu move if it has an empty track in front of it, and an empty track to stop on.
If you had both tracks at each passing position occupied, with one east bound and one west bound train at each, then all east bound trains could move up one siding, and then all westbound move up one siding. Great care needed, and very boring.