One thing that has been constant since the early days of railroading is that a dispatcher controls the flow of traffic between interlockings. An interlocking is simply an intersection or union of two or more tracks. An interlocking is more than a section of railroad with multiple tracks in a busy mountain district or a crossing of railroads. It can be as simple as a passing track alongside the mainline, a branch leaving the main, or as complicated as a flyover junction with an interchange track.
When trains were run with timetables and train orders, the dispatcher would arrange meets at sidings and give permission to trains to proceed to different areas. The local operators would telegraph or telephone the dispatcher and tell him, or “OS,” the location of the train. I have heard many different meanings for “OS,” but I like the definition “on the sheet.” The dispatcher had a sheet on the table in front of him with the station names, sidings, and other interlockings down the center. Trains were noted across the top on either side of the column with the location names. On one side would be the trains headed east or north and on the other the ones headed west or south. The dispatcher would write the time that the train is OSed on the sheet at the particular location which called in the train’s location.
When technology advanced, and dispatchers received CTC, the dispatcher still controlled only the interlockings. The areas between the interlockings were controlled by automatic block signaling, or ABS. Automatic block signals control traffic by spacing the trains for safety. If a train is overtaking a slower train, the quicker train will run into a yellow restricting the speed of the faster train. If it were to continue to overtake the slower train even at the restricted speed, then the faster train would next come to a red signal. The sole reason for ABS is to keep a minimum safe distance between trains. When the dispatcher changes a signal at an interlocking in order to allow one train to enter a siding so that another could pass, the ABS signal would change to either red or yellow to keep any train following from crashing into the stopped train or hitting the oncoming train.
Under track warrant control, the dispatcher gives a section of track to the train and he can then establish meets at the interlockings. If ABS is still available, it will continue to serve the same function as noted above. If the territory is dark (unsignaled), then the dispatcher still controls the interlockings in that the train crew will go from interlocking to interlocking and the train crew can throw the switches all according to the directions the crew will get from the dispatcher.
As you can see, the role of the dispatcher is to control trains within interlockings. And to prove the rule, here is the exception. In complex interlockings with tower operators, the dispatcher would designate to the tower operator the track on which the train would approach the interlocking and the track on which the train would exit the interlocking. Within the bounds of the more complex interlocking,the operator has discretion on how best to route the train, helpers and other traffic.
The next time you look at your railroad and are thinking about your dispatching panel, remember how the prototypes work their dispatchers. The dispatcher needs to have a board representing the section of track he will control. This can be as simple as a steel sheet with the track plan on it. Magnets can represent the trains and you can write on the magnet with erasable ink markers. You could set up a panel which looks more like the CTC panel of old or you could even use computers to simulate the track plan just as the prototype does today. You can set up the panel to show the interlockings but the distance between the interlockings does not and usually is not proportional to the distance the train will travel. The dispatcher will just have to become more aware of the distances between interlockings and the time the train will take to cover that distance.
When you set up your railroad and your dispatcher, remember the control the dispatcher has. Modeling this aspect can be both fun and a challenge.
Until the next time, I hope all the signals you see are green over red.