Jerry Britton's PRR Middle Division in HO Scale

IMG 4103

Movement of Trains

Following the Sequence of Trains sheet, the LEWIS operator controls movements through the WALL, LEWIS, and JACKS interlockings via a JMRI-based US&S CTC machine, setting routes and signals as appropriate. 

The LEWIS operator maintains telephone communication with the Lewistown Junction yard, coordinating moves between the yard and the main line. 

The LEWIS operator maintains telephone communication with crews on the Lewistown Secondary, Milroy Secondary, and the Selinsgrove Secondary. Movement of trains on these tracks is at restricted speed and is permitted at the discretion of the LEWIS operator. 

Control Disciplines

The LEWIS operator leverages two control disciplines during the course of their duties. 

The discipline governing the main line is “Centralized Traffic Control” ("CTC"; also called “Train Control System” or “TCS”). This means that signals protecting the block by default show “stop”. If the block is safe to enter (meaning that it is unoccupied and there are no turnouts aligned against traffic entering the block from the end a signal is on and the dispatcher has not granted local switching or taken the block out of service) and the dispatcher sets a signal, then one signal will go “non-stop”. All other signals protecting the block remain “stop” because the dispatcher is allowing a train to move through the block in one direction only.

The discipline governing the secondary lines is “Direct Train Control” ("DTC"). This is actually a misnomer because the prototype uses DTC without signals. This selection can eliminate some paperwork on sections of layouts without visible signals. Often the dispatcher will directly control trains by telling the train crew between which points on the layout the train is authorized to operate within. For example, “Train 100, you are cleared from station A to station B”. If the track from station A to station B is defined with multiple blocks and defined to use DTC, the blocks behave like CTC – the dispatcher reserves the route from A to B. However, unlike CTC, the blocks do not return to “idle”. This is to remind the dispatcher that those blocks cannot be given to another train until they have been taken away from the train they were granted to.

Thus, the largest difference in “Control discipline” is how much control the dispatcher has over signals. With CTC and DTC, no signal is “non-stop” without the dispatcher doing something. With ABS or APB, the signals set themselves in response to the trains.