Originally published April, 2015.
Our discussion of the Central Avenue interlocking complex in Superior, Wisconsin, concludes this month with a look at how the tower men took direction from the dispatcher. Catch up with part one, here, and part two, here.
Rules, Timetables and Train Control
For many years every railroad had its own rule book with its own interpretation of operating and safety concerns. These were eventually consolidated into a single set of rules and issued to every trainman across the country. These vest-pocket-sized booklets served as each man’s operating catechism. Railroaders couldn’t go to work without them. Use of a consolidated code created widespread understanding of the basic “rights of trains” and how these rights would be maintained from the beginning to the end of each train trip. This was a most-important factor in safe operation of trains. Without these universal rules in place it would be impossible to determine which train had the right to hold the main track while another got out of the way on a siding track.
Most of us are familiar with the format of railroad public timetable (PTT); like their counterparts in airports, they show the arrival and departure times for passenger trains. Those are published for the convenience of fare-paying customers. Railroads also issued employee timetables (ETTs) that showed both passenger and freight train schedules—and more, including the different classes of trains. For example, first class trains were superior to second class trains, third class trains, and extra trains. Second-class trains were superior to opposing third-class trains and to opposing extra trains. Third-class trains were superior only to opposing extra trains. Direction played into it too. Trains of the direction specified in the timetable (usually eastbound) were superior to trains of the same class in the opposite direction. Believe it or not, attention to these simple hierarchies of train classes generally kept all of the famous named-and-numbered trains safely rolling down the line without incident.
When the first timetables were created time itself was an especially vexing issue to overcome. During the nineteenth century every town had its own idea of the current time of day. North American railroads overcame that problem initially by creating their own standard time system. They divided the continent into 144 one-hour segments. Train travel was just a short trip in those days so it actually made sense—then. But soon enough train trips became longer. When trains overlapped these short time zones, accidents occurred. A better solution was needed. The problem of creating a universally accepted standard time was solved at noon on November 18, 1883, when North American railways adopted a system called Railroad Standard Time. It proposed a five-zone system running east to west. In the final analysis a four-zone system was implemented. Although it took many years for this concept to spread, eventually people around the world began using the same timekeeping system. Railroad Standard Time became the world standard—all because there needed to be a way to safely control trains.
The invention of the telegraph added near-real-time communication to key railroad offices. A telegrapher sent messages over the wire to other stations. Those messages were written down by the receiving stations and quickly distributed to everyone required to have them. Division headquarters, depots and interlocking towers were the primary places that used telegraphs until they were replaced by radios and telephones in the 1940s. Computers and microwave tower communication systems were added to the mix in the 1960s. Today, satellites and cellular communication are the dominant technologies.
Signals played a major role too. Train-order signals were used at train-order stations to signal to approaching trains whether or not there was paperwork for them to receive. Interlocking signals protected the crossings and junctions of railroad lines. The interlocking towers controlled just those signals that allowed trains safe passage through the interlocking. And automatic signals installed on the line between different towers provided a way to space out trains safely. These then are the basic components of train control.
While the notion of train control is generally considered to be the signals we see along the tracks, there is an important paper-based component of running trains as well. In fact, trains can’t leave their initial station without the proper paperwork. Train Order Control (TOC) provided the actual written communication issued to train crews at train-order stations (depots and towers). Those train orders spelled out exactly how far each crew had authority to operate its train and what to watch out for along the line. Sometimes the order gave a train authority to just the next train order station down the line where it would receive another order, and so on. A train order must be repeated to ensure accuracy, delivered to those who are to execute it, and expressed in the exact same words to all involved.
For many years, there were two kinds of orders. The “31” order (on yellow tissue paper) had to be signed like the original train order. The “19” order (on green tissue) could be delivered without taking a signature. The “19” order was simply handed up to the front and rear end of a train without a stop. This was usually done with a pair of order hoops (or order forks) on long wooden poles. They could be handed up to passing trains by the depot agent or tower operator, or mounted in a stationary rack next to the track. The engineer of a passing train would grab his orders from the top hoop while the conductor would grab his orders from the bottom hoop as his caboose passed by the train-order station. The time saved by this method of delivery cannot be underestimated as delivery was instantaneous.
Click on “2” for the rest of the story….