Living in a fairly large metropolitan area, I have had my fair contact with freight trains. There is a very busy track running a few hundred yards behind my house. Noticing that the trains in the area have a speed limit of 48 MPH and seem to run in both directions, I have been trying to get some information on how the rail switching system works. For instance, I can recall recently that I heard a fast-moving rather lengthy freight train heading east along the single track behind my house, and not 30 minutes later, there was another heading along the same track heading west. I was wondering if anyone could either provide a link or some information as to how these trains avoid head-on collisions and can operate on the same track safely? As a five-year veteran of the internet, I have tried several search engines in different formats with mimimal success. Can anyone satiate my curiosity?
One possibility is that the train line near you leads into a Y junction. Consider the eastbound trains as going from the foot of the wye then up and to the right branch while the westbound trains come from the left hand branch of the wye and go opposite way.
Another possibility is that there is a siding somewhere near where you live where trains going in one direction get off in order to allow trains going in the opposite direction to pass.
Keeping trains from crashing into each other may not be as ‘sexy’ as keeping planes from crashing into each other but it is the same general idea. Typically a single company owns a section of track and its central dispatch office strictly controls when and how fast trains can travel across it. I imagine those little boxes that they put on the last car in a train these days instead of a caboose has electronics that send back send and location data to the central dispatch office, thus making sure all trains are in their proper location.
From Military text describing train activities and dispatching.
This site also provides forms and descriptions of other operating procedures.
"SINGLE-TRACK, DOUBLE-TRACK, AND MULTIPLE-TRACK OPERATIONS
4-9. A main track may consist of a single track or two or more tracks upon any of which the current of traffic may run in either direction. The three types of main track operations are discussed below.
SINGLE-TRACK OPERATION
4-10. In a single-track operation, dispatching is carried out by written train orders. A first-class train depends on the timetable schedule for its authorization. When leaving the starting terminal, the crew is authorized to travel along the route according to the established timetable schedule. On a single-track line, the timetable specifies the superior direction. Therefore, a first-class train traveling in the superior direction would be superior to all other trains on the line. Inferior trains must clear the main track completely by going into a siding or yard and line the switch for the main track. In no way should the arrival of the first-class train be delayed.
DOUBLE-TRACK OPERATION
4-11. In a double-track operation, each track is designated a direction of traffic specified by timetable. No deviation by crews is allowed without specific orders from the dispatcher. The dispatcher must continue to ensure that inferior and superior trains do not meet and that opposing trains are separated. Although double-track operations are simpler than single-track operations, the density of traffic is generally two or three times greater than on a single line. Most double-track lines are equipped with automatic block signals. These signals require the dispatcher to space the trains so that neither of them are hindered by the reduce-speed and stop signals of the train ahead. Proper train spacing is a delicate phase of dispatching. Too much starting and stopping results from trains being too close together.
MULTIPLE-TRACK OPERATION
4-12. Multiple-track systems are rare in military operations. Since towers (as directed by the dispatcher) control movement, the dispatcher determines the flow of traffic for each train in order to provide greater movement flexibility and track use. On three- and four-track systems, the operating problems are even further reduced. Four tracks are ideal because they can provide high- and low-speed tracks in both directions. High-speed tracks are usually on the outside to permit passenger trains to load at stations. These tracks are often thought to be reserved for passenger trains only. However, express trains and fast freights can use them providing they can make passenger-train running time. The flow of traffic can be more rigidly enforced on a four-track system because there are two tracks running in each direction."
The line mentioned in the OP is most likely equipped with a form of Centralized Traffic Control (CTC), allowing bi-directional movement on a double- or multi-track line. Dispatchers working in a central dispatching station remotely grant movement permissions and control crossover switches out on the line, while the signals mainly operate automatically. The dispatching location may be hundreds of miles distant; for example, CSX Corp. dispatches trains on the bulk of its lines, covering much of the eastern half of the country, from Jacksonville, FL.
Train frequency depends on average train length, maximum speeds allowed, and the length of signalling ‘blocks’, which can range from less than one to several miles. A typical double-track, CTC-equipped freight line can handle up to about fifty movements per day at any given point along the line. A passenger-oriented double-track line, with shorter, faster trains, can handle more. Some multi-tracked locations with heavy passenger service see hundreds of movements per day.
I’ve posted this link before, but a good summary of US rail signalling practices has been published here:
http://www.trainweb.org/railwaytechnical/US-sig.html
Cheers,