Which signaling or track control method is preferred and why: CTC/warrants/other? What are advantages and disadvantages of each? Are there places where one would work better than the other?
It depends on the application. If you are talking high density mainline then 2MT CTC would probably be best. If you are talking branch with 1 or less trains a day then TWC, DTC or block register would probably be fine. If you are talking a coal conveyor line or commuter line running streetcar style then rule 251 doubletrack ABS might be best. You have to consider a lot of things includeing capital costs and onging maintainance cost for signal systems also.
Is it easy to switch from one to another and what would prompt such a switch?
Easy? I’ll leave that to the experts.
As to why change.
An example would be the BNSF upgradeing the western end of the transcon from DT ABS to 2MT CTC. It increased capacity. Cheaper then adding another track.
Essentialy CTC is ABS with controll points at the sideings and diverging tracks. The intermidiate signals act just like ABS.
The main difference is ABS is a protective overlay and does not grant authority, while in CTC the signals do give authority. In ABS territory there is always another method of granting authority like DTC, TWC or rule 251 directional running.
Great answers and thanks Chad. I’ve always wanted to know more about signals and how they function. The ‘why’ is pretty easy to figure out!
Upgrading signal systems/train control methods is always expensive. Such projects are usually postponed until they become economic necessities, as opposed to something it would be nice to have.
Mac
The most versatile is Rule 261 CTC, track signaled in both directions (or 2MT to you GCOR folks). This offers the greatest traffic density, but is also the most costly installation. A less expensive version is Rule 251 CTC, track signaled in one direction. Works great if all the traffic moves in the same direction, but movements “again the current” generally require a track warrant of some sort.
The least expensive is non-signaled track warrants, ie Dark Territory. Simple to use, but doesn’t support high traffic densities. Warrants involve a great deal of communication with the dispatcher. Most rule books don’t allow one train into another’s warrant, until said warrant is canceled. So only one train operate on a given piece of railroad at a time. However, warrants often offer the greatest flexibility of movement for a train. You can be given permission to move in any direction, at any time, between the two end points of the warrant, until you report in the clear.
Control systems will be upgraded if rising traffic levels warrant it. Likewise control systems can be downgraded, due to falling traffic levels. Upgrading control systems is rarely “easy”.
Nick