the club layout i’m joining (new to me) uses signals. I’m trying to understand what determines a signal aspect (primarily speed) aside from the fact that the block(s) ahead of a train are occupied.
i can understand why the block preceding an Approach (proceed prepared to stop at next signal) is Approach Medium, but what would cause a signal to be Slow Clear or other aspect?
Speed rating of the switches at the interlocking. Longer switches allow faster speed. Shorter (sharper) switches restrict speed.
And actually the signal preceding an Approach signal would generally be a Clear.* A couple of railroads have special “Advance Approach” indications.
To give further examples:
Consider a crossover with 25MPH (Slow) rated switches.
Any indication for a route through the diverging portion of the switches would be a “Slow …” indication. “Slow Approach” if the next signal is “Stop” (or “Stop and Proceed” or “Restricting”); “Slow Clear” if the next signal is “Approach” or better.
The last signal before the crossover would display “Approach Slow” indicating the speed at the interlocking.
Similarly, an “Approach Medium” signal would be found in advance of an interlocking with higher-speed switched that allows “Medium …” speed indications, rather than in advance of an approach signal.*
Speed signalling basically gives two pieces of information at each signal: What speed to take at this signal, and what speed to be approaching the next signal. It’s not technically about how many blocks are clear ahead, but what indication is the next signal down the line.
Two specific situations, neither of which is likely to apply to a model railroad:
Frequently, in places which have local speed limits for curvature or other reasons a signal will not have a Clear indication. Its least restrictive indication will permit passing it at the local speed limit.
Chuck (Modeling Central Japan in September, 1964 - with, eventually, prototypical signals)
Greg.
What type of signal does your club use? Position light signals are the prototype I am modeling and here is a nice link showing some aspects and meanings. http://www.railroadsignals.us/signals/pl/pl.htm
I should mention that each division had some signals that were unique to that division. Crews would have to qualify for the divisions they run and sometimes interlocking also. Rule books by division would tell you the difference between slow approach and approach medium and so on. I do know that you were absolutely forbidden to go past a stop signal unless you had written permission from the dispatcher.
Pete
Depends a bit on the club layout’s time period. Signals in 1950 weren’t exactly the same as today’s. Just some general rules if this helps…
Block (single head) Signals
Red - Stop. Block ahead occupied
Yellow - Caution. Block ahead is clear, next block occupied. Engineer should slow down enough to be able to stop at next signal if it is still red.
Green - Proceed. Next two blocks are clear. Go whatever the speed limit for that section of track and type of train (passenger or freight) is.
Interlocking (double head) Signals
Green-over-Red. Proceed on mainline
Red-over-Green. Proceed on branchline or alternate main etc.
Red-over-Red. Stop.
On the first two, yellow would indicate the train must slow down prepared to stop, or that the track ahead has a limited speed limit.
Pacific Southern Signal Aspects
the page above explains the signals. I’m trying to understand what track conditions would result in one signal over another.
in general, i recall seeing just a few aspects: Approach, Restricting, Medium Clear. I can’t recall seeing Clear, Approach Medium or Approach Slow. Believe I’ve seen Medium Clear only on a single track mainline leading up through a siding.
I guess on a model railroad, such as the Pacific Southern with at least four trains running at a time, Approach or Restricting are most likely because of another train up ahead, or turnouts needing to be cleared.
Greg.
Nice system. Your club must use speed limits and the speed must be posted on signs near the signals and yard limits. Medium is half the posted speed limit and restricting is speed allowed to stop safely within sight distance. The rule book would give you the most fastest speed allowed in restricted zones. Usually less than 10 MPH. Running by signals is fun unless the dispatcher has clogged the line and all you get is yellows with an occasional red.
Pete
The link you provided shows “speed” signals, there are also “route” signals. Its interesting that a club called the “Pacific Southern” uses the speed signals since the SP, UP, MP and DRGW all used the “route” signals. They both get to about the same place.
Signals give the trains warnings about what speed to use in order to negotiate track configurations or to be prepared to comply with subsequent signals.
The most elementary to understand is the approach signal. It is display in advance of a stop signal. It requires a train exceeding 30 mph to immediately reduce to that speed and be prepared to stop at the next signal. It is preparing the train to be able to stop at the next signal.
Limited speed is typically 40 mph, medium speed is typically 30 mph and low speed is 15-20 mph.
The signals with a speed associated slow the train down to the correct speed to pass through the trackage or switches. If the turnout has a 30 mph speed restriction and there were no other limitations, then the signal would display a medium clear. That would get the train down to the proper speed.
The advance approach (route) and approach medium (speed) are signals that slow high speed trains down to a lower speed so they will be able to comply with a restrictive proceed indication at the next signal.
A train going 70 mph will encounter an advance approach which slows it down to 40 mph in preparation to encounter an approach or diverging approach signal which have restrictions of 30 mph associated with them. Not having the advance approach would require the 70 mph train to drop down to 30 and be prepared to stop at the next signal in as little as 2 miles, which might no be safe. Using the advance approach allows the train to slow over 4 miles or so.
Many switches have slow speeds through the turnouts. #9, 10 and 11 turnouts may be restricted to 15-20 mph and #14-16 turnouts may
Because of short distances and complexity, most model signalling systems, even on a large layout, don’t follow prototype logic. So it’s hard for anyone else to tell you exactly how that layout is doing detection and presenting signals. The folks who built and maintain that particular system would be the best source.
On any layout that I operate on that has signals, I use a simplified logic:
If the signals is green - you may proceed.
If the signal is red - stop.
If the signal is yellow - slow down.
If the signal is any other color or group of colors - slow down.
That pretty well sums up model systems. Since there is not a real good way to determine a model train’s speed and unless the momentum is cranked way up, stopping in time is not a problem.
I would add that if you get any yellow watch out for the next signal.
At most clubs I been a member of that use signals it was rather straight basic signaling.
Red=stop
Yellow=proceed to the next block at reduce scale speed.
Yellow over yellow= diverging route such as going into a passing siding.Proceed at slow scale speed prepared to stop at next signal.
Green=Clear proceed at scale track speed.
Triple yellow=proceed at the slowest scale speed prepared to stop on hand signal.
This was used for entering the yard or passenger terminal…The YM or passenger terminal operator gave the stop hand signal when you was clear.
after looking at the clubs signals, i’ve organized them in my head as follows
for me, understanding what the signals indicate and that the following block may not be cleared allows me to plan ahead. I can slow down knowing that i’d have to stop anyway. Or in at least one case, alert the tower operator to clear the route and signals before i get there.
While this is all new to me, i don’t recall reading much at all about operations using signals like this. Once i’m given a train, i shouldn’t have to talk to anyone to get it to its destination. But of course, things don’t always work out, and that’s when things become entertaining !
A “slow clear” is a clear signal that must be taken at slow speed. You would usually find on a slow speed switch when taking a diverging or converging route. Once the train is clear of the spring switch or interlocking MAS (maximum authorized speed) then applies the same way as if the train had past a clear signal.
The speed is determine by the rule book for the specific railroad. On the GFSM where I operate. Green = 20 smph for normal trains 30 smph for passenger and priority trains. Yellow is reduced speed or 10/15 smph respectively. Red flashing is (after a full stop) a speed such that one can stop with in 50 feet.
Other things cause a signal.
These things would absolutely not affect signal indications unless enough damage has been done to the track to cause a rail break, or the track is protected by something like a slide detector fence. This would simply cause the signal system to treat the block as “occupied” and give an appropriate indication.
If a section of track has been bad orded, trains will have bulletin instructions from the dispatcher for slow orders at specific places. The signals will display whatever indications they normally display. The dispatcher does NOT set the speed on the signals. The dispatcher just clears a route and the signal system determines the correct indication to be displayed. This is essentially hardwired into the signal location and is not configurable based on current weather or track conditions.
Any of these would simply show the block that the other train is in as “occupied” and the system handles it accordingly. There is absolutely nothing special or different about any of these cases. (And in the case of no. 1, if the train is switching completely clear of any signaled tracks, then th
That’s probably a pretty good, simple set of signal rules for a model railroad, but it should be clear that’s not typical of prototype rules.
Note that in any prototype rulebook, a “Clear” signal implies nothing about speed. It’s just clear. Speed limits for the line (including any permanent slow orders) would be listed in the employee timetable.
Signals that require a reduction in speed (like “Slow Clear” etc.) apply equally to any train of any type or priority.
This is actually reasonably close to prototype.
To clarify your third point though, note that yellow on top normally represents approach signals; it tells you the speed at the next signal.
Typical aspects in most 3-color speed signaled systems:
Yellow over Red (or just yellow on a single head) - Approach [next signal Stop]
Yellow over Yellow - Approach Slow
Yellow over Green - Approach Medium
The Book of Rules & the Employee Timetable.