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Signalogic Systems
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Before teaching I worked for Canadian Pacific Railway. It was interesting since
I've been a railfan long before that. I love trains but my specific interests
are in signalling and control systems. I worked in the control-systems group at CPR
developing an OCS (Occupancy Control System) based on CROR (Canadian Railway Operating
Rules). While at the rail I held an 'A' rules card.
Although I do not currently have a layout, I enjoy model railroading, especially the control-system aspect. In the future I am planning on expanding this page to include several planned model railroading projects including signalling systems based on PIC processors which accurately reflect CROR (Canadian) prototype operation. The system will use single-twisted pair RS-485 communications between processors to convey information about block occupancy and signal indications. Other planned projects include a DCC receiver and DCC throttle with a Win-32 PC front-end (already in-progress).
CROR Signals
CROR (Canadian Rail Operating Rules) specifies, among other things, signal indications and procedures to govern train movements. Application of these rules are outlined below and are taken from the CROR rules dated 1990 (the latest 'red book'). Note that CROR specifies signals for searchlight type colour light and semaphore signals only: other types are not used in Canada (In fact, you'll hardly find semaphores anymore). Canadian railroads traditionally use single-head type searchlight signals (where one head can display three aspects by using colour filters). These signals have the advantage of excellent alignment however are mechanically complex and so are more expensive and prone to mechanical failure. Beginning in the late 90's newer applications on CN mainlines began to use three-lamp type signal heads. Indications given by each are identical and CROR rules regarding 'dummy red' aspects as well as head placement on a pole still hold true.A Few Practical Notes On Application Of Signals In Canada ...
Note that many of the practical notes will apply to high-density rail areas in Canada but may not reflect the 'norm' for sparse areas in western Canada where long runs are found (This is fine for one who is using the CROR system as a prototype for modelling since most model railroads will not have long scaled blocks anyway). Many of my personal observations were made while working for CP rail and while commuting to work on the GO commuter train which runs on CN and CP lines in the golden horseshoe area of Ontario (the area surrounding lake Ontario on the east side). This is a populated, high-density rail area with twin main-lines. There are a large number of sidings on these lines which service local industries.As well as personal observations I have had a few discussions with other enthusiasts regarding signalling (For example Kevin from Signalogic Systems) and so I have made a few corrections and clarifictions along the way. Bear in mind that the approach of this page is to outline signalling as it would apply to a model railroader. Although many signals in high-density areas are centrally-controlled by what is called CTC (A computerized central traffic control system in which displatchers, with the aid of a computer system, control routes) the aproach I want to take is one of fully-automated signals for a model layout which accurately reflect indications based on train movements. For that reason, most of what is outlined here is based on an ABS (Automatic Block Signalling) system even though many of the prototypical examples would indeed be CTC signals.
Almost all signals in Canada pre-1990 are single-lens searchlight signals and normally you'd find signals arranged as one, two or three aspects (heads) mounted on a single mast. CROR Signals are designed in principle to display speed information only - how fast the engineer may proceed now and approaching the next signal. More complex signals (e.g. three heads) can display a wider variety of speeds. On a high-speed mainline, a single-head signal is sufficient to display all necessary speed information (i.e. full speed or prepare to stop) however where switches are involved such as a crossover to another line, two or more heads may be required to display the fact that the engineer may have to slow to medium or limited speed to pass the switches before continuing.
For the modeller, by extrapolation signals also indicate when a turnout is to be taken - or rather would warn the locomotive engineer of this by way of indication. The typical example of this is an indication warning that a turnout can only be taken at some particular speed while a mainline can be taken at full speed. An accurate model of the prototype would dictate that signals (at least CROR-compliant ones) must indicate not only the status of blocks ahead (clear or occupied) but also be aware of turnout positions ahead to indicate the maximum speed such switches can be taken. If, in a layout, a turnout is known to take a certain scale speed (we've all had switches on a layout which can't be taken at full speed just like the prototypes) the signal should indicate that speed accurately as opposed to simply 'full speed'. Of course, where a block ahead is occupied on the route to be taken (straight through or diverging) the signal must indicate that, too! This also dictates that a microcontroller is likely required to perform the required logic to make accurate indications.
Physical Signals
Under CROR a normal single-head signal (one which can display only a single aspect) can only display a 'Stop and Proceed' aspect as it's most restrictive indication. This is often used where a train is to enter dark territory which is not signalled (e.g. a territory where an OCS system is used exclusively to control train movements). To make that indication more restrictive (i.e. Absolute stop) the signal must be fitted with an 'A' plate. This might be the case, in theory, where a signal is protecting an interlocking (although, as we shall see be example, two head signals are more frequently used for such purposes). This is not true for dwarf signals (such as those used in switching yards and terminals) where a single red aspect indicates 'Absolute Stop'. This is logical since such signals usually protect a line entering another route at a a switch ... places like Union station in Toronto or in Fort Erie near the railway bridge to USA are littered with dwarf signals.Being a high-density area where high-speeds are usually not possible (i.e. few long runs), there aren't many single head signals in the Niagara area (Local Note: One of the few visible ones is on the line which runs E-W under Glendale Avenue near Dennis Morris in St. Catharines). In my area there aren't many 'long runs' - essentially all runs are approaches to an interlocking - and so you'll find mostly two head, staggered signals used. Two-head signals can indicate a variety of speeds at which the train should approach the next signal. As an example consider a two-head signal protecting a crossover switch from one track to another, the train must be moving no more than the medium or limited speed that the switch is rated for. The aspect required to do this is Clear-To-Medium, or Clear-To-Limited. Both aspects require the Yellow over Green aspect and thus two heads on the signal mast. (Local Note: take a look at the lines crossing Lundy's lane where it is a single lane in Niagara Falls or running near Lyon's creek/Townline tunnel in Welland and you'll see two head signals on single track).
Under CROR, where a signal has two heads, the most restrictive signal displayed depends on the position of the heads on the mast.
If both heads are on the same side of the mast
(one directly under the other), a 'double red' indicates Absolute Stop however if the heads are on opposite sides of the mast (staggered) a 'double red' indicates 'Stop and Proceed'. A popular modification to signals is the addition of a lower 'dummy red' aspect rather than an 'A' plate - not required in theory but certainly done in practice in this area. The reasons are obvious when a snowstorm hits - a plate is easily missed but a glowing lamp is easily seen.
(Local Note: While on the 406 through St. Catharines heading North check the signals on the right side of the CN overpass - the line which runs to Thorold and over the canal.
Each signal has two heads: the top one with three separate lamps - new style - and the lower aspect a single, fixed red aspect. This allows the signal to indicate absolute
stop: a good idea if the bridge over the canal is up!).
Three head signals always have all three aligned on the same side of the mast
and always indicate the more restrictive indication of 'Absolute Stop'.
Three head signals, which indicate a wider variety of speeds at which a train must pass through turnouts, are frequently found on lines where a siding and turnouts are present (e.g. At a switch before a diverging route). (Local Note: You'll find three head signals
everywhere but a really neat example is in Niagara Falls on Stanley Ave. near Thorold
Stone Rd. where four rail lines meet in a massive interlocking before the yards there - three head signals allow a wide variety of speeds through the interlocking to be indicated).
A few Photos showing a typical interlocking. This one is in Fort Erie, Ontario, where CN mainlines diverge before crossing the Niagara river to the USA. A variety of speeds may need to e indicated here based on the route taken - the single line here diverges into three separate lines and the speed over which a train may pass through the two consecutive switches depends on the route aligned.
A head-on shot showing the tracks diverging. A signal bridge is visible in the background.
A side shot
Another side shot showing a few more details including the housing for the controller.
Newer signals (installed in the late 1990s) on many CN lines are simpler colour-light signals with two or three lenses. This signal, located on the CN lakeshore lines running through Ontario street in Beamsville, has a single head for southbound trains and two heads for northbound trains. Note the 'R' plate allowing a train to proceed at restricted speed on a red signal.
Large shot of the signal showing details
A side shot
A close-up of the signal heads
CROR signal indications
Unlike many European signals, in Canada you will never find a 'double green' signal. Indeed the most permissive signal is 'green over red' (Clear - 405). Where a signal has two or three aspects shown, red is used as a 'placeholder' so that a 'green over red' signal on a dual-head is the same as a single green aspect on a single-head signal (the most permissive indication). A quick look at two and three head signal indications on the accompanying images detailing signal indications verifies this rule.
CROR Signal Indications Rules 405 through 408A
CROR Signal Indications Rules 409 through 415
CROR Signal Indications Rules 416 through 422
CROR Signal Indications Rules 423 through 430
The CROR system is unique because (i) the most restrictive indication depends on the configuration of the signal heads (i.e. which side of the mast each signal head is mounted-on) on the mast, (ii) A single head signal cannot display an absolute stop indication without an 'A' plate (or more commonly the addition of a second aspect making it a two-aspect signal which can display a restrictive signal) and (iii) because it features a blinking indication (some European systems also feature blinking signal aspects). The best example justifying the blinking signal is a single-head signal protecting a block. A system which supports only 3 indications can indicate the presence of a train ahead in the next two blocks only. If the protected block ahead is occupied the signal indicates RED, if the block ahead is clear but the following block is occupied the signal indicates YELLOW. If the next two blocks (including the one protected by this signal) are clear, a GREEN indication appears. With CROR, a signal can indicate the occupation of the next three blocks by indicating RED, Blinking-YELLOW, YELLOW, and GREEN. This allows more advanced warning of a train ahead, especially important in low-density areas with very long blocks and very long trains such as in western Canada where a train hauling grain can stretch well over a mile in length! Advance warning here means better control of train speed (i.e. not having to hit the brakes as hard :). The CROR system was designed specifically for Canadian terrain (which varies from long blocks in the praries to incredibly dense lines in the South).
Modelling the CROR System
The CROR system is unique in that the position of the signal heads on the mast confers the type of indication. The application here is how a 'double red' is interpreted as either 'Absolute stop' or 'Stop and proceed'. One of the other unique points of CROR system is the application of a blinking yellow for an advance signal so that instead of showing simply three indications, a single head can indicate four (As well, there is a blinking green aspect so really we've got five indications possible).
On Long Consecutive Blocks single head signals are used (local example: in St. Catharines at the Glendale avenue overpass near Burgoyne Woods). These signals essentially indicate the occupation status of blocks ahead. In a model layout there will likely be few of these since the density of most layouts (similar to the region where I live) does not allow for too many long blocks.
Approaching an Interlocking you'll usually find two-head staggered signals which indicate the speed with which the next block should be approached. Staggered signals allow a train to stop and then proceed at restricted speed. A two-head signal can indicate slow speed as may be required to pass through a turnout with a tight radius. It may also be used to protect a siding entering a mainline and can indicate that the train must pass through the switch slowly until clear of it.
Interlockings and Junctions are protected by a two or three-head signal depending on the speed indication required (Where these are not staggered and all heads are on the same side of the mast). Most CTC systems in a high-density area would employ a two-head signal for high-speed switches such as crossovers between high-speed rail lines and three-head signals for more complex interlockings (e.g. the one at Fort Erie above where one main line diverges into three lines). For the modeller, the lower head of a three-head signal is usually red anyway so this simplifies design should a three-head signal be desired. The same may be true with two-head signals whereby the lower aspect can be fixed red for a main line (indeed this is done in prototypical situations like that described on the local note above in which a dummy red is used for the lower signal head).
NOTE on two and three-head signals: When modelling most U.S. railroad signals it is
usually the convention that the top head indicates the status of the main line while
the middle (or lower) head indicates the status of the siding. If a switch is
aligned for the main line the lower head goes red so the possible indications would
be G/R, Y/R, or R/R. If the switch is aligned for the siding the possible indications
are R/G, R/Y, or R/R (with R/G usually not indicated unless it is a high-speed siding).
Under CROR rules the first three indications (G/R, Y/R, R/R) are compatible although
there are many others possible that the modeller may or may not want to indicate.
The 'siding' indication R/Y, however, does not exist! The correct CROR indication
would be red over blinking yellow (rule 425).
Due to complexities with CROR indications it is apparent that an intelligent controller
(such as a Microchip PIC processor) is required to model the prototypes correctly!
At a Siding a two-head signal is usually used allowing indication of speed to pass the turnout (in a limited manner - only a few indications are possible dictating the speed through turnouts including 421 and 425). With both heads on the same side of the mast this signal can indicate 'absolute stop' to a train approaching a misaligned track switch. Also possible is a three-head signal depending on the speeds which must be indicated (i.e. if the switch can be taken a medium speed which a two-head signal cannot show). If the track is within or, more often, exiting a Yard a single-head dwarf signal is often used (Where 'red' is always absolute anyway). To make matters confusing, I have often seen on the CN mainline three-head dwaf signals where the top two lamps were fixed red and only the lower one changed colour. That certainly renders unambiguous indications however seems like overkill, especially to a modeller.
Modelling Examples
In the above example we have a single track (high speed main line) and a signalled siding. This is typical of what you'd find along the CN lakeshore lines where the main line is multi-track, high speed and is signalled via bridges above the tracks. Sidings are industrial spurs which service many industries along those lines. The siding is protected from entering the main line by a dwarf signal. The dwarf is a good choice since it can assert a rule 429 (absolute stop) indication. The main line could be a two or three head signal. Usually, at a major interlocking, you'd expect to find a three head signal (especially in the case of a CTC system controlled by a central dispatcher) and this is the 'norm' except on lines such as the high-speed multi-track lakeshore line where two head signals are prevalent. The same is true for many ABS (Automatic Block Signalling) systems which have a limited range of indications possible. In the case of modelling using a two-head signal as shown it would indicate a Red-over-Green (421) or Red-over-Blinking Yellow (425) when the switch is set to route into the siding. When the switch is set for main line the signal would act as a block signal (indicating rules 405, 409, 410, or 428).
In the above example we have a single track interlocked with a lift bridge across the Welland Canal at Port Colborne (It has since been removed). Two head signals (not staggered so they can indicate absolute stop) are used to protect trains from continuing when the bridge is lifted. The same signals could be used to protect when two rail lines intersect but this is a rare situation in reality as there are few crossovers on CN or CP's lines. Note that leading up to this interlocking you'd encounter two-head staggered signals to provide advance warning without an absolute stop restriction. A similar situation exists in St. Catharines where the rail line crossing highway 406 runs ovr a bridge over the Welland canal. Approaching the bridge the line encounters a single-head signal, a two-head approach signal (with staggered heads), and a two-head signal controlling access to the bridge.
In this example - perhaps the most straightforward - a signalling system protects a turnout where a mainline diverges into two relatively major lines. The single-head block signal indicates red protecting the train which has just passed. The two-head approach signal indicates yellow-over-green meaning the train is to approach the next signal at medium speed. The three-head signal protecting the turnout indicates red-over-green-over-red showing that the train is to take the diverging route passing through the turnout at medium speed. The diverging route is a major line in this example - had it been a siding one would (i) not take the switch at medium speed and (ii) the siding would likely have a dwarf signal on it.
Where two high-speed mainlines have crossovers these are often protected by signals on overhead bridges as shown. When a crossover is set, one signal in the set of four will not show a stop indication (These are prevelant along the laskshore sub in southern Ontario but are all CTC controlled. In the case of a model I would have these controlled automatically). Since these are high-speed lines only two-head signals are required to indicate appropriate speeds.
Other Signalling Systems
On a recent trip through Western New York State I saw this signal on double-track territory of the Buffalo & Pittsburg Railroad (which was formerly the B & O and prior to that the Buffalo, Rochester & Pittsburg Railway). Thanks to Mark Fischer of the Western New York Railway Society for identifying the road. This line runs parallel to the US219 south of Ellicottville, NY. The signal is a colour-position light signal, not seen on CPR's lines which use colour searchlight signals almost exclusively. I snapped these photos to use as a prototype when I (finally) get around to constructing a layout. Apparent from a later trip, these signals were bring removed from service. Note the 'TCS' plate as well on this signal.
Colour Position Light Signal Indications NORAC Indications