Forms of Color-Light Signals

Forms of Color-Light Signals

Mark's Railroad-Related Stuff
A Pennsylvania Railroad Home Page
Railroad Books of Rules and Signalling: A Home Page
Forms of Color Light Signals

N.B.: Note the licensing agreement before downloading.


This table attempts to show all of the ways (aspects) in which a given indication was displayed. The "most common" representations of a given indication are given in the first column. Generally, these follow AAR aspects and rule numberings. Less typical aspects for the given rule, or aspects that conflict with others, are given in subsequent columns, identified by railroad. These "exception" aspects are meant to be exemplary and fairly complete, but not exhaustive. Signalling pages for the individual railroads are planned to handle the latter need. Note that not all of the aspects in any given column were used by every railroad; and specifically, for the "most common" representations, each RR listed as using these may not have used every form.

All signal diagrams are minimalistic (or telegraphic). The minimum operationally significant elements were shown, with the concession that the signal mast and faces were shown for ease of viewing and understanding. Significance is defined, for the purpose of this page, as that feature of a signal that will cause an engineer to handle a train differently. Those features which are merely informative, without affecting train handling, are considered insignificant. Informative features include staggering of signal heads (nearly always), number or other marker plates (often), etc.

AAR is from ca. 1971.

Related Pages:

Learning the Aspects
Significance of Signal Components

  • Specific notes on the various railroads' usage:
    Rules show number plate only in that case (Stop-and-Proceed) where the number plate distinguishes the signal from another (Stop). Dark arms are explicitly shown in the rules. Insignificant: signal face shape; vertical alignment of faces.
    Rulebook explicitly shows all number-plated versions of signals (not just
    All forms of signals appear to be shown, including staggering and number plate. These two are insignificant, however. E.g, Division timetable showed G/R/R, G/R, G/space/R, all aligned, then G/R/# staggered, G/#, and G. Faces were not shown.
    Modern CSX rules show a single light on a square face (were any square faces really used?)
    Modern CSX rules show 'D' type signal faces, i.e, vertical oblong with round ends and 3 lamps in a vertical row. Placement of colors appears to vary if rules are to be taken at face value. Placement of colors between top arm and lower 2 arms does appear to vary, and this is not unusual practice.
    Besides being the only major US road to use left-handed operation, CNW used type D signals mounted 'sideways'.
    Approach Restricting - is this used in dark or signalled territory?

    I've not yet gotten to the western roads. Comments on these welcome.

    Signalling Styles

    The Basic Aspects.

    Of these aspects, Clear, Approach, and Stop-and-Proceed are generally seen at automatic (block) signals. Some roads used Advance Approach also, some used Approach Medium in identical settings, and some did not use this concept at all. Stop signals are found only at interlockings or other such controlled locations. Restricting is generally used at interlocking (controlled) signals for trains proceeding into unsignalled territory (either entirely unsignalled, or unsignalled for that train's direction of travel). Some exceptions exist (e.g. the eastern grade via Horse Shoe Curve). Stop-and-Proceed may be seen at interlocking signals under special conditions.

    Advance Approach / Advance Clear to Stop
    282A SCL, SOU 301 NORAC, CROR 409
    Note: NORAC removed NYC Y/Y/R as Advance Approach (now Approach Slow).
    Approach / Clear to Stop
    AAR 285, CROR 410 C&O, NORAC C&O
    292, AAR 293, CROR 429 C&O, NORAC C&O CROR 429
    CROR does not use the single-head form in the first column. See also extensive note below.
    Stop-and-Proceed / Restricted Proceed
    291 C&O, NORAC SCL CROR 428
    Note 1:
    This (CROR 428) is the only place where I've found that staggering of the signal heads is significant in the interpretation of the signal's meaning. Note that I'm being quite specific in my use of the word 'significant' to mean 'in and of itself making a difference'. Many roads stagger the heads of automatic signals, and place the heads of interlocking signals in a straight vertical line. And they do this quite intentionally and consistently. However, on these other roads, the staggering does not affect the interpretation of the signal whatsoever. On CROR, it does. (I'm still looking for more examples of significant staggering [pun intended].)
    Note 2:
    AAR shows only red over red, then states in text: "qualified by letter plate, marker light, shape of arm, or combination". Note 3:
    WC (Wisconsin Central) is the only RR I've thus far seen use the term "Restricted Proceed" in reference to what most people would call a "Stop-and-Proceed" signal, as opposed to a "Restricting" signal (see below). Further, this is the only case I know of where the indication for "Restricting" and "Restricted Proceed" was identical.
    Restricting / Restricted Proceed / Restricting signal
    AAR 290, CROR 426 SCL, CUS, RF&P, NORAC SCL, RF&P C&O SOU, RF&P WC 240
    Note: SOU also had R with pointed semaphore blade over #.

    Interlocking Signal Aspects

    (Nearly) all of the speed-signalling aspects are named with a speed first, indicating the speed at which the train must be travelling immediately (through the switches of the interlocking). The second word provides block occupancy information, clear indicating at least 2 free blocks, approach indicating no more than 1 such free block.

    For route-signalling aspects, because of their lack of need to provide speed information, the number of aspects is greatly reduced.

    Cab Speed
    NORAC 281a
    Limited Clear / Limited to Clear
    281C, CROR 411 C&O CROR 411 AAR 281C (ca. 1971)
    Limited Approach / Limited to Stop
    SCL ???, CROR 415 C&O 281D CROR 415
    Note: Many roads' rules lack this rule, as it is viewed to be of questionable safety.
    Medium Clear / Diverging Clear / Medium to Clear
    AAR 283, CROR 416 C&O SOU
    Medium Approach / Diverging Approach / Medium to Stop
    AAR 286 C&O 286 SCL, SOU CROR 420
    Note: R/Y would follow the pattern but generally indicates Restricting.

    Slow Clear / Slow to Clear
    287, CROR 421 CUS C287, CROR 421 CUS

    Slow Approach / Slow to Stop


    288, CROR 425 C&O SCL CUS C288 CUS, CROR
    Note: R/R/Y would follow the pattern but generally indicates Restricting.

    Distant Signal Aspects

    (Pardon the possibly loose usage of the word 'distant'.) Used in advance of the interlocking signals above, to warn the engineer of the speed or route required at the following signal. All are named "Approach" with the speed or route as the last word (cf above). In a sense, all could be named "Full ..." if one wished to create a "fully qualified" name.

    Approach Limited / Clear to Limited
    281B, CROR 406 C&O CROR CROR 406A AAR 281B (ca. 1971)
    Approach Medium / Approach Diverging / Clear to Medium
    AAR 282, CROR 407 C&O CROR 407A WC 235
    Approach Slow / Clear to Slow
    AAR 284 C&O, CUS, CROR 408 C&O CUS, CROR 408 SOU CROR 408A

    Combination aspects.

    These aspects are used at interlocking signals (as evidenced by a speed being the first word), generally in territory with either high traffic levels or with closely spaced interlockings or junctions. Each signal is effectively a combination of an interlocking signal (3 lists above) with a distant signal (2 lists above).

    Limited Approach Limited / Limited to Limited
    CROR 412
    Limited Approach Medium / Limited to Medium
    CROR 413
    Limited Approach Slow / Limited to Slow
    CROR 413
    Medium Approach Limited / Diverging [Route Clear,] Approach Limited
    SOU CROR 417
    Medium Approach Medium / Diverging [Clear] Approach Diverging / Medium to Medium
    283A C&O, SCL NORAC CROR 418 WC 237
    Note: Previous Conrail was R/Y/Gf.
    Medium Approach Slow / Diverging [Route] Approach Slow / Medium to Slow
    AAR 283B, C&O, SCL SOU CROR 419
    Slow Approach Limited / Slow to Limited
    CROR 422
    Slow Approach Medium / Slow to Medium
    CROR 423
    Slow Approach Slow / Slow to Slow
    CROR 424

    Advance Aspects

    One of these aspects, Advance Approach, is also listed with the "Basic Aspects" above. Altough the concept for this aspect (3-block signalling) is a later invention relative to Clear, Approach, and Stop, the concept of an Advance Approach signal is rather a simple one. It is also included here for completeness and comparison.

    Advance Approach
    AAR 282A NORAC AAR (ca. 1971)

    Advance Approach Medium
    AAR 281A

    Medium Advance Approach / Diverging Advance Approach
    283C SCL AAR 283A (ca. 1971) WC 238

    Special-Use Aspects

    These aspects utilized the same signal forms as those above but generally provided "special" information.

    For example, the Caution (etc.) aspect only warns of an upcoming signal (generally an interlocking signal) but specifically diavows providing any block occupancy information. It is most often used when exiting dark territory into signalled territory, when the expense of a block circuit immediately prior to entry into interlocking limits cannot be justified or is not desired. In application by the train engineer (driver), I'm not sure how it's any different from Restricting. In application by the signal engineer, Caution tended to be used upon imminent entry into signalled territory, whereas Restricting tended to be used upon immenent exit from such territory.



    Approach Clear

    Approach Restricting
    WC 234

    Caution /
    Distant Signal

    Take Siding / Stop and Open Switch
    Need R/R/R/black S on white round illuminated, R/R/Splate, R/Splate SCL

    Phase Break

    Switch Open

    Switch Closed

    Slide Protection / Stop and Check
    Need R/R/black C on white round, R/Cplate SCL

    Special Protection Signal
    CROR 427

    Mark D. Bej, M.D.