Color Usage in Signals, Signs and Markings - Signal Colors: Combinations

Color Usage in Signals, Signs and Markings - Signal Colors: Combinations

Combinations of colors and their meanings in railways is problematical. It is difficult to write succinctly about the meaning of signal colors for the various systems, and combinations are much more of a problem. A comprehensive coverage of the subject would require examination of individual codes; hopefully a brief treatment will provide some notion of combination signals. Appendix II provides details on signals for larger systems.

While there is a broad range of color combinations only a few forms are recurring: GY, YR and GR being the most important. Less frequent combinations include GW, RW, and YW; white provides a common denominator. The complexity of combinations is increased by a dual character: GR can also be RG, and GY can be YG. The order of signal colors can increase or decrease the restrictive (or non-restrictive) degree of signal indications, as in the U.S. and in Canada.

A general "rule" about color combinations might take this form: the upper color of such a combination is the dominant or at least more important of the colors that are present. The lower color, though secondary, is a modifying agent of the upper hue. For example, a YR (yellow over red) combination is cautionary with a tendency toward some restriction. A RY (red over yellow) tends towards restriction though somewhat reduced because of the cautionary modifier; R over G would decrease the proceed character of the indication, Y over G increases the cautionary status of a proceed indication.

GY (and YG) represent the most common color combinations with nearly one-half of the systems containing a form of G and Y. The restrictive character of GY/YG is less than Y or YR. It is the only combination common in Europe: both URO and Western European systems frequently employ GY. It is present in African, Asian and American systems (including those of Canada and the U.S.). A typical GY pattern is that of Austria where it signifies a maximum speed of 40km/h (single G indicates simply "Frei" or proceed; two greens permit 60km/h) (OBB 1979, 15). There are many forms of GY in URO including GY (40km/h), GFF/Y (40km/h to 120km/h) and GFF/Y and one Y strip (60km/h to 120km/h) (URO 1962).

GR (and RG) are employed by less than one in four systems. Only a small number of European systems display this aspect. A variety of English-speaking nations use these aspects (KR, PR, NSW among others). It also is found with several larger Western Hemisphere nations. GR indicates clear in a complex system, with multiple signals, while RG denotes a clear signal with a degree of restriction. Brazil, for example, employs both G and GR for maximum speed while RG indicates limited speed (RFFSA).

YR (and RY) are found with a similar range of nations, and more European systems than was the case with GR. Australian National Railways (employing the former South Australian code) mirrors a common usage for YR/RY aspects: YR calls for a cautionary response by the train crew and at normal speed; RY is a cautionary message at medium speed; and the more restrictive RRY requires the train crew to proceed at low speed (shunting) (ANR 1947, 109-110, 112) . RY indicates proceed at slow speed at selected divergent routes for Taiwan (TRA 1989). A more singular variant is the Y/FLR indication of Denmark that denotes stop and then go slowly (DSB 1985, 34-3).

Canada and U.S. signals are complex because of many aspects and indications. Some of these indications are also found in Asia, Australia, and other parts of the Americas. Appendix II provides a review of these signals. In brief, clear has four levels: basic clear, limited-, medium- and slow-clear. In nearly all instances, G preceeds R for basic level, and R preceeds G for qualified forms. Three-aspect signals add an additional G or R (BOTC 1961, AAR 1965 TISRPS). The second category includes approach-limited, -medium, and -slow signals. These are marked by YG or GY indications; three-aspect approach signals include R. Limited-, medium-, and slow-approach signals manifest some form of YR or RY; restricting signals also follow this pattern.

Two U.S. advance-approach signals also are YR/RY.

Some systems combine a regular signal color with a special color (blue, purple, white, luna white). Many examples are found in Europe; for example Portugal employs blue and red for one form of permissive stop, and Poland uses white and red for shunting (CP 1981, 19; PKP 1975, 197-198). Frequently these combinations are fo specialized purposes. For example, UK and Australian systems frequently combine white and red in shunting signals (UK K&W 1963; see also various Australian signal codes). Zimbabwe combines white and yellow as well as red for shunting work (ZNR Thompson 1987). The use of white reduces the possibility of confusing a shunting signal with a mainline one. There are other instances when a special color and a regular color have mainline significance; for example, Portugal employs lunar white and red t indicate a permissive stop as well as for shunt signals (CP 1981, 19). At times blue is combined with red for various authorized movements including shunting (RENFE 1-10). White is found with red in Belgium for various authorized movements (SNCB 1967, 37). China employs lunar white with blue for shunting, and red and lunar white for call-on signal indication (Xian 1989) .

The use of special colors for non-mainline roles (and the use of special colors as qualifiers of mainline signal indications) are sometimes joined by full participation of special colors in mainline signals in some systems. This is very much in evidence in the Netherlands where white constitutes a fourth regular color (contrary to other systems) for color-light signals. White is utilized as much as green, and is found in combination with both yellow and green. Examples of such messages include WWY indicating the next signal will be red, and GWW indicating maximum speed on main line. GWG indicates next signal at WWG and divergent line open at 45 km/h. (NS 1978, 22, 23; also ETR 1952).