Color Usage in Signals, Signs and Markings - Basic Colors

Color Usage in Signals, Signs and Markings - Basic Colors

Green can be regarded as an ubiquitous signal color though of more recent vintage than red. White, rather than green, served as a proceed color for much of the nineteenth century and for some rail systems into the twentieth century (AAR 1953, 73) . The French firm of Chappe Brothers established green as a caution signal in 1841; English railways selected green as the official proceed color in 1893 (AAR 1953, 73; UK K&W 1963, 10). U.S. railways did not follow suit until 1906 (AAR 1953, 73). Despite divergent meanings in the nineteenth century, green now has a clear and universal meaning for railways and traffic control devices (marine and aeronautical aids to navigation utilize green in a different mode).

Secondary colors have a limited or specialized range of uses. This is not the case with green which can be found with mainline signals, on sidings, in train yards, controlling shunting and other functions (secondary color usage reduces the frequency of green for specialized functions but does not eliminate it). For many systems, including those of the Americas and UK-influenced systems, green is frequently a fixed and single-lamp signal. But in Europe much more diversity is found: doubles, triples, flashing green (both slower and faster versions) signals are relatively common. While no one system has all varieties, the full company of forms will be found within Europe. Double greens are found in systems from Canada to Pakistan (BOTC 1961; PR T-A S). Multiple greens are found in more complex configurations rather than basic message forms. Fixed multiple greens are not confined to the URO system; for example, Sweden is a heavy user of those forms of green (URO 19 62; SJ 1979, 19, 22). Some use of flashing signals is found in the Americas; for example, they are in use in the Conrail system (McKnight 1990) .

The color green in essence means proceed. The various nuances and qualifications indicate differences in degree of maximum speeds; the essential message remains constant.

Red has a longer history in its essential message of halt/danger than the messages associated with any other color. Volume I, Part A of this series provides information on the background of red. Early railway usage of red closely follows present day usage. It is a general purpose color fulfilling many functions (red, like green, is sometimes reduced - if not eliminated - for specialized roles). Red is less often affected by variant indications than green or yellow. Halt is most often signified by a signal and fixed red lamp. France and Canada use a double red for an absolute stop with single red for permissive stop or other variation. Flashing red can convey several meanings including that of deferred stop (BOTC 1961, 115; SNCF 1981. Some Australian systems also employ a form of double red for stop indications (McLean 1990) . Brazil has "stop and proceed at restricted speed prepared to stop" (RFFSA 1965).

Yellow with its ascribed meaning of caution is a more recent signal indication than green with its assigned meaning of proceed. Earliest uses of yellow for caution appear to be in the U.S. (AAR 1953, 73), and the Orange River Colony (South Africa) (Institution 1944) .

The Word "caution" encapsulates the meaning of yellow though frequently some other word is employed to convey that meaning. France speaks of "avertissement" (warning) (SNCF 1981); Spain of "annuncio de parada" (annoucement of stop) and Portugal, "precaucao" (precaution) (RENFE 1978, 1-9; CP 1981, 19) . Brazil, a second Portugese-language system employs "limitado" (limited) (RFFSA 1965), and an American Spanish-language system, Argentina, has "precaucion" (precaution) which is employed by other systems in the same language (EFFA 1958, 110). German-language usage includes "Langsamfahrt" (slow) (DB 1981, 19). U.K. simply calls it a caution signal, and South Africa offers the variant, "proceed with caution" (UK K&W 1963, 52; SAR 1964, 16). The U.S. and Canada operate a variety of cautionary signals and all contain the word "approach" (BOTC 1961; AAR 1965). In URO yellow indicates a speed limit that requires a reduction of velocity (URO 1962). IUR describes yellow as indicating "a warning to stop" (at the next halt signal presumably) (IUR 1951-2). Frequently the caution message indicates "proceed but be prepared to stop at the next signal" though variant wording may be employed. Flashing yellow uses include proceed-limited in Brazil (RFFSA 1960), and "decelerated advance in hump signals for China (CR 1989) . Despite uncertainty about terminology the meaning of yellow - in operational usage - is relatively uniform though less so than that of red or green.

The common form of yellow signal is that of single and steady (one lamp unit in a fixed pattern). Double yellow for a preliminary caution is recommended by IUR and presumably this has influenced the increased usage of it (IUR 1961) . Double yellow can have variant meanings include upcoming divergent route (Taiwan; TRA 1989)), and divergent route (Bangladesh; BR 1989); China has a similar use of yellow (CR 1989) . European systems, UK-influenced systems and a variety of Third World nations have double yellows for preliminary caution. Some flashing yellows are in use; URO is a notable user of such signals (URO 1962; see Appendix II). DB employs a triple yellow but only in a very specialized role (DB 1981, 32a) . Dpuble yellow in India indicates "proceed, pasj the next signal at restricted speed." (IR, 7) .