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Meanings of Colors in Railway Signalling
 
Meanings of Colors in Railway Signalling


There are seven principal railway signal colors. This number was determined with the aid of NBS incorporating the work of CIE (Breckenridge 1964, 1967), the practices of numerous railways, and the publications of railways and other groups. Signal colors include the universally recognized ones of green, yellow, and red. They also include the less frequently utilized ones of white, and lunar white, and the infrequently used colors of purple and blue. The "colors" of orange, amber and violet are not actual color hues; this matter is discussed in Chapter 30B3.

Colors and meanings are examined from three perspectives for this study: a) whether or not the meaning ascribed to a color is intrinsic to that color; b) the use of colors in various railways; and c) color usage in partially light and unlighted signals, signs and > markings. Some overlap may occur in this tri-part approach.

Each of the colors is visually different from all other colors. However, color meanings are not distinguished solely by the meanings ascribed to the color hues; other factors can determine meanings. It is possible to speak of two levels for types of meanings in signal color usage. Type I refers to color hues that have intrinsic meaning while Type II includes those colors generally receiving meaning from external factors.

Green, yellow, and red are among those hues with specific meanings intrinsic to them, and which are employed on a universal basis. Green, whether in railway usage or in other transportation modes, indicates proceed (or go or line clear); red indicates stop or halt; yellow supplies a meaning of caution. Various terms, such as proceed and halt, can be replaced by other terms but the significance of the message remains constant. Yellow has a more complex meaning structure within railway usage.

A report of the "Three-Position Signal Committee" to the IRSE in 1924 provides a workable summary - despite the intervention of 65 years - of the various meanings of caution:

a) "proceed cautiously."

b) "next signal is at 'danger'."

c) "be prepared to stop at next signal."

d) '"line clear' for braking distance ahead." (Nock 1962, 1971).

The committee favored (c) though all of these meanings of caution, and other nuanced versions, are in use; a complex system such as that of AAR provides variant forms of most of them. Ultimately yellow - no matter how the message significance is formulated - means a readily understood message of caution or of restriction. It is true that meanings attached to green offer some variant meanings but the range of possible meanings is narrow and green presents a substantially straightforward message.

The uses of blue and purple represent a complex matter. Those colors may have intrinsic meanings but only in a few systems and those few systems may not be in agreement. A possible degree of intrinsic meaning and one that is sometimes shared may exist but the evidence is too scanty to say more than that. Purple has been used as a substitute for green in situations where green on a secondary line is near a mainline signal displaying green; which is a role also performed by white.

In meaning structure Type II, the meaning of the color is not found in the color itself but is imparted to the color by an outside factor; this does not preclude color from having both intrinsic and extrinsic meaning formulations. In many instances a signal manifesting a Type II function is some form of position-light signal; some color-position signals may also be represented.

In some instances (Type Ila) the color serves as a substitutes for semaphore arms; for example, in the U.S. position-light signals display amber (yellow) indications but in this instance the yellow does not represent a caution message but rather the "arms" of a semaphore signal (General Railway Signal 1925; also Kopp 1987) .

In a second form (Type lib) the color -often times white or lunar white - serves to illuminate graphic or geometric-shaped symbols at points/switches or at route/junction indicators. At many of these signals black serves as a boundary or background color for the white symbols.

In a third situation white or lunar white is combined with a standard color. These indications are frequently for shunting signals. This creates a color-position signal and may suggest a Type I signal since the white acts as a substitute for green (and eliminates confusion with a mainline signal) and the standard color indicates halt. But the signal is also a position type of indication and thereby suggests semaphore arms as well as intrinsic messages. Type lie can be viewed as a composite signal.

The following six segments of Chapter 30A may appear uneven. This unevenness is caused by the nature of signalling systems and their degree of complexity. Those signals that are simple are explained here in their entirety. But only the salient features of more complex systems are reviewed here; details of those systems are included in Appendix II (a more detailed summary of all "A" and "B" class systems are included in that Appendix).

СЦБот 21.11.2023 09:21

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