Color-light Signals: Forms & Configurations

Color-light Signals: Forms & Configurations

Color-light signals are the most common type of railway signal in use today. They are probably one of the very few visual signals that is experiencing any growth in numbers. This signal can be a simple signal consisting of the signal head, baffle and supporting mast or bridge; the head contains the lamp units, lenses, and electronic or electro-magnetic mechanism. The signal in its basic form exhibits green, red, and yellow lamps, with a resulting three messages. But the color light signal and messages are simple only in the abstract, and in the most basic form. Over many years, and through the mediation of many rail systems, the color light signal has evolved and expanded into many variant forms and configurations. The variant classification in Chapter 29B1, and the illustrations of representative signal shapes, Chapter 29C, will augment this segment of the study.

References to the beginnings of color-light signals favor the U.S. very much. This is due less to national chauvinism than to the fact that many of the lighted signal developments took place in the U.S. Short—range all—lighted color signals date back to the very early years of this century; long-range types were established in 1914. Search-light signals began in 1915. Color-position signals began the year following the search-light signal (AAR 1953, 69-70) .

The search-light is a precisely aimed signal; in fact, sights are included on the signal head for that purpose. Signals are designed for left and right-hand curves as well. The signal is a more expensive unit than the standard color-light signal (Armstrong 1957, 12). The multi-lamp type may be preferred to the search-light signal in some territories because of problems in using the former type of signal where special problems occur including that of track curvature (Armstrong, 1957, 12) ; it can be noted that some rail specialists are not in agreement with Armstrong on problems of the searchlight signal on curves. The precision of the search-light signal can be illustrated by the former usage of it by the U.S. Coast Guard in marine ranges (General Railway Signal, 1960).

The color-light signal can be divided into two basic forms: the multi-lamp/multi-lens form, and the single lamp/multi-lense forms. The second form is frequently termed the "Searchlight" type though it is also known as the "single-lens" in South Africa (SAR refers to the multiple-lamp as "Multi-lens"; SAR 1964, 13). The color-light has from two to five aspects or positions, though more than five are possible in some configurations. Two signal heads become necessary especially in systems where installations requiring more than three aspects are permitted. This is also true of the searchlight signal since it is incapable of more than three aspects per unit. The searchlight has one configurations and no variants. But the multi-lamp type explodes into a verdant jungle of configurations which forms must be reviewed.

Configurations in this study do not refer to the number of lamps to be found with a given signal. Instead they refer to the arrangement of lens and lamps within a signal unit. Readers familiar with railway signals of a simple form may initially find this puzzling since they may be accustomed to a signal housing consisting of a single-row pattern of perhaps three lamps; and assume that there are no other patterns. Simplicity is not always a hallmark of all railway systems (URO and North America are prime examples of complex systems).

Configurations can be divided into three principal categories: basic, modified-basic, and complex. The complex can be further divided into a standard-shaped signal head with irregular lamp arrangements, non-standard-shaped-head with irregular lamp arrangement, or a signal-head deploying multi-symbol patterns either within a standard configuration or a non-standard configuration. "Standard" in this study - and this may be somewhat arbitrary -refers to basic geometric shapes which are favored in most systems; patterns that are symmetrical and balanced. Special shapes are those shapes at variance with common design forms. Standard arrangement of lamps refers to an arrangement in which the lamp follows the contour of the signal head, and most often this is a straight-line, vertical-orientated pattern. Patterns that are, for example, "scattered" over the face of the signal are not standard.

The basic configuration is a vertical unit with two or more lamps. The most common version has three lamps though one or two additional lamps are not uncommon. The basic model has one row of lamps which are spaced equally apart.

The modified-basic configuration has undergone some change from the basic form but not a change that is a drastic re-ordering of design. The basic modified models include a horizontal version of the basic vertical form, and a triangular form. A somewhat more altered version contains two rows of lamps but within the basic form.

Complex configurations include more substantial changes. These can be sub-divided into three major categories. Type I contains those signals with a standard shaped-head but with an irregular lamp arrangement. Lamps may be located in some areas of the signal head surface but not in other areas depending on specific needs. Lamps may in fact be "scattered" about the surface depending on the needs of the signal operation. Despite the arrangement of lamps the shape of the signal head is a simple-geometric form.

Type II configuration consists of those signals comprizing both non-standard heads and lamp patterns. There are several forms within Type II. These include the triangular-rectangular form which consists of five lamps in the rectangular portion, and a single lamp in the triangular portion; see Chapter 29C for an illustration. A second form is the "V" pattern consisting of two rectangles positioned diagonally and joined at the base.

Type III configurations include those complex situations in which more than one kind of symbol is employed. This does not refer to marker lamps, and other adjunct lamps which are part of a given signal installation but separate from the principal head though frequently attached to the same signal mast. The diverse symbols possible with Type III include the standard circular lamp, alphanumeric signal, groupings of small lamps that operate as a unit, and other symbols which can be loosely summed up as graphic symbols. All of these diverse offerings, for example, can be found in the URO system. Type III configurations are single signal heads rather than multiple heads. Type III may need to be further divided into Ilia and Illb: the former containing standard signal heads; the latter non-standard.

The previously described configurations, whether basic or complex, refer to the essential form and not to nuanced differences. The true square, rectangle, or triangle is almost a rarity in railway signalling. Frequently one, or both ends of a rectangle have rounded ends, or at least rounded corners; squares may not have rounded sides but may have rounded corners. Other signals have the corners of the signal head or baffle "cropped" off. In yet other instances one side or end will be altered but not both. Chapter 2 9C provides illustrations of these various features. The configurations classified in this study do not consider the size of the signals as a basic concern. But there are differences in signals and this is only partly due to the number of signal lamps. And the size of the lamps is not a factor unless there is a very noticeable difference in lamp size. For example, signals that contain lamps that are only 12 inches in diameter (30cm) are noted but those from five to eight inches or more in diameter are not separately noted as significant for the study.