The Union of African Railways Signal System

The Union of African Railways Signal System

The Union of African Railways (UAR) has substantially completed a signal system for its member states (UAR 1981, TIRSPS). The system is operational and constitutes a code rather than general guidelines. This code is on two-levels: traditional practices - based on French and UK practices - and an all-lighted signal system. The UAR code incorporates existing practices, and thereby makes official and orderly notions of a more limited provence available to a larger realm.

The mechanical signals of UAR may seem out of place in a new code but as long as such signals are in use they from a part of any signal code. The UAR semaphores and signal boards include African systems with a French heritage or British heritage. The coverage of these signals provides a comparative summary of two major approaches to signalling that transcend the specifically African milieu.

A UAR working group was established in 1980 to prepare the signal code and "preliminary UAR draft document" and was completed in the following year. By 1983 a final draft document based on the first draft was completed. This draft was adopted by the UAR Signalling and Telecommunications Committee and was to be submitted to the membership of the Union. This compiler received a copy of that 1983 draft in 1987 but it contained no mention of approval by the member-states. The purpose of the code is to harmonize present signal systems "in anticipation of the interconnection of the railways." The code was also intended to improve safety, increase freight capacity and save on labor costs.

The system includes fixed signals, grade (level) crossings, hand signals, acoustical signals, and temporary warning boards. The study does not consider grade and hand signals. Fixed signals include mechanical, and color-light signals, and also permanent warning boards. The last category includes speed restrictions, whistle and some miscellaneous signs.

The French railways in Europe have historically placed importance on signals at stations and limited significance for signals away from stations (Allen 1982, 146-147) . English signals - though signals are found at stations - are often found in larger numbers away from stations. However, an emphasis on signals at stations is found in UAR for both English and French approaches. It may be noted that early signalling in English-speaking areas of East Africa also placed importance on signals at stations (Hammond 1964, 74). It should be noted that older signals are often near stations because of the manual nature of earlier signals (McLean 1990) .

There are two main mechanical forms for UAR: the station protection signal (comparable to a home signal), and the warning signal.

The French form for station protection consists of two-sided signal boards with a red/white check pattern on a square board (perpendicular to the track) for the warning indication, and a solid green pattern (parallel to the tracks) for the proceed at reduced speeds indication. In Europe proceed indications in signal boards manifest a blind edge but UAR provides a positive proceed marking (though RAN follows the the French practice of a blind edge). The English style signal is an upper quadrant semaphore (red arm with white stripe and three roundels). The horizontal position indicates stop, the 45 degree position, caution, and the vertical denotes proceed.

The warning signal for the French signal is a yellow diamond in a fixed position and located 1000m from the station protection signal. The English signal is a semaphore with yellow arm, dovetail-end and black stripe. It too is 1000m from the station. This signal has two roundels indicating either a message of caution or proceed.

Color-light signals for UAR are unified. The messages are the commonly accepted ones of green for line clear, yellow for caution and red for stop. A flashing red light indicates that a train is on a siding and should stop at the station according to standard procedures. A white light, fixed or flashing, indicates caution. Any flashing light, yellow or green, denotes a less restrictive pattern.

Most audible signals are human-generated or issue from trains and are outside this study. Detonators that indicate trains are to run at caution for 1500m, and are track-mounted constitutes a transportation marking. Railway signs for UAR are primarily yellow in background with black lettering or graphic symbols. Signs referring to stopping are black with white symbols.