THE SIGNAL BOX

SIGNALS

SEMAPHORE SIGNALS

8. Improving the view

Conditions are not always perfect, so it isn't always practical to install text-book signals. Curves in the line, bridges, buildings and station awnings can all have an effect on how good the view of a signal is to a driver.

A number of adaptions to standard signalling can be applied to achieve improved sighting. The simplest means (and the most common) is to simply make the signal taller or shorter, whilst another is to reposition the signal on the opposite side of the line.

Colour light signals do not present the same issues as semaphore signals as the signals themselves are far more compact and are thus easier to place in an appropriate position. In most cases, a standard colour light signal can be used as a replacement for the special types of signal described here.

Bracket signals

Bracket signal (lower quadrant) Bracket signal (upper quadrant)

Sometimes, the view of a signal can be improved by bracketing it out from the signal post.

This method is often used where the line is curved, and also where there isn't room to position the signal alongside the line to which it applies.


Bracketed two-aspect colour light signal
Lower quadrant Upper quadrant Colour Light

Co-acting signals

Co-acting signal (lower quadrant) Co-acting signal (upper quadrant)

Another method of improving the view of signals is to provide duplicate, or co-acting, arms on a tall post.

This method is often employed near bridges, and also at stations where the awning obstructs the view. The upper arm(s) will be visible from a distance, but only the lower arm can be seen when close.

Co-acting colour light signals are rare.


Co-acting colour light signal
Lower quadrant Upper quadrant Colour Light

Restricted space signals

Centre-pivot signals Shortened arms

Where clearance is limited, special arms may be provided.

The left-hand example has the signal arms modified so that the the arms pivot near their centre - these are known as centre-pivot signals.

The right-hand example has shortened arms. As this makes the signal less easily viewed, this type of signal was always provided with powerful electric lamps, known as intensified lighting. Such lighting could also be found in conventional signals where visibility at night was poor, perhaps against a background of street lights. Any signal with intensified lighting that had both stop and distant arms was arranged so that the lights in the distant signals were not illuminated unless the stop arm was off.

There is no direct equivalent of these signals in colour light form.


Three-aspect colour light signal
Lower quadrant Upper quadrant Colour Light

Repeater signals

Repeater signal (lower quadrant) Repeater signal (upper quadrant)

Another way to give a driver sufficient information about the signals ahead is to use a Repeater signal, which will be positioned approximately 200 yards before the signal.

The signals consist of a black bar (with fish-tail end in the case of a repeater for a distant signal) on a white translucent disc, lit from behind. It is electrically operated, working directly with the signal to which it applies.

This type of signal is often referred to as a Banner signal, but this term refers to the type of signal rather than its function. It can be correctly described as a Banner Repeater signal.

The modern equivalent is achieved using light generated through fibre-optic cable - giving the same indications without moving parts.

Fibre-optic repeaters for distant signals are feasible, but none are known.


Fibre-optic banner repeater signal
Repeater signal (lower quadrant) Repeater signal (upper quadrant)  
Lower quadrant Upper quadrant Colour Light