The New Zealand Railways Magazine, Volume 1, Issue 8 (January 15, 1927)
Automatic Signalling — Keep the Trains Moving—(concluded)
Now there are times when you will pass the nearest automatic signal to a crossing loop (which signal applies in the direction of the loop) and this signal may be at caution (yellow). This will indicate that a train is opposing you in the next section ahead, as has been referred to in a previous paragraph. It should be understood that these hints are only given for the information of anyone who wishes to know if there is train traffic about, and are separate from and in addition to, the usual indications found when following a train within its controlling distance. This information obviously applies to single line working.
The pending installations are double line Westfield-Papatoctoe. Single line Papatoctoe to Mercer and Mercer to Frankton Junction; electric power interlockings at Stillwater, Pacroa, Pacrata, Papakura, Papatoetoe, Whagnarei and White's Line, the latter station being part of the new Hutt Valley double line which is also to be equipped. Proposed installations are Auckland yard, Panmure, Orakel, Sylvia Park, Glen Innis and the double line Auckland-Westfield deviation.
The larges installation to date will be the new Middleton marshalling yard with 65 lovers and 52 points motors. This will be one of the most up-to-date yards from all points of view, in Australasia, and will fill a much needed want and afford goods traffic marshalling for increasing traffic for a good many years to come.page 37
With the exception of the Lambton-Upper Hutt system, all other installations are of the daylight colour light signal system, the indications being given by specially designed and arranged lamps and lenses. These are very powerful and can be seen in bright sunlight for distances of 800 yards and are often visible at a mile, whilst at night the different indications can be seen for miles when the atmosphere is clear. One of the greatest advantages of the colour light system is that in foggy weather the indications are visible at quite a distance from the signal location, the moisture particles in the fog acting as reflecting prisms thus giving a great spread of the coloured beam of light.
For opposing movements on single line working, each departure signal at the crossing loop ends is a positive signal and cannot clear unless the opposing departure signal at the crossing loop in advance is at “danger,” and once at the “clear” position cuts off all feed for all opposing signals.
In conclusion I would like to mention that practically all railways of any importance are equipping, or considering the installation of this system of signalling. In the United States everything has been standardised by the Railway Signal Association, the conferences of which are held quarterly and attended by signal engineers or their representatives from all parts of the country.