Advance Caution

Advance Caution is used on the New Zealand railway system to provide a fourth aspect, without the need for a fourth light.

There are other ways of providing the functionality of the fourth aspect and they are also described on this page.


Poor man's Advance Caution at Wallaceville, approaching Upper Hutt.



Advance Caution

The Advance Caution indication is relatively new on the New Zealand system. Here is how it is defined in Semi-permanent Bulletin 342 of 28 May 2002.

Extract from Semi-permanent Bulletin 342 of 28 May 2002

At Ngauranga a new signal indication "Flashing Yellow over Red" has been installed on 2RAB Down Home and 6R Down Directing signals.

The indication will be an "Advance Caution Normal Speed" meaning:-

1. Two sections ahead are clear.
2. The next signal is at Caution Normal Speed.
3. The second signal ahead is at Stop.

Reason - The indication is to warn that the spacing between signals are such that usual stopping distance is not provided
OR
To provide additional warning in adverse weather conditions

ie, next signal displaying "Caution Normal Speed" second signal at "Stop".

Approaching Ngauranga on the Down Main during a southerly storm. Two signals at this station have been equipped with Advance Caution because of these adverse conditions.

( Photograph copyright Bruce Scott).




Insufficient Stopping Distance

The first use of Advance Caution is to warn that the spacing between signals are such that usual stopping distance is not provided. The following is an example from Upper Hutt, although note that Upper Hutt currently (2004) has an Express Freight board.

Braking Problem At many crossing loops there is insufficient braking distance between the Home and Departure or Starting signals. This particularly applies to freight trains. There are several solutions:

Express Freight Speed Board imposes a speed restriction approaching the station.

Advance Caution A flashing top yellow indicates that the next signal is at caution.

Double Caution Two signals in rear of the Stop signal display yellow. Note that in Single Line Automatic (SLA) areas caution on the intermediate and also on the Home indicates that a train is approaching in the next block.

Example The example on the right is from Upper Hutt. Currently there is an Express Freight 70 board near Wallaceville station. If intermediate signal 3116 were fitted with either Advance Caution or Double Caution the speed board could be removed and freight trains would be able to maintain line speed through the area.




Adverse Weather

The second use of Advance Caution is to provide additional warning in adverse weather conditions. Here is an example from Ngauranga. See also a Driver's View of Ngauranga   (in a southerly storm).

Salt Water On Track The Down Main at Ngauranga is next to Wellington Harbour. During a southerly storm sea spray and waves land on the track, making accurate stopping and starting difficult.

Advance Caution has been installed on two signals at Ngauranga to increase the stopping distance. In the example shown (right), if 10R is at Stop the the installation of Advance Caution on 2R has increased the stopping distance from from 601m to 1074m.

Similarly, If automatic signal 411 is at stop the use of Advance Caution has increased the stopping distance 411m to 1012m



Last Updated: Sun May 19 2013.

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