Taita and Petone Compared

The Taita and Petone interlockings are of the same vintage and use the same technology. However, there is a significant difference in the behaviour of the two interlockings. This page explains why the Signalman must operate the Taita panel more precisely than that at Petone.

Another difference involves blacked out signals. At Petone a blacked out signal shows a stop indication on the panel. At Taita, if the signal has been cleared, a proceed indication shows on the panel.

Petone and Taita Compared

Observed Difference Between Petone and Taita

At Petone the signalman, provided he does things correctly, never has to wait while timers run down. Of course, if he wrong routes a train and takes the light back a timer will start but that is not operating the panel correctly.

At Taita signals can become approach locked, requiring a timer to run down, even if the signalman operates the panel correctly. The problem happens when a second train is closely following another and can be anticipated. Sometimes operating the switches in a particular squence will prevent the signal locking. At other times all the signalman can do is watch and hope that the two trains do not occupy a particular combination of tracks circuits.

Reason for Difference

At Petone when a train passes a signal the approach locking is released and the back locking applied. This means that a closely following second train does not approach lock the signal.

At Taita the approach locking is not released when a train passes a signal. This means that a closely following train can approach lock the signal if it occupies the approach circuit when either the first train is on the backlock circuit or the switch is still in the reverse postion.

Operating Taita

To avoid approach locking signal 1 the switch for signal 2 must not be reversed until Train A is clear of A track AND the signal 1 switch has been placed Normal.

In practice, when a second train is closely following a first, the signalman must put each switch back to Normal promptly as soon as the train has passed the signal and only then clear the signal in rear.

Note that there is no Outer Home signal on the Up Main so the second part of the technique does not apply to the Up Home. The signalman must keep his fingers crossed that a closely following second train does not approach lock the Up Home.

Approach lock release

Last Updated: Saturday 1st February 2014

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