Ngaio Signalling

Changes in signalling at Ngaio, from the mechanical signalling of 1924 to the automatic signalling of the present day.

I have taken four snapshots so some of the changes may have occurred at an earlier date than that listed.

Right  4LB Down Departure From Up Main at Ngaio. Note the grade.


1 Up distant 18' 0"
2 Up Home Main Line 22' 6"
4 Up Home Loop Line 16' 6"
20 Down Starter Loop 24' 6"
22 Down Starter Main Line 27' 0"

11 Shunt Loop or Siding to "S" B'Shunt or Main 17' 0"
7 Shunt Mainline 17' 0"
14 Shunt Loop or S'dg to "N" B'shunt or Main 17' 0"
18 Shunt Main Line 17' 0"

5 Up Starter Loop Line 24' 6"
3 Up Starter Main Line 27' 0"
23 Down Home Main Line 27' 9"
21 Down Home Loop Line 21' 9"
24 Down Distant 18' 0"

Repeater shunts   Note that 11 and 14 shunt signals are repeated.


Motor points and colour light signals were probably installed at Ngaio in early 1938. I do not have a copy of the relevant S & I to confirm this. Tablet remained in operation until the third of July 1938 when it was cancelled. The full Wellington - Johnsonville automatic signalling came into operation on the fourth of July 1938.

Points other than loop points are rod-worked from the lever frame.

A-lights on the Up & Down home signals avoid detention of a train at the respective home signals in the event of a preceeding train failing or a track fault occuring within station limits.


Goods siding and mechanical shunt signals removed. Signal box replaced with station control panel on western side of track.

Up Departure from Down Main and Down Departure from Up Main signals installed. Colour light points indicator and Arrow Indicator installed.

Up Starter converted to single unit and re-classified as a Departure, thus removing the facility to divide up trains. 25 Shunt From Main signal removed.

"Distants" renumbered from "R3" to distance based format. Did their function change? Points and signals re-numbered.


CTC was installed and signals re-numbered using the conventions for remotely controlled loops. Ngaio becomes an unattended crossing station. The A-Lights were removed.

To avoid expensive changes to the interlocking the low-speed lights were set up to prove the track unoccupied, which is contrary to normal practice.

In 1977 distances had been metricated.

Last Updated: Sunday, July 24, 2005

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