Johnsonville Line Signalling

The steeply-graded single-track Johnsonville Line was unique in New Zealand signalling - the points and signals were operated automatically by the trains operating under Single Line Automatic Signalling. Today the line is operated by CTC although a small remnant of Single Line Automatic remains.

This page describes the operation of the branch, with some history to put it all in perspective.

(Right) In this 2005 view a freight train departs for Palmerston North via the Tawa Deviation as an English Electric EMU climbs the grade to Johnsonville on the old route to Tawa.

Two routes out of Wellington


A Very Brief History
The Thorndon - Johnsonville - Tawa - Palmerston North line was opened in 1885 by the Wellington & Manawatu Railway Company (WMRC). In 1908 the line was purchased by the government. In 1937 the Tawa deviation was opened and Thorndon - Tawa was closed. In 1938 Wellington - Johnsonville re-opened as an electrified railway with automatic signalling.

When owned by the WMRC the line was operated under Open Section and Line Clear. In 1908 Tablet was installed, the sections being Thorndon - Ngaio and Ngaio - Johnsonville. From 1938 the line was worked under Single Line Automatic (SLA), with left hand running at crossing stations and automatic operation of points and signals. Uphill trains had priority. In May 1998 Centralised Traffic Control (CTC) was installed. The Controller can switch to automatic mode in which case non-vital software manages the crossings.

Over the 2008/09 holiday period the branch was closed to allow track in the tunnels to be lowered. Wadestown, Ngaio and Khandallah were extended to allow 6 car trains and a substation installed at Ngaio. Searchlight units were replaced with LEDs and several banner indicators were installed.

Johnsonville Line Schematic

The Branch In 2014

The diagrams on this and other pages are my interpretation of past and current signalling arrangements. They are not official diagrams.

Johnsonville 2014 Signalling

Daily Operation

The Wellington - Johnsonville Railway is single track, with crossing stations at Wadestown, Ngaio and Khandallah. There are no passenger facilities at Wadestown. Operation of points and signals is usually automatic, although Train Control can operate them if required. Under automatic operation running is left hand.

The line can accomodate a maximum of four trains at a 13 minute headway. For many years four trains ran during the peaks. However, with a crossing at every crossing-point for every train, if one train had a problem everything came to a standstill, with no slack anywhere to help recovery of timekeeping. Therefore, some years ago one peak train in four was deleted - for example there are departures from Wellington at 0654, 0707, 0720, deleted, 0746, 0759, 0812, deleted.

Interesting features

A remnant of the original Single Line Automatic Signalling remains. A yellow on an intermediate may indicate that the next section is occupied by an opposing train, advising the driver that there will be a crossing.

Safety sidings are installed at crossing places so simultaneous berthing is permitted.

An unusual feature is the use of Low-Speed lights to prove that the track is unoccupied, which is contrary to standard practice.

At Wadestown a train-stop trips down trains if the speed exceeds 25kph.


Click on a link for detailed information....

Operating the branch in 1953

This precis of an article in the August 1953 edition of the Railway Staff Bulletin describes the operation of the Johnsonville Line in detail.

Signalling History

Johnsonville in 1917, 1938, 1960, June 1969, July 1969 and 1998.

Ngaio in 1924, 1938, 1969 and 1998.

Thorndon in 1928.

Khandallah in 1938, 1969 & 1998.

Wadestown in 1938, 1969 & 1998.

Raroa Stockyard Siding.

Mechanical Train Stops

Train Stops   at Ngaio, Khandallah and Wadestown are operated mechanically by a rod from the points motor. Other train-stops in the Wellington suburban area are electrically operated.

In 2008/09 the train stops were removed when Wadestown, Ngaio and Khandallah were extened to allow 6-car trains. I do not know if the replacement train stops are electrical or mechanical.

Photograph Gallery

A selection of photographs taken on the Johnsonville Line.

Tablet Working Tawa - Kaiwarra

Although it is not not part of the Johnsonville Branch I have included this interesting diagram showing signalling arrangements between Tawa and Kaiwarra in 1936. The diagram shows one of the temporary arrangements as the deviation was brought into use. The junction of the "Branch Line" at Tawa is also shown.

Special Locks And Keys

In 1913 the loop facing points and semaphore signals at Johnsonville were interlocked with special locks and keys. It is possible that these were Woods locks, although I do not have any evidence. The proposed installation was described in Train Advice 1913/12.

Eight-car Train

After a train failure an eight-car EMU ran on the Johnsonville Line. This caused an interesting signalling situation at Khandallah, where the unusually long train crossed a two-car set.

Signalling & Interlocking Circulars

A list of relevant Signalling & Interlocking circulars.



Local Instructions
Ngaio L26   July 1969. (206k)
Johnsonville L29   July 1969. (205k)

Last Updated: Wednesday 21st May 2014

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