Steam as a form of motive power is far from dead on the New Zealand Railways, although no new steam locomotives have been built for the service since 1956. Today the powerful diesel-electric locomotive is gradually ousting steam. In some respects this is to be regretted, for the New Zealand Railways have a long and proud tradition of steam locomotive design and construction. In 1889 the railway workshops built their first locomotive, a 37-ton tank engine of class “W”, and it was a New Zealand designer who gave the world the first “Pacific” (4–6–2) and “Mountain” (4–8–2) type locomotives, in 1901 and 1908 respectively. The latest types of steam locomotive in New Zealand, the 4–8–2 “Ja”, weighing 110 tons, and the 4–8–4 “Ka”, weighing 145 tons, are magnificent and thoroughly modern machines which have done sterling work both in passenger and in freight service. Designed in New Zealand for local conditions, they nevertheless reveal traces of their British and American ancestry. A “Ka” is capable of hauling a 13-car, 400-ton express train at well over a mile a minute on level track, or a 1,000-ton freight train at 30 m.p.h. The speedy and graceful “Ja” has demonstrated its remarkable performance in express service on the level plains of Canterbury, and on occasions has attained speeds in excess of 70 miles an hour.

At the end of March 1965 New Zealand Railways had in operation 57 oil-fired and 260 coal-fired steam locomotives; 159 diesel-electric main line and 46 diesel-electric shunting locomotives; 148 diesel-mechanical shunting locomotives; and 28 electric locomotives. Diesels are responsible for working almost all freight traffic over the North Island Main Trunk line. Moreover, the use of diesel shunting locomotives in marshalling yards and at country stations has resulted in the withdrawal of large numbers of obsolete steam locomotives. In addition, freight services have been greatly improved in recent years. Goods trains are now carrying heavier payloads and are moving faster, with distinct savings in fuel and wages. On the Wellington-Auckland route alone, the use of diesel locomotives has enabled ordinary goods train schedules to be reduced from 38 hours to less than 24 hours. Four principal types of diesel-electric main-line locomotives are in use: the General Motors G-12 type of 1,425 b.h.p., otherwise known as class “Da”; the English Electric 1,500 b.h.p. 2–Co–Co–2 of class “Df”; the English Electric 750 b.h.p. A1A–A1A of class “Dg”; and the English Electric 660 b.h.p. Bo–Bo of class “De”. Two new types of diesel-electric locomotive recently introduced for service on secondary main lines are the General Motors G-8 A1A–A1A type of 950 h.p., classified “Db”, and the English Electric Co–Co type of 1,012 h.p., which are known as class “Di”.

Diesel power has also played an important part in the improvement of railway passenger services in New Zealand. Fifty diesel railcars are in use, providing fast and frequent services over practically all principal inter-city routes. The first diesel railcars in New Zealand were placed in service as early as 1936–37, and in 1940 a new type then on test attained 78 m.p.h., the highest speed ever officially recorded on New Zealand Railways.

Electrification has not made its mark in New Zealand to the extent that might have been expected in a country with considerable hydro-electric power-generating resources. Only five sections of line, with a total route length of 68 miles, have been electrified, and at first the principal reason was the undesirability of using steam locomotives through long tunnels. Some years ago comprehensive plans were drawn up for the electrification of the North Island Main Trunk line between Paekakariki and Auckland, but diesel traction, introduced as a stop-gap measure to avoid heavy capital expenditure, proved that it could cope with all the traffic offering. As a result the electrification proposals were shelved.

The electrified sections at present in use work at a line pressure of 1,500V d.c., current being collected by pantograph from an overhead contact wire. The earliest installation was completed in 1923 between Otira and Arthur's Pass, through the Otira Tunnel. In 1929, after more than 60 years of steam operation, the Christchurch-Lyttelton line was electrified to improve passenger travel through the Lyttelton Tunnel. Electrification of the Wellington suburban railway network began a few years before the 1939–45 war. The first section, completed in 1938, was the steeply graded branch line from Wellington to Johnsonville, this being followed two years later by the 25-mile Wellington-Paekakariki section of the Main Trunk line. In 1955, after several years of work involving the construction of new tracks, stations, and bridges, the Wellington – Upper Hutt section (20 route miles) was completed at a cost of nearly £5 million. This brought the aggregate length of electrified routes radiating from Wellington to more than 50 miles.

Average Tractive Effort Per Locomotive