Tawa Flat deviation
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The Tawa Flat deviation is a double-track section of the North Island Main Trunk Railway (NIMT) just north of Wellington, New Zealand. It includes two tunnels, Tawa No 1 (1238 m) and Tawa No 2 (4323 m), separated by the Ngauranga Gorge. No 2 tunnel passes under Newlands and comes out at Glenside, on the way to Tawa. It replaced a steep section of the main line of the former Wellington & Manawatu Railway Company, most of which is still in use as the Johnsonville Branch.
It is used by Tranz Metro services to Porirua and Paraparaumu, by Tranz Scenic's Overlander and Capital Connection, and by Toll Rail freight trains.
The tunnels were constructed by the Public Works Department as no satisfactory tenders were received.
The deviation opened to goods trains on 24 July 1935 and to passenger trains on 19 June 1937. The section from Wellington to Paekakariki was electrified using the 1500 V DC system from July 1940, being delayed by late delivery of some items from England. As was pointed out in the 1925 Merz & McLellan Report, electrification removed the need to relieve the steep gradients to Pukerua Bay summit by a deviation to the east, and was desirable in the long No 2 tunnel. The ED class electric locomotives were introduced in 1938 for use over this section.
Congestion on this section of the NIMT was shifted north, and in 1961 duplication north from Tawa to Porirua and Plimmerton was completed. The work included a new bridge over the Porirua Harbour inlet and straightening the line along Porirua Harbour by reclamation.
Tawa Flat was renamed Tawa about 1955.
[edit] References
North Island Main Trunk: An Illustrated History by Bill Pierre (1981, AH & AW Reed), ISBN 0 589 01316 5.
