Tawa Flat deviation

The NIMT Tawa Flat Deviation's double track climbing towards Tawa No. 1 tunnel over the up Wairarapa Line and Hutt Rd, with Ngauranga station in the background alongside the State Highway 1 motorway.

The Tawa Flat deviation is a double-track section of the North Island Main Trunk Railway (NIMT) just north of Wellington, New Zealand. It was built to bypass the original Wellington & Manawatu Railway line up to Johnsonville and then back down to Tawa. The original name of Tawa Flat had been changed to Tawa in 1959.^[1]

The deviation includes two long tunnels, Tawa No. 1 (1,238 metres (4,062 ft)) and Tawa No. 2 (4,323 metres (14,183 ft)), separated by the Ngauranga Gorge. No. 2 tunnel passes under Newlands and comes out at Glenside, on the way to Tawa Flat. The tunnels were constructed by the Public Works Department as no satisfactory tenders were received. South of the Tawa No. 1 tunnel a flyover was constructed over the two tracks of the Wairarapa Line. The current configuration (as shown in the photo at right) was adopted when the down Wairarapa track was moved to the east when the Wellington Urban Motorway was constructed. This also removed junction conflicts further south.

The deviation opened to goods trains on 22 July 1935 and to passengers on 19 June 1937.^[2]

The line from Wellington to Paekakariki was electrified at 1500 V DC from 24 July 1940, being delayed by late delivery of some items from England. Initially locomotive-hauled trains were used, and DM/D electric multiple units first ran on the line on 5 September 1949.^[3] As was pointed out in the 1925 Merz & McLellan Report, electrification removed the need to relieve the steep gradients to the Pukerua Bay summit by a deviation to the east, and was desirable in the long No. 2 tunnel. ED class electric locomotives were introduced in 1938 for use on this section. The electrification was extended further north in 1983 to Paraparaumu and then in 2011 to Waikanae.

External links

• 1927 article with graphs

References

1. ↑ Carman, A. H. (1970, also 1956, 1982). Tawa Flat and the Old Porirua Road. Wright and Carman. p. 235.  Check date values in: |date= (help)
2. ↑ Murray and Parsons, pp. 30,33
3. ↑ Murray and Parsons, p. 36

• North Island Main Trunk: An Illustrated History by W.A. Pierre (1981, A.H. & A.W. Reed), ISBN 0-589-01316-5.
• Rails through the Valley: The story of the construction and use of the railway lines through Tawa by Bruce Murray and David Parsons (2008, Tawa Historical Society) ISBN 978-0-473-14410-4