Metlink's Kapiti Line is the electrified southern portion of the North Island Main Trunk railway between New Zealand's capital city, Wellington, and Waikanae on the Kāpiti Coast, operated by Transdev Wellington on behalf of Greater Wellington Regional Council. Trains run frequently every day, with stops at 16 stations. Until 20 February 2011 it was known as the Paraparaumu Line.
Construction
The Kapiti Line was constructed by the Wellington and Manawatu Railway Company (W&MR) as part of its line between Wellington and Longburn, south of Palmerston North. It was built by a group of Wellington businessmen frustrated with the indecision of the government about the construction of a west coast route out of Wellington.
Construction of the line began in September 1882 and followed a circuitous, steep route via Johnsonville. It was opened to Plimmerton in October 1885 and completed on 3 November 1886. The final spike was driven just north of Paraparaumu, at Otaihanga.
The government acquired the Wellington and Manawatu Railway Company on the 7 December 1908 and incorporated it into its national network as the southern portion of the North Island Main Trunk line.
Deviation and electrification
In 1928, work began on a deviation to avoid the difficult section of the line between Wellington and Tawa through Johnsonville. The deviation required the construction of two significant tunnels between Kaiwharawhara and Tawa. It opened as a single track line to freight on 24 July 1935 and as a double track line to passengers on 19 June 1937. The Wellington to Johnsonville section was retained as the Johnsonville Line.
Electrification from Wellington to Paekakariki was completed on 24 July 1940, avoiding the smoke nuisance in the new deviation's lengthy second tunnel, and providing extra tractive effort on the Paekakariki Hill between Pukerua Bay and Paekakariki. Paekakariki became a major station where long-distance trains swapped from steam (later diesel) to electric motive power and became the northern terminus of the commuter line for many years. Electrification was extended to Paraparaumu on 7 May 1983 and to Waikanae on 20 February 2011.
Duplication
The W&MR constructed the line as a single-track railway with crossing loops at principal stations to allow opposing trains to pass. In the 1920s the need for extra train services on the line was recognised, both to increase the tonnage of goods trains and to allow more frequent suburban passenger services. To increase the number of trains that the line could carry, duplication and electrification of the line along with other improvements, such as curve easements, was planned and progressed in stages. The first section to bed double-tracked (from Wellington to Tawa Flat (now Tawa) was the Tawa Flat deviation. it bypassed the steep (1 in 36 to 40) grades from Wellington to Ngaio on the Johnsonville Line. The sections from Tawa to Porirua and subsequently from Porirua to the Pukerua Bay saddle were later double-tracked.
As part of the Plimmerton to Paekakariki duplication, a Westinghouse three-wire (two feed and one return) Centralised Train Control (CTC) system was installed in 1940; to control trains from Wellington. It was the first CTC system in New Zealand and the first outside the United States of America. This avoided the need for two new signal boxes at the North and South junctions and the need with "tablet" working to continuously man five stations with 3 or 4 tablet porters at each station (3 tablet porters at Porirua, Paremata and Pukerua Bay; and 4 tablet porters at Tawa Flat and Plimmerton); so requiring 19 men for traffic working instead of 8 with CTC (and also 11 staff houses). CTC working applied between Paekakariki and Plimmerton on 25 February, Plimmerton and Paremata on 30 June and Tawa to Porirua on 4 December 1940; giving full traffic control from Wellington to Paekakariki (as Wellington to Tawa was double-tracked).
From 14 June 1943 a siding for the US Marines' camp at Mackays Crossing with a crossing loop and tablet station was opened; near where the Wellington Tramway Museum is now located. With duplication of the track from Paekakariki to Mackays Crossing and automatic signalling from Paekakariki to Paraparaumu, Mackays Crossing was relay worked from the Paekakariki South signal box from December 1943. But on 25 March 1946 the catch points and two cross-overs of the siding were lifted, and Mackays Crossing became the point where the double-track section north ended.