 The duplication of the line from Plimmerton to South Junction allowed a more frequent train service between Porirua and Paekakariki

Duplication of the track from Tawa to Porirua station opened on 15 December 1957.This completed double line automatic signalling from Wellington distant junction, just south of Kaiwharawhara, to Porirua, and eliminated CTC between Tawa and Porirua.This work, and the provision of additional signals between Kaiwharawhara and Tawa allowed close following of trains and more frequent and faster train services between Wellington and Porirua.