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. During peak periods many multiple unit trains were now terminated at Porirua and returned to Wellington to provide a more frequent service between Wellington and Porirua than was provided for stations north of Porirua.