Between Paekākāriki and Pukerua Bay, SH 1 and the North Island Main Trunk rail line travel along a narrow strip of land between the hills and the sea. The Centennial Highway, as it is known, is a narrow two-lane road that was highly accident prone until a centreline wire rope crash barrier was installed. Travelling through Pukerua Bay, the road becomes dual carriageway once more to Plimmerton, narrowing to single carriageway through the northern suburbs of Porirua to Paremata. The route will be diverted east in 2020 upon the opening of the Transmission Gully Motorway.