In the late 1960s, reclamation work began to the east of the 1960 rail reclamation from Porirua to Paremata allowing the construction of a four-lane expressway alongside the railway. The expressway opened in the early 1970s with room allowed for a future interchange at Whitford Brown Avenue. The reclamation work largely eliminated the north and south lagoons created by the rail reclamation on the east side of the harbour and reduced the size of the central lagoon, known as Aotea Lagoon. An intersection between SH1 and Mungavin Avenue remained at Porirua until 1989 when the intersection was replaced with a grade-separated roundabout interchange with State Highway 1 passing under the interchange.