The first section of the Northwestern Motorway, from Waterview to Te Atatū, was finished in 1952. The section between Waterview and Rosebank peninsula is known as "The Causeway". The next section opened for traffic in 1955, then offering a two-laned 7.8 km section from Great North Road to Lincoln Road. The section involved bridges over inlets of the Waitematā Harbour, which cut the journey between central Auckland and its airport at Whenuapai by 8 km. This section was later upgraded to four lanes. In 1957, the motorway was extended westwards by one km to Lincoln Park Avenue, between the current Lincoln Road and Royal Road interchanges. In 1961, it was extended again by 2.7 km to Hobsonville Road at what is now Westgate. Traffic could now travel 11.5 km on the Northwestern Motorway, and the journey between Auckland and Whenuapai was cut by a total of 9 km compared with local roads. In 1966, the current Auckland International Airport opened at Mangere, and Whenuapai reverted to a military airport. This affected the use of the motorway, delaying further extensions. Motorway construction recommenced in the late 1970s, to connect the Northwestern Motorway at Waterview to the Auckland city centre, bypassing Great North Road. The first section to open was in 1979, stretching 2.4 km from Newton Road to Western Springs, at the current site of the eastbound on/off-ramps for St Lukes Road. At the same time, ramps opened as part of the Central Motorway Junction from Newton Road to Nelson Street and Hobson Street, connecting the Northwestern Motorway to the city centre. Traffic could access the Southern and Northern Motorways indirectly from the Nelson Street and Hobson Street intersections. In 1981, the 2.4 km section between Great North Road at Waterview and Motions Road near Western Springs opened, leaving a small 1 km gap where traffic had to use Great North Road. This gap was filled in 1983 when the St Lukes Road interchange was completed. In 1988, ramps were installed at the Central Motorway Junction to allow direct access between the Southern Motorway and the Northwestern Motorway. The following year, ramps opened between Grafton Gully and the Northwestern Motorway, allowing motorway traffic direct access to the eastern city centre and the port. In 2006, two new ramps were installed to directly connect the Northwestern Motorway and the Northern Motorway. On 7 August 2011 a 3 kilometre, 4-lane extension of the Northwestern Motorway opened from Hobsonville Road to Brigham Creek Road in Whenuapai, along with a 6 kilometre, 4-lane extension of State Highway 18 motorway from the end of the Northwestern Motorway at Hobsonville Road to the western end of Upper Harbour Bridge in Hobsonville. From 2012 to 2016 extra lanes were added between St Lukes and Westgate in preparation for the opening, on 2 July 2017, of the Waterview Connection.
