New Zealand State Highway 20

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State Highway 20 NZ.svg

State Highway 20
Southwestern Motorway
Route information
Maintained by New Zealand Transport Agency
Length: 19 km (12 mi)
Existed: 1977 – present
Major junctions
South end: State Highway 1 NZ.svg SH 1 Southern Motorway at Manukau City Centre
  SH 20B at Puhinui
SH 20A at Mangere
North end: Sandringham Road/Maioro Street at Mount Roskill
Highway system
SH 18 SH 21
Aerial view of the interchange between SH20 (diagonal from bottom left to upper right) and SH20A towards the airport (towards bottom right).

State Highway 20, also known as the Southwestern Motorway, is a New Zealand State Highway linking State Highway 1 at Manukau City Centre with Mount Roskill, via Mangere and Onehunga. Along with its spurs, State Highway 20A and 20B, the state highway serves Auckland Airport, the country's largest, therefore making State Highway 20 a key arterial route connecting the airport to the wider Auckland region and most of the upper North Island. The route also forms the southern part of the Western Ring Route, a 48 km motorway route bypassing central Auckland.


SH20 stretches from the Auckland Southern Motorway / New Zealand State Highway 1 at Manukau to Sandringham Road, Sandringham, in Auckland City. From south to north the motorway passes through, or adjacent to, the suburbs of Wiri, Mangere, Onehunga, Hillsborough and Mount Roskill.

Airport connection

The Southwestern Motorway bypasses Auckland International Airport, with SH20A from the north and SH20B from the east both branching off the SH20 to the airport.

SH20B leaves SH20 at the Cavendish Dr/Puhinui Rd/Roscommon Rd Interchange of the Southwestern Motorway and travels west along Puhinui Road to the airport. SH20A leaves the Southwestern Motorway in Mangere and travels south along an additional stretch of motorway, commonly referred to as the "Airport Motorway". The motorway terminates at Kirkbride Road, and traffic continues on SH20A south to the airport.

SH20, SH20A, and SH20B form an almost triangular shape between the Puhinui Interchange of the Southwestern Motorway, Auckland International Airport, and the SH20/SH20A motorway junction.

The planned final terminus will be the Northwest Motorway / New Zealand State Highway 16 via the Waterview Connection scheduled to open in 2017.[1]


The first section of what would become the Southwestern Motorway was the Onehunga Bypass from Queenstown Road, Hillsborough to Neilson Street, Onehunga but the start of the motorway proper was not completed until 1983 when the bypass was connected through the new Mangere Bridge to Coronation Road, Mangere.

The northern section was extended first to Hillsborough Road, then to Hayr Road, then to Maioro Street, the last section opening on 15 May 2009.[2]

The southern section was extended to Puhinui Road in 1997, along with the extensions SH20A and SH20B connecting to Auckland International Airport. The final southern section connecting Puhinui Road to State Highway 1 at Manukau was completed in 2010.[3] A duplication of Mangere Bridge, with future provision for rail, was also opened in 2010.[4]


The final section of the Southwestern Motorway, the Waterview Connection, will connect the current western terminus of State Highway 20 at Maioro Street with State Highway 16 at the Great North Road Interchange. Construction of this section began in 2012 and is due for completion in 2017.[1]

Proposals to upgrade State Highway 20A as part of a general route upgrade to the airport have been floated in a number of studies.

Exit list[edit]

Territorial authority Location km Exit Destinations Notes
Former Current (from 1 Nov 2010)[5]
Manukau City AucklandOtara-Papatoetoe/Manurewa Boards Manukau CBD 0.0 State Highway 1 NZ.svg SH 1 Southern Motorway south — Hamilton, Tauranga SH 20 and Southwest Motorway end
1 State Highway 1 NZ.svg SH 1 Southern Motorway north — Auckland
2 Lambie Drive — Manukau, Wiri
Puhinui 3 Route 30 Cavendish Drive/Roscommon Road - Manukau, Wiri No southbound exit (use Puhinui Road)
Northbound entrance and connection to SH 20B and BSicon FLUG.svg
AucklandOtara-Papatoetoe Board Puhinui 3 BSicon FLUG.svg SH 20B Puhinui Road — Airport, Papatoetoe No northbound exit (use Cavendish Drive)
Southbound entrance and connection to SH 20B and BSicon FLUG.svg
AucklandMangere-Otahuhu Board Mangere 7 Route 14 Massey Road - Mangere
9 BSicon FLUG.svg SH 20A — Airport No southbound entrance (use SH20B or Massey Road)
Carriageway mainline connects north to west, traffic proceeding from/to south on motorway must 'exit'.
10 Walmsley Road Southbound
Coronation Road Northbound
Mangere Bridge 12 Mahunga Drive — Mangere Bridge Southbound exit and northbound entrance
Mangere Bridge over Manukau Harbour
Auckland City AucklandMaungakiekie-Tāmaki Board Onehunga
13 Neilson Street — Onehunga Wharf, Onehunga, Penrose, Mt Wellington
AucklandMaungakiekie-Tāmaki/Puketapapa Boards Hillsborough 15 Route 12 Queenstown Road — Epsom, Royal Oak, Auckland CBD Northbound exit and southbound entrance
AucklandPuketapapa Board 16 Route 15 Hillsborough Road - Hillsborough, Blockhouse Bay
Mount Roskill 18 Route 4 Dominion Road - Mount Roskill
Maioro Street - New Lynn, Sandringham SH 20 and Southwest Motorway end
1.000 mi = 1.609 km; 1.000 km = 0.621 mi

See also[edit]


External links[edit]