||This article needs additional citations for verification. (August 2010)|
|Maintained by New Zealand Transport Agency|
|Length:||19 km (12 mi)|
|Existed:||1977 – present|
|South end:||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|
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 in Manukau City 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 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.
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. A duplication of Mangere Bridge, with future provision for rail, was also opened in 2010.
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.
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 
|Former||Current (from 1 Nov 2010)|
|Manukau City||Auckland — Otara-Papatoetoe/Manurewa Boards||Manukau CBD||0.0||SH 1 Southern Motorway south — Hamilton, Tauranga||SH 20 and Southwest Motorway end|
|1||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
|Auckland — Otara-Papatoetoe Board||Puhinui||3||SH 20B Puhinui Road — Airport, Papatoetoe||No northbound exit (use Cavendish Drive)
Southbound entrance and connection to SH 20B and
|Auckland — Mangere-Otahuhu Board||Mangere||7||Route 14 Massey Road - Mangere|
|9||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'.
|Mangere Bridge||12||Mahunga Drive — Mangere Bridge||Southbound exit and northbound entrance|
|Mangere Bridge over Manukau Harbour|
|Auckland City||Auckland — Maungakiekie-Tāmaki Board||Onehunga|
|13||Neilson Street — Onehunga Wharf, Onehunga, Penrose, Mt Wellington|
|Auckland — Maungakiekie-Tāmaki/Puketapapa Boards||Hillsborough||15||Route 12 Queenstown Road — Epsom, Royal Oak, Auckland CBD||Northbound exit and southbound entrance|
|Auckland — Puketapapa 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|
See also 
- Auckland Motorways - The Waterview Connection
- Dearnaley, Mathew (18 May 2009). "Another piece slots into city's commuter jigsaw". The New Zealand Herald. Retrieved 5 March 2010.
- Auckland Motorways - Manukau Extension
- "Western ring route progressing". The New Zealand Herald. 7 June 2010. Retrieved 9 July 2010.
- "Auckland Governance Arrangements: Maps relating to Determinations of Wards, Local Boards and Boundaries for Auckland". Local Government Commission. March 2010. Retrieved 2010-07-10.
- "Mangere Bridge Opened Today". The New Zealand Herald. 25 July 2010. Retrieved 1 August 2010.
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