New Zealand State Highway 20
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|Maintained by NZ 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:||Maioro Street at New Windsor|
State Highway 20, also known as the Southwestern Motorway, is a New Zealand State Highway linking State Highway 1 at Manukau City Centre with Maioro Street in 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.
SH 20 stretches from the Auckland Southern Motorway / State Highway 1 at Manukau to Maioro Road. From south to north the motorway passes through, or adjacent to, the suburbs of Wiri, Mangere, Onehunga, Hillsborough and Mount Roskill.
The motorway (and SH 20) currently terminates at Maioro Street. The planned final terminus will be the Northwest Motorway / New Zealand State Highway 16 via the Waterview Connection scheduled to open in early 2017.
SH 20, SH 20A, and SH 20B form an almost triangular shape between the Puhinui Interchange of the Southwestern Motorway, Auckland International Airport, and the SH 20/SH 20A motorway junction. The Southwestern Motorway bypasses Auckland International Airport, with spurs SH 20A from the north and SH 20B from the east both providing airport access.
SH 20B leaves SH 20 at the Cavendish Dr/Puhinui Rd/Roscommon Rd Interchange of the Southwestern Motorway and travels west along Puhinui Road to the airport, officially terminating at the intersection with Orrs Road. SH 20A 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 SH 20A terminating just north of the roundabout with Verissimo Drive. From there the road continues south to the airport. A construction project is underway in 2015–17 to turn SH 20A into a motorway for its entire length by turning the intersection at Kirkbride Road (and a known black spot) into a grade-separated intersection.
The first section of what would become the Southwestern Motorway was the Onehunga Bypass from Queenstown Road in Hillsborough to Neilson Street in 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 in 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 SH 20A and SH 20B 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 early 2017.
|Auckland — Otara-Papatoetoe/Manurewa Boards||Manukau CBD||0.0||1||SH 1 Southern Motorway south — Hamilton, Tauranga||SH 20 and Southwest Motorway begins|
|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||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||Right-hand southbound exit and northbound entrance.
No southbound entrance (use SH20B or Massey Road)
|Mangere Bridge||12||Mahunga Drive — Mangere Bridge||Southbound exit and northbound entrance|
|Mangere Bridge over Manukau Harbour|
|Auckland — Maungakiekie-Tāmaki Board||Onehunga|
|13||Neilson Street — Onehunga Wharf, Onehunga, Penrose, Mt Wellington|
|Hillsborough||15||Route 12 Queenstown Road — Epsom, Royal Oak, Auckland CBD||Northbound exit and southbound entrance|
|Auckland — Puketāpapa Board|
|16||Route 15 Hillsborough Road - Hillsborough, Blockhouse Bay|
|Mount Roskill||18||Route 4 Dominion Road - Mount Roskill|
|19.7||19||Maioro Street - New Lynn, Sandringham||SH 20 and Southwest Motorway ends|
|Auckland — Albert-Eden Board||Waterview||23.8||24A||SH 16 Northwestern Motorway west — Helensville, Wellsford||Waterview Connection. Expected to be open April 2017. Will become the new terminus for SH 20.|
|24B||SH 16 Northwestern Motorway east — Auckland|
|1.000 mi = 1.609 km; 1.000 km = 0.621 mi
- "Waterview Connection". NZTA.
- "SH20A to Airport". NZ Transport Agency. Retrieved 10 December 2016.
- Dearnaley, Mathew (18 May 2009). "Another piece slots into city's commuter jigsaw". The New Zealand Herald. Retrieved 5 March 2010.
- "SH20-1 Manukau Extension". NZTA.
- "Western ring route progressing". The New Zealand Herald. 7 June 2010. Retrieved 9 July 2010.
- "Mangere Bridge Opened Today". The New Zealand Herald. 25 July 2010. Retrieved 1 August 2010.