State Highway 1 (New Zealand)

State Highway 1 (SH 1) is the longest and most significant road in the New Zealand road network, running the length of both main islands. It appears on road maps as SH 1 and on road signs as a white number 1 on a red shield, but it has the official designations SH 1N in the North Island and SH 1S in the South Island.

SH 1 is long, in the North Island and in the South Island. Since 2010 new roads have reduced the length from . For the majority of its length it is a two-lane single carriageway, with at-grade intersections and property accesses, in both rural and urban areas. These sections have some passing lanes. Around of SH 1 is of motorway or expressway standard : in the North Island and in the South Island.

Route

North Island (SH 1N) SH 1 starts at Cape Reinga, at the northwestern tip of the Aupōuri Peninsula, and since April 2010 has been sealed (mainly with either chipseal or asphalt) for its entire length. From Waitiki Landing south of Cape Reinga, SH 1 travels down the central-eastern side of the peninsula to Kaitaia, New Zealand's northernmost town, then travels through the Mangamuka Gorge before turning south-east across the Northland Peninsula on to Kawakawa in the Bay of Islands where the roadway is shared by the Bay of Islands Vintage Railway track, and then south to the city of Whangārei, the largest urban area in Northland.

SH 1 then skirts the south-western Whangārei Harbour, nearing the coast briefly at Ruakākā, before proceeding down to wind through the Brynderwyn Hills before approaching the upper reaches of the Kaipara Harbour. The highway crosses into the Auckland Region, passing through Wellsford.

Just north of Warkworth, SH 1 becomes the northernmost section of the Auckland Northern Motorway. This section was opened in 2023 and extends to the Johnstones Hill Tunnels, just south of Puhoi. At this point the motorway becomes the Northern Gateway Toll Road, a section of automated toll road passing the Hibiscus Coast suburbs of Orewa and Silverdale. From Silverdale, the motorway becomes toll-free, crossing farmland to Albany and continuing past suburbs on the North Shore of Auckland. The road crosses over the Waitematā Harbour on the Auckland Harbour Bridge into Auckland's city centre and the Central Motorway Junction. At this junction, SH 1 becomes the Auckland Southern Motorway, and proceeds in a south-easterly direction across the Auckland isthmus, through Manukau and Papakura to the top of the Bombay Hills, just short of the Auckland/Waikato boundary.

At Bombay, SH 1 becomes the Waikato Expressway, a four-lane dual-carriageway expressway. The expressway takes the highway down the Bombay Hills to Mercer, where SH 1 meets the Waikato River, which it broadly follows for the next . The Waikato Expressway bypasses Hamilton city centre to the east, then bypasses Cambridge to the north before reverting to a single carriageway east of the town. The highway continues eastward to the town of Tīrau, where it turns south to pass through Putāruru and Tokoroa and the surrounding exotic pine plantation forest area.

At Wairakei, SH 1 takes an eastern route to bypass Taupō and meet the Lake Taupō shoreline south of the town near the airport. SH 1 follows the eastern shore of the lake for to Tūrangi, at the southern end of the lake. Via SH32/41 the distance is about shorter than this section of SH1.

Turning southwards again, SH 1 leaves Tūrangi and ascends onto the North Island Volcanic Plateau, passing through the fringes of the Tongariro National Park and into the Rangipo Desert, passing the volcanoes of Ruapehu, Ngauruhoe and Tongariro. The road between Rangipo ( south of Tūrangi) and Waiouru is commonly known as the Desert Road. SH 1 enters the Manawatū-Whanganui Region, and descends through an army training area to the end of the Desert Road at Waiouru.

From Waiouru, the highway follows tributaries of the Rangitikei River through Taihape to meet the main river at Utiku. It then follows the western bank of the Rangitikei through Ohingaiti and Hunterville to Bulls. At Bulls, SH 1 turns southeast to cross the river, turning southwest again down the road at Sanson. SH 1 crosses the Manawatū Plains, passing the city of Palmerston North about west of it. It passes through Foxton, before reaching the end of the plain at Levin.

From Levin, SH 1 follows the narrowing western coastal plain southwards. The highway crosses into the Wellington Region south of Levin, and just north of Ōtaki widens into the Kāpiti Expressway, a fully grade-separated four-lane dual carriageway. This expressway bypasses the Kāpiti conurbation of Waikanae, Paraparaumu and Raumati, before reaching the end of the coastal plain at Mackays Crossing. It then becomes the Transmission Gully Motorway and steeply ascends through mountainous terrain to the Wainui Saddle, before descending through its namesake to Pāuatahanui and bypassing Porirua to the east before reaching the northern suburbs of Wellington, New Zealand's capital city.

Immediately after entering the city of Wellington in the suburb of Linden, the Transmission Gully Motorway ends, and SH 1 merges on to the Johnsonville-Porirua Motorway. The motorway gradually ascends through Tawa before reaching Johnsonville. Here, the motorway ends, and SH 1 as a six-lane arterial road steeply descends through the Ngauranga Gorge to the Ngauranga Interchange, on the shore of Wellington Harbour.

At Ngauranga, SH 1 becomes the Wellington Urban Motorway, skirting the shore of the harbour then passing the city centre to the west. The motorway ends at Te Aro, where a one-way system takes traffic to the Basin Reserve. Northbound traffic uses the Wellington Inner City Bypass (opened 2007), while southbound traffic uses Vivian Street. From the Basin Reserve, SH 1 travels through the Mount Victoria Tunnel to Wellington's eastern suburbs and Wellington International Airport. SH 1 ends at a roundabout at the entrance to the airport.

South Island (SH 1S) The South Island section of SH 1 starts in Picton, adjacent to the railway station. Leaving Picton, SH 1 rises steeply to cross the Elevation saddle into the valley of the Tuamarina River. It descends alongside this river and across the Wairau Plain before reaching Blenheim. SH 1 passes through Weld Pass and Dashwood Pass to enter the Awatere Valley, then continues southward before passing Lake Grassmere. From the small town of Ward the highway heads to the coast and follows it to Kaikōura. After passing Kaikōura, it veers inland, twisting through the Hundalee Ranges before emerging at the northern end of the Canterbury Plains.

The section of highway between the Clarence River and Hapuku Rivers north of Kaikōura was closed from 14 November 2016 to 15 December 2017, due to damage from the 2016 Kaikōura earthquake.

SH 1 passes through Amberley and Woodend before becoming the Christchurch Northern Motorway and bypassing Kaiapoi to the west. At The Groynes west of Belfast, the motorway narrows to a four-lane divided arterial. SH 1 continues around the north-western urban fringe of Christchurch, passing just east of Christchurch International Airport. At Hornby, the highway turns south-west, narrows to a two-lane undivided road and passes through Templeton. It then merges onto the Christchurch Southern Motorway where the highway becomes expressway standard until it approaches Rolleston.

South of Rolleston, SH 1 becomes virtually straight as it crosses the wide fan of the Canterbury plains, crossing the country's longest road bridge at Rakaia before reaching Ashburton, and then veering back towards the coast, which it reaches at Timaru. Between Ashburton and Timaru it crosses Rangitata Island in the Rangitata River.

South of Timaru, the road again passes through gentle hill country, staying close to the coast but largely out of sight of it. The road veers inland briefly, bypassing Waimate as it reaches the plains around the mouth of the Waitaki River, which it crosses to enter Otago. It passes through Oamaru, from where it turns inland briefly, crossing undulating hill country before again reaching the coast at Moeraki. From here the road again hugs the coast along Katiki Beach, remaining closer to the ocean than at any point since Kaikōura. The highway turns inland at Shag Point, passing through Palmerston and Waikouaiti.

South of Waikouaiti the road again becomes steep, rising sharply over the Kilmog hill before dropping down to the coast at Blueskin Bay, then rising again via Dunedin-Waitati Highway (a two- to four-lane carriageway which used to be designated a motorway) to the northern outskirts of Dunedin. From here it descends a steep, twisting stretch of Pine Hill Road through Pine Hill, before passing the University of Otago and heading through the city centre. For much of its route through Central Dunedin the highway is split into two separate northbound and southbound roads, part of the city's one-way street system. These roads traverse the central city 2–3 blocks southeast of the heart of the CBD. At the southern end of central Dunedin, the highway becomes the Caversham By-pass, which rises along the Caversham Valley before again becoming a motorway at the saddle of Lookout Point.

The four-lane motorway (Dunedin Southern Motorway) runs through Dunedin's southern suburbs until the interchange with SH 87 at Mosgiel. SH 1 then heads southwest across the Taieri Plains. The area between the Taieri and Waipori Rivers is flood-prone, and the highway crosses this on a major embankment known colloquially as the flood-free highway. SH 1 continues through gentle hill country and along the shore of Lake Waihola, then crosses the Tokomairiro Plains into Milton. South of Milton is a major junction with SH 8 at Clarksville Junction. SH 1 continues to cross rolling hill country to reach Balclutha.

From Balclutha, the highway turns west, veering briefly north as it heads inland to avoid the rough hills of The Catlins. It passes through the small town of Clinton before reaching the major provincial town of Gore. Because of the names of these two towns, this stretch of the highway was christened "The Presidential Highway" during the time of the Clinton-Gore administration in the United States. At Gore, the highway crosses the Mataura River; from here the road again turns south to roughly follow the river. The highway passes through Mataura before turning west at Edendale. Many travellers choose to turn onto SH 93 at Clinton, as this route shortens the journey between Clinton and Mataura by about and bypasses Gore. Over its last stretch the road veers southwest before reaching the city of Invercargill. In central Invercargill it meets the southern end of and turns due south, skirting the estuary of the New River and Bluff Harbour. It passes through the small town of Bluff before reaching its terminus at Stirling Point, a kilometre south of Bluff. A commemorative signpost at Stirling Point indicates distances to major world centres and to the start of the highway at Picton.

Spur sections

SH 1 has two spurs, both in the vicinity of Hamilton:

SH 1B runs from SH 1N at Taupiri to SH 1N at Cambridge, and provides an eastern bypass of Hamilton. Gazetted in 1999, the highway utilises many roads which were previously under the administration of the Waikato District Council. Part of the highway also shares a concurrency with SH 26. Recent progress of construction of the Waikato Expressway at Ngāruawāhia and Cambridge have also resulted in the curtailment of SH 1B at both the northern and southern termini. SH 1B is to be handed back to the Waikato District Council after the completion of the Hamilton section of the Waikato Expressway in 2022. Because it was not intended to be a permanent state highway, there are intersections where the state highway gives priority to local roads in several places.