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State Highway 1
Length	2047 km 1272 mi
Primary direction	North-South
Start	Cape Reinga
Primary destinations	Whangarei North Shore Auckland Manukau Hamilton Taupo Porirua Wellington Picton Blenheim Christchurch Ashburton Timaru Oamaru Dunedin Invercargill
End	Bluff
Route quality	89% single carriageway 5% dual carriageway 6% motorway
Tourist routes	Twin Coast Discovery Highway Awanui to Kaitaia Kawakawa to Waipu Brynderwyn to Auckland Thermal Explorer Highway Auckland to Tirau Wairakei to Taupo Great New Zealand Wine Trail Picton to Blenheim Alpine Pacific Triangle Kaikoura to Waipara Southern Scenic Route Waihola to Balclutha Invercargill

State Highway 1 is the most significant road in the New Zealand roading network. It runs the length of both main islands State Highway 1 officially has two designations: SH 1N in the North island and SH 1S in the South Island, but both sections appear on road signs and road atlases as SH1. It is 2047 km long, 1106 km in the North Island and 941 km in the South Island. Distances are measured from north to south in each island.

For most of its length SH1 is a two-lane single carriageway, with at-grade intersections and property accesses, both in rural and urban areas. These sections have frequent passing lanes. There are sections of motorway in the vicinity of Auckland, Wellington, Christchurch and Dunedin. It is likely that more of SH1 will be rebuilt to motorway or expressway standards.

This is the route that SH1 takes in 2007.

State Highway 1 in South Auckland.

In the North Island, the start point is at Cape Reinga. The first 20 km are unsealed. From Waitiki Landing, it tends to follow the eastern side of the Northland Peninsula, passing through Kaitaia, Whangarei, Wellsford, and Warkworth to Orewa, where it becomes the Auckland Northern Motorway, later crossing the Auckland Harbour Bridge into Auckland. This section is the busiest and most congested road in the country with the major motorway junction (known as the Central Motorway Junction or Spaghetti Junction) between SH1 and SH16 carrying over 200,000 vehicles per day in March 2006.

From Auckland the motorway continues south, known as the Auckland Southern Motorway, changing into a four-lane divided expressway 50 km south of the Harbour Bridge. Just beyond this point SH2 branches off to the east while SH1 continues south to Mercer, from where it follows the course of the Waikato River through Hamilton. Here SH3 branches off to the southwest and SH1 turns southeast towards Cambridge and past Lake Karapiro. A $650 million project to convert the 160 km between Auckland and Cambridge to a four-lane divided carriageway (known as the Waikato Expressway) was about 50% complete at the beginning of 2006. At Tirau, SH5 starts and travels eastward towards Rotorua, while SH1 turns south, passing through Tokoroa and extensive tracts of plantation forest to Taupo on the northeastern shore of Lake Taupo. It skirts the lake's eastern shore before reaching Turangi, near the south end of the lake.

South of Turangi it crosses the North Island Volcanic Plateau and the Rangipo Desert to Waiouru, known as the Desert Road and frequently closed by snow in winter. At the Desert Road summit it is 1074 m above sea level, the highest point in the New Zealand State Highway network. There are spectacular views of the three volcanoes Mount Tongariro, Mount Ngauruhoe and Mount Ruapehu. From Waiouru it descends to Taihape and Mangaweka, veering southwest along the course of the Rangitikei River. SH3 shares its route for the six-kilometre stretch between Bulls and Sanson on the Manawatu Plain, before reaching Foxton and Levin.

South of Levin it follows the narrowing western coastal plain through Otaki, Paekakariki and Plimmerton. Difficult terrain and a large number of satellite towns make this an area of considerable congestion and a high number of accidents. It becomes the Johnsonville-Porirua Motorway at Porirua, travelling through Wellington's northern suburbs. At the end of the Johnsonville-Porirua Motorway at Newlands, SH1 becomes Centennial Highway through the Ngauranga Gorge. Two kilometres later, at the SH1/SH2 Ngauranga interchange, SH1 becomes the Wellington Urban Motorway. The motorway ends at Willis St, and SH1 continues to the eastern suburbs, where it terminates at a roundabout at the entrance to Wellington International Airport.

Ferries cross Cook Strait from the capital to Picton in the Marlborough Sounds. There have been calls for the ferries to be classified as part of the State Highway network, in the belief that this would increase the Government's powers to intervene and keep them running at times of industrial action.

In Dunedin, the highway becomes two multi-lane one-way streets. Here, traffic moves south along SH1 via Cumberland Street, one kilometre south of the city centre.

From the Picton ferry terminal SH1 is steep, crossing a saddle into the valley of the Tuamarina River. It descends alongside this river and across the Wairau Plain before reaching Blenheim. From here it largely hugs the coast, passing the foot of the steep Kaikoura Ranges. This stretch is one of the most scenic, with the Pacific Ocean on one side and 2500-m peaks on the other. Passing Kaikoura it veers inland, twisting tortuously through the Hundalee Ranges before emerging at the northern end of the Canterbury Plains.

It passes through Amberley before becoming the Christchurch Northern Motorway, bypassing Kaiapoi. The motorway ends just north of Styx, and SH1 bypasses Christchurch to the west. South of Christchurch it 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.

From Timaru it follows the coast, crossing the Waitaki River and reaching Oamaru before crossing the undulating hill country of north Otago. South of Waikouaiti it again becomes steep, rising sharply over the Kilmog hill before dropping down to the coast, then rising again and becoming motorway (2/3-lane single carriageway) to the northern outskirts of Dunedin, where it descends steeply, past the University of Otago and through the city centre. For much of its route through Dunedin, the highway is split into two separate roads, a northbound road and a southbound road, which are part of the city's one-way street system. A four-lane motorway runs through Dunedin's southern suburbs until the junction with SH87 at Mosgiel. SH1 then heads southwest to Balclutha before turning west to avoid the rough hills of The Catlins, turning south again at Gore. From Gore it runs south and then southwest to Invercargill, thence to Stirling Point, a kilometre south of Bluff.

Since Transit New Zealand took control of State Highways in 1989, SH1's route has changed in some places. Here are some of them.

In Whangarei, Hamilton, Christchurch and Timaru, it ran through the city centres. It has been diverted to the suburbs, and the original routes have returned to being local roads, or in case of Christchurch, renumbered. The extension of the Dunedin Southern Motorway has also seen changes in the highway, notably to bypass the town of Fairfield.

In the southern South Island, several particularly twisty sections of SH1 have been rebuilt to remove sharp bands and to generally improve road conditions. These include stretches at Waianakarua; at Tumai, near Palmerston; and on the Dunedin Northern Motorway near Waitati.

State Highway 1 has two spurs in the North Island: State Highway 1A and State Highway 1B. State Highway 1A runs along Auckland's Northern Motorway from SH1 at Silverdale to the current motorway terminus near Orewa. State Highway 1B runs from SH1 at Taupiri to Sh1 at Cambridge, providing a bypass of Hamilton.

• List of New Zealand State Highways
• List of roads and highways, for notable or famous roads worldwide