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, 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 a new piece of road in 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, and passes through Wellsford and Warkworth, again heading for the east coast.
Just north of Warkworth, the road widens to a four-lane motorway known as Ara Tuhono, Puhoi to Warkworth motorway. In the Moir Hill section, the road widens to 6 lanes with the addition of crawler lanes on the uphill sections.
Near Puhoi, on the Hibiscus Coast, SH 1 becomes the Auckland Northern Motorway. This section of the motorway is an automated toll road. At Orewa, the motorway becomes toll-free, crossing farmland to the North Shore of Auckland. The road crosses through suburbs to the Waitematā Harbour, which it briefly follows before crossing it by the Auckland Harbour Bridge. The motorway comes off the bridge into Auckland's city centre, and forms its western boundary as SH 1 proceeds to the Central Motorway Junction.
At this junction, SH 1 becomes the Auckland Southern Motorway, and, after sweeping around the southern end of central Auckland, proceeds in a south-easterly direction. The motorway continues in a broadly southeast direction across the Auckland isthmus, then 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.