[3] 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.

[needs update] 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.

[4] 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[5] 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.

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.

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 220 km (140 mi).

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.

SH 1 enters the Manawatū-Whanganui Region, and descends through an army training area to the end of the Desert Road at Waiouru.

The highway crosses into the Wellington Region 15 km (9 mi) 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.

At Ngauranga, SH 1 becomes the Wellington Urban Motorway, skirting the shore of the harbour then passing the city centre to the west.

After passing Kaikōura, it veers inland, twisting through the Hundalee Ranges before emerging at the northern end of the Canterbury Plains.

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.

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.

SH 1 continues through gentle hill country and along the shore of Lake Waihola, then crosses the Tokomairiro Plains into Milton.

From Balclutha, the highway turns west, veering briefly north as it heads inland to avoid the rough hills of The Catlins.

In central Invercargill it meets the southern end of SH 6 and turns due south, skirting the estuary of the New River and Bluff Harbour.

A commemorative signpost at Stirling Point indicates distances to major world centres and to the start of the highway at Picton.

The sections between Wellsford and Wairakei, between Ōhau and Wellington Airport, and between Woodend and Rolleston are classified as high volume roads.

The shingle fan fords are near Kaikōura, and while generally being dry, on about 28 days a year state highway traffic used to detour around them due to high water levels on old single-lane bridges, leading to delays on a major freight route.

In 2009, the Northern Motorway was extended to Puhoi, bypassing Hibiscus Coast Highway through Orewa which was re-designated part of SH 17.

[19] The Waikato Expressway north of Te Kauwhata has largely been built on the existing line of SH 1N, although at Pōkeno the highway was diverted to bypass the town to the east.

The construction of the Ngauranga Interchange flyovers in 1984 allowed SH 1 to be diverted onto the motorway, bypassing central Wellington streets.

[34] The section from the Queen Elizabeth II Drive to Brougham Street is now a local road, while the remainder of the route forms parts of SH 74 and 76.

In the southern South Island, several particularly twisting sections of SH 1S have been rebuilt to remove sharp bends and to generally improve road conditions.

The section of Marsden Point to Whangārei will be upgraded to a four lane expressway as part of the Roads of National Significance programme.

[51] As of October 2017, the NZTA is investigating extending the Waikato Expressway south of Cambridge 16 km (9.9 mi) to the SH 1/SH 29 intersection at Piarere, bypassing the existing highway around the shores of Lake Karapiro.

[53][54] In December 2018, the NZTA selected the road's preferred corridor, bypassing Levin to the east alongside part of SH 57.