State Highway 3 (New Zealand)

State Highway 3 (SH 3) is one of New Zealand's eight national state highways. It serves the west coast of the country's North Island and forms a link between State Highway 1 and State Highway 2. Distances are measured from north to south.

For most of its length SH 3 is a two-lane single carriageway, with at-grade intersections and property accesses, both in rural and urban areas.

History
A Mokau – Awakino horse track was widened to a dray track about 1897. It was then possible for a horse and buggy to cover the 110 mi – now 162 km – from New Plymouth to Te Kūiti in 17½ hours. The first car to traverse the route from Auckland to New Plymouth seems to have been an 8 hp Cadillac in 1905, though Ōtorohanga to Te Kūiti was by train and, between Awakino and Mokau, a horse assisted on the beach.

A 1910 Te Kūiti meeting called for metalling of the road to Awakino. Mount Messenger Tunnel opened in 1916 and its single lane was enlarged about 1983. £3,000 (2016 equivalent $280,000) was provided in 1919 for the Awakino Gorge section, including the tunnel (enlarged in 2011), and it was opened in March 1923 at a total cost of about £60,000 (2016 equivalent $5.8m). Most of the route was gazetted as a government main highway in 1924, some sections were tar-sealed in 1925 and more work had been done on the road by 1936, leaving only a few mud sections. In 1937 the 6 mi between Ōhaupō and Te Awamutu was the only unsealed section north of Tokanui. By 1949 the road was sealed as far south as Te Kūiti and the reinforced concrete bridge over the Waipā at Ōtorohanga had been started. The 12 ft wide, single-lane, 11-span, 670 ft, steel, Mokau Bridge opened in October 1927 (official opening 17 December), replacing a punt. The cost was £35,000 (2016 equivalent $3.3m). It had a lifting span allowing passage of vessels up to 50 ft wide and with a 60 ft clearance at high tide. In 2001 the 1927 bridge was replaced by the current 9-span, 230 m, double lane, pre-stressed concrete bridge for $6.2m (2016 equivalent $8.5m). The new bridge doesn't allow for shipping, as the first ship to pass under the old lifting span was withdrawn three months after the bridge opened.

An 1871 account of a coach journey from New Plymouth to Wellington described the very poor road round the coast via Ōpunake to Whanganui and the much better and well used road south from there. A government subsidy of £3,000 (2016 equivalent $400,000) a year was being paid for the coach north of Whanganui.

Route
The highway leaves SH 1C at Hamilton, and initially heads south through farmland, passing through Te Awamutu. Sections of this stretch of the road are four-laned, but not divided carriageway. From Ōtorohanga it follows the valley of the Waipā River to Te Kūiti. The road then turns southwest through sparsely settled farmland, crossing several ridges before following the Awakino gorge to reach the coast, which it follows around the North Taranaki Bight. At the Tongaporutu River the highway turns inland to avoid coastal cliffs and climbs over Mount Messenger before descending via the Mimi River valley to return to the coast near Urenui. Bypassing Waitara, it reaches New Plymouth then turns inland, passing to the east of Mount Taranaki via Inglewood, Stratford and Eltham to Hāwera.

From Hāwera the highway follows the coast of the South Taranaki Bight south-eastwards to Patea and Whanganui before leaving the coast and heading to Bulls. Here, SH 1 from the north intersects with SH 3, and the two highways are concurrent for the next 6 km to Sanson where SH 1 diverges to the south. SH 3 continues its south-eastern route to Palmerston North, where it runs through the city streets and changes to a north-eastern direction near the city centre. It maintains this direction as far as Ashhurst, where it crosses the Manawatū River and intersects with SH 57. There is a gap in the SH 3 designation here due to the closure of the Manawatū Gorge route in 2017, and traffic between Ashhurst and Woodville is required to detour via nearby Saddle Road while a replacement highway on a new alignment is under construction. SH 3 resumes where the Saddle Road detour meets the former Manawatū Gorge route, but almost immediately thereafter enters Woodville and terminates at a junction with SH 2.

Both the Awakino and Manawatū gorges are prone to closure by slips and rockslides in heavy rain.

Route changes
Construction of a bypass of Bell Block, a satellite town of New Plymouth, was completed in 2010. The bypass is a four-lane, divided expressway with an interchange at Henwood Road providing access to Bell Block.

In 2016, a section of SH 3 in Taranaki was realigned replacing the "deadly" Normanby overbridge.

Future improvements
State Highway 3 will form part of the future/proposed Southern Links motorway project in the South/West of Hamilton and Tamahere.

In January 2016, funding was announced for road bypasses of the two tunnels north of New Plymouth. Construction of the Mount Messenger and Awakino Gorge tunnel bypasses was expected to begin within two years. On 24 August 2020 Te Korowai Tiahi o Te Hauauru, whose rohe the road crosses, withdrew support from the bypass roading project while in High Court. The Poutama Charitable Trust and New Plymouth locals protested against the project while court was in session, with the argument that this new route would destroy the valley's ecosystem. However, the Transport Agency responded by saying that the bypass is the least ecologically destructive and will deliver road safety.

The highway through the Manawatū Gorge between Ashhurst and Woodville in the Manawatū-Whanganui region was closed in April 2017 due to a large slip, with SH 3 traffic diverted via Saddle Road. Contractors were pulled out of clearing the slip in July 2017 due to ongoing geological movement in the hill, closing the road indefinitely. The NZTA began fast-tracking a long-term solution to bypass and replace the gorge. In March 2018, the NZTA announced a bypass would be built to the north of the gorge, but south of the Saddle Road. Known as Te Ahu a Turanga/Manawatū Tararua Highway, construction of the $620 million road began in January 2021 and is expected be completed in late 2024.

Spur sections
SH 3 has one spur, designated State Highway 3A. This 15.6 km stretch links State Highway 3 just west of Waitara to Inglewood, providing a shortcut and bypass of New Plymouth. The entire length of highway carries the name Mountain Road with the sole exception being a very short link of Rimu Street in Inglewood to rejoin SH 3.