From Sydney Harbour to the South Pacific: 10 Infrastructure Projects to Watch Across Australia, New Zealand & the Pacific

From Sydney Harbour to the South Pacific: 10 Infrastructure Projects to Watch Across Australia, New Zealand & the Pacific

Forty-five metres beneath a Sydney sports ground, two machines weighing 4,350 tonnes each are driving towards the harbour.

Patyegarang and Barangaroo are 15.7 metres in diameter, making them the largest tunnel boring machines used in the Southern Hemisphere. Their task is relatively short by the standards of modern tunnelling: excavating the final 1.5 km of the twin Western Harbour Tunnel. The ground above them, however, includes Sydney Harbour and some of the most intensively developed urban land in Australia.

Across Australia, New Zealand and the Pacific, distance and geography repeatedly determine the value of infrastructure. Melbourne is boring 26 km of twin suburban railway tunnels, New Zealand is moving millions of cubic metres of earth for new highways, and Australia’s Inland Rail is constructing a new alignment around a steep and winding section of existing railway.

In Vanuatu, a 65 km road is being rebuilt to remain usable through floods, cyclones and heavy rainfall. In Papua New Guinea, dozens of bridges are being replaced or rehabilitated along the Highlands Highway. On Guadalcanal, a 71.5 metre hydropower dam is rising inland from Honiara while roads and wharves are being strengthened elsewhere on the island.

These are places where alternative routes can be hundreds of kilometres away, difficult to use or simply nonexistent.

Briefing

• Two 15.7 metre diameter TBMs are excavating beneath Sydney Harbour as construction of the 6.5 km Western Harbour Tunnel enters its final tunnelling stage.
• Melbourne’s Suburban Rail Loop East includes 26 km of twin tunnels and six new underground stations between Cheltenham and Box Hill.
• New Zealand’s 24 km Ōtaki to north of Levin expressway will require approximately 4.5 million cubic metres of earthworks.
• The 15 MW Tina River Hydropower Development Project in Solomon Islands combines a 71.5 metre dam, 3.3 km headrace tunnel and 66 kV transmission infrastructure.
• Papua New Guinea is upgrading 71 bridges along the Highlands Highway between Lae Nadzab Airport and Kagamuga Airport.

1. Western Harbour Tunnel, Australia

Sydney’s Western Harbour Tunnel is now being excavated beneath the harbour itself.

The project will provide a 6.5 km motorway connection between the Warringah Freeway at North Sydney and the WestConnex network at Rozelle. Much of the tunnel has already been excavated using roadheaders, but the final 1.5 km beneath the harbour requires two enormous slurry tunnel boring machines.

Patyegarang began tunnelling in June 2026, followed by Barangaroo in August. Each machine measures 15.7 metres across and weighs 4,350 tonnes. They were assembled underground and operate from a launch point 44.7 metres beneath Birchgrove Oval. Together they will install around 13,000 precast concrete segments and 1,300 culverts weighing 20 tonnes each.

The machines are supported by an underground slurry treatment plant capable of pumping up to three million litres of slurry per hour to each TBM face. Maintaining face pressure is particularly important beneath the harbour, where the machines encounter soft marine sediments rather than the sandstone excavated elsewhere on the route.

The tunnel is scheduled to open to traffic in 2028.

2. Sydney Metro West, Australia

Sydney Metro West completed its main tunnelling programme in March 2026, but construction of the railway is far from finished.

The new underground railway will run between Westmead and the Sydney CBD, with stations at Westmead, Parramatta, Sydney Olympic Park, North Strathfield, Burwood North, Five Dock, The Bays, Pyrmont and Hunter Street.

Six TBMs excavated 24 km of twin tunnels during a 34-month programme involving more than 22,900 workers. The final machine broke through into the Hunter Street cavern on 2 March, completing the tunnelling programme.

Construction has since moved into another phase. Excavation crews remained at station sites during 2026 while contractors began preparations for station construction, track and rail systems installation and the 38 hectare stabling and maintenance facility at Clyde. Around 60 km of track will eventually be installed across the network, together with power, ventilation, communications, fire systems and other railway infrastructure.

The railway is targeting an opening in 2032.

3. Suburban Rail Loop East, Australia

Melbourne’s Suburban Rail Loop moved into active tunnelling during 2026.

SRL East is the first section of the planned orbital railway and will run between Cheltenham and Box Hill through Melbourne’s eastern and south-eastern suburbs. It comprises 26 km of twin tunnels connecting six new underground stations at Cheltenham, Clayton, Monash, Glen Waverley, Burwood and Box Hill.

The tunnels will reach approximately 60 metres below ground at their deepest point. The TBMs are more than 100 metres long, with cutterheads exceeding seven metres in diameter, and will operate using renewable electricity.

Construction is taking place across all six station locations as well as the Heatherton stabling facility. Unlike Melbourne’s existing radial railway network, which is concentrated on journeys towards and away from the central city, the new line will connect employment, education, health and retail centres across the suburbs.

Passenger services on SRL East are planned to begin in 2035.

4. Inland Rail, Australia

Away from the metropolitan tunnelling programmes, Inland Rail is altering the geometry of Australia’s interstate freight network.

Construction during 2026 has concentrated on sections south of Parkes. Major works are under way between Albury and Illabo, while construction began in mid-2026 on the new Illabo to Stockinbingal section in New South Wales.

The latter involves 39 km of new standard-gauge railway and 3 km of upgraded track. The new alignment bypasses Cootamundra and the steep, winding railway through the Bethungra Range, including the existing Bethungra Spiral. The works include two rail bridges over roads, eight waterway bridges, a road-over-rail bridge at Burley Griffin Way, ten stock underpasses, a crossing loop and level crossings.

By the beginning of October, the first section of new track had been laid at Stockinbingal and almost 75% of the required rail had been delivered to worksites. Construction was also advancing on the Burley Griffin Way overpass.

Elsewhere along the southern corridor, existing bridges, track and other structures are being modified to provide sufficient clearance for double-stacked freight trains.

5. Ōtaki to North of Levin, New Zealand

North of Wellington, construction is under way on a new 24 km four-lane State Highway 1 corridor between Ōtaki and north of Levin.

Main construction began in October 2025, with the first season dominated by earthworks, stormwater and drainage preparation, vegetation clearance, stream diversions, haul roads and foundations for structures. Completion is expected in late 2029.

Around 4.5 million cubic metres of material will be moved during the project, including approximately 750,000 cubic metres during the first construction season.

The project continues the modernisation of State Highway 1 north of Wellington beyond the already completed Peka Peka to Ōtaki expressway, extending a higher-capacity route towards Levin.

6. Takitimu North Link, New Zealand

On the North Island’s Bay of Plenty, the first stage of Takitimu North Link is creating a new 6.8 km four-lane route between Tauranga and Te Puna.

The alignment includes ten bridges totalling approximately 1.6 km, with 45 spans and around 12 km of piles. Structures range from 20 metres to 360 metres in length and between six and 25 metres in height. The works include a new crossing of the Wairoa River, an interchange at Minden Road, underpasses and connections into the existing state highway network.

Construction remained active throughout 2026 as the project moved from its major earthworks phase towards pavement and finishing works. Stage 1 is due for completion in 2028.

The route sits within one of New Zealand’s principal freight regions. Tauranga is home to the country’s largest seaport by freight volume, while the Bay of Plenty road network connects with Auckland and Hamilton farther west and north.

7. Tina River Hydropower Development Project, Solomon Islands

Inland from Honiara on Guadalcanal, construction of the Tina River Hydropower Development Project combines dam engineering, tunnelling, roads and power transmission within a single site.

The project centres on a 71.5 metre high dam on the Tina River. Water will pass through an approximately 3.3 km headrace tunnel to a powerhouse containing three 5 MW generating units. Dual 66 kV transmission lines will connect the scheme towards the existing Lungga Power Station, while approximately 21.5 km of permanent and temporary access roads serve the dam, powerhouse, tunnel portals, quarries and other works.

By 10 May 2026, overall construction progress had reached 30.6%. The roller-compacted concrete cofferdam had reached its design elevation, excavation of the surge tower had been completed to a depth of 31.82 metres, and structural work was progressing at the powerhouse.

Preparations were also advancing for the tunnel boring machine, including mould fabrication and production of lining segments. Geotechnical work continued around the dam’s right abutment, where consultants were analysing borehole data as the construction programme was revised.

8. South Santo Road, Vanuatu

On Espiritu Santo, the scale is smaller but the engineering conditions are severe.

The Vanuatu Climate Resilient Transport Project is upgrading 65 km of South Santo Road, a route serving more than 40,000 people. The US$142.8 million programme is expected to be completed in December 2026.

The works include pavement using locally sourced aggregates, strengthened or replacement bridges, enlarged culverts and coastal protection. Wet crossings are intended to keep sections usable during floods, while the overall design responds to heavy rainfall, landslides, cyclones and coastal exposure.

For communities along the route, prolonged closure can interrupt access to schools, health facilities and markets. The road therefore has to perform as a continuous system, with bridges, drainage, pavement and coastal structures designed around the same exposure to extreme weather.

9. Land and Maritime Connectivity Project, Solomon Islands

Road and maritime infrastructure are being upgraded together on Guadalcanal.

The second tranche of the Land and Maritime Connectivity Project is rehabilitating or upgrading approximately 35 km of urban and rural roads in Honiara and surrounding parts of Guadalcanal Province. It also includes two rural wharves and reconstruction and strengthening of an older wharf at Honiara port.

ADB reported civil works as ongoing during 2026, with completion of those works expected during the year. By late July, around US$25.27 million of the US$28 million grant had been committed through contract awards.

The combination reflects the transport geography of an archipelago. A road improvement that ends at the coast and a maritime facility without reliable land access solve only part of the journey.

10. Highlands Highway Bridge Programme, Papua New Guinea

The Highlands Highway connects Papua New Guinea’s interior with the coast and the port of Lae.

The second tranche of the Sustainable Highlands Highway Investment Program is upgrading 71 bridges between Lae Nadzab Airport and Kagamuga Airport at Mount Hagen to current design standards and to improve their resilience to climate risks.

Construction is divided across three main civil works packages. One covers 35 bridges, another 19 and the third 17. The programme combines rehabilitation of existing structures with complete bridge replacement and the construction of temporary detour bridges needed to maintain traffic while permanent structures are built.

ADB’s latest implementation data put the three packages at approximately 83%, 78% and 75% physical completion respectively, with replacement bridges still at different stages of construction.

The programme is also building a bridge asset management system covering the national network. Inspections and data analysis had been completed for hundreds of structures, bringing condition information into the maintenance system alongside the physical construction programme.

In mountainous terrain where the highway connects communities, agricultural production and mineral regions with the coast, an individual bridge can determine whether hundreds of kilometres of road function as a corridor at all.

Infrastructure Across Distance

Australia’s projects demonstrate the engineering scale available to large metropolitan and freight programmes: enormous TBMs beneath Sydney Harbour, 26 km of twin railway tunnels beneath Melbourne and new freight alignments through regional New South Wales. In New Zealand, millions of cubic metres of earthworks and kilometres of piling are being used to create comparatively short highway corridors through difficult terrain and established communities.

Across the Pacific islands, redundancy becomes harder to provide. South Santo Road, the Highlands Highway and Guadalcanal’s roads and wharves cannot always divert traffic onto another motorway, railway or nearby port when a bridge fails or a cyclone closes a route. Tina River similarly has to combine generation, tunnelling, transmission and access infrastructure because each element depends on the others.

The distances between these ten projects are enormous. Their engineering is connected by a common constraint: whether beneath a harbour, across a mountain range or along the coast of an island, the route has to keep working when there may be few practical alternatives.

Key Industry Questions

1. What is the Western Harbour Tunnel? It is a 6.5 km motorway tunnel beneath Sydney Harbour connecting the Warringah Freeway at North Sydney with WestConnex at Rozelle. It is scheduled to open in 2028.
2. How large are the TBMs being used beneath Sydney Harbour? Patyegarang and Barangaroo are each 15.7 metres in diameter and weigh approximately 4,350 tonnes, making them the largest TBMs used in the Southern Hemisphere.
3. How much tunnelling was required for Sydney Metro West? Six TBMs excavated 24 km of twin tunnels between Westmead and the Sydney CBD during a 34-month tunnelling programme completed in March 2026.
4. What is being built for Melbourne’s Suburban Rail Loop East? The first stage includes 26 km of twin tunnels and six underground stations between Cheltenham and Box Hill.
5. What is under construction on Inland Rail in 2026? Major works include upgrades between Albury and Illabo and construction of 39 km of new railway between Illabo and Stockinbingal in New South Wales.
6. How much material will be moved for the Ōtaki to north of Levin highway? The project is expected to involve approximately 4.5 million cubic metres of earthworks across its 24 km alignment.
7. How large is the Tina River Hydropower Project? The scheme has 15 MW of generating capacity, with a 71.5 metre dam and approximately 3.3 km headrace tunnel.
8. What is being upgraded on South Santo Road in Vanuatu? Approximately 65 km of road is being improved with stronger bridges, larger culverts, pavement, coastal protection and flood-resilient crossings.
9. Why does the Solomon Islands connectivity project include both roads and wharves? Inter-island maritime transport and local road networks operate as parts of the same transport system, so reliable connections depend on infrastructure at both ends of the journey.
10. How many bridges are being upgraded on Papua New Guinea’s Highlands Highway? The second tranche of the Sustainable Highlands Highway Investment Program covers 71 bridges between Lae Nadzab Airport and Kagamuga Airport at Mount Hagen.

Strategic Takeaways

1. Australia’s current transport programme is deploying some of the world’s largest tunnelling equipment across simultaneous underground projects in Sydney and Melbourne.
2. New Zealand’s current highway construction shows how relatively short new corridors can require substantial earthworks and structural engineering where terrain and existing development constrain alignments.
3. Climate resilience in Pacific infrastructure is often a basic design requirement, particularly for bridges, drainage, coastal roads and maritime facilities.
4. Road and maritime investment cannot always be separated across island states, where the reliability of a journey depends on both the land connection and the port or wharf at its end.
5. Limited network redundancy changes infrastructure economics: the operational value of an individual bridge, road section, wharf or power connection can extend far beyond its physical size.

Explore the Global Infrastructure Series

This article is part of Highways.Today’s global review of 110 infrastructure projects across 11 regions, examining the major transport, energy and civil engineering projects shaping investment and construction around the world.

• Middle East & North Africa
• Southeast Asia
• Africa
• Latin America
• Europe
• North America
• Central Asia
• South Asia
• China
• East Asia
• Australia, New Zealand & the Pacific