Due for completion in 2028, this 6.5 kilometre tunnel beneath Sydney Harbour will create a new link between the WestConnex M4–M8 Rozelle Interchange and the Warringah Freeway at North Sydney.  Designed as twin three lane tunnels, the project will ease congestion and improve travel times between Inner West and North Sydney, strengthening economic productivity and supporting Sydney’s long-term population growth. During delivery, the project will generate up to 6,900 fulltime jobs providing significant economic stimulus.

Western Harbour Tunnel is being delivered in two stages:

• Stage 1 was completed in February 2025, and involved the excavation of 1.7 kilometres of tunnel from Rozelle to Birchgrove. This phase removed spoil equivalent to 400 Olympic-sized swimming pools, applied 53,000 cubic metres of shotcrete to the tunnel lining, recorded more than 2.36 million hours of work by the project team and approximately 49,000 hours of independent certification work, demonstrating the scale and precision required for underground construction in a dense urban environment.
• Stage 2 design commenced in January 2023, with construction beginning in May 2023. This phase extends the tunnels a further 4.8 kilometres north to Cammeray, including two 1.5 kilometre tunnels beneath Sydney Harbour being constructed using the largest tunnel boring machines (TBM) deployed in the Southern Hemisphere.

Using TBMs to tunnel under Sydney Harbour means the bulk of construction activities are underground, minimising disruptions to the community and the environment.

The Stage 2 scope includes full civil, mechanical, and electrical fit-out of both tunnels, including the installation of advanced lighting, jet fans, fire and life safety systems, communications, and traffic control technologies to ensure safe, efficient performance once open. The project also involves complex control systems interfaces with the Warringah Freeway and WestConnex at either end of the tunnel.

Ensuring excellence: Independent certification safeguarding project integrity

As the Independent Certifier (IC) for both Stage 1 and Stage 2 of the Western Harbour Tunnel, our team—working in partnership with Bureau Veritas Buildings & Infrastructure (BVBI) — have played a pivotal role in the design review and certification of this complex, multi-stage project with over 170,000 hours of independent certification work completed (as at September 2026).

This has included managing scope interfaces between stages, coordinating adjacent infrastructure stakeholders, and verifying that all design and construction work meets with the project’s safety, quality and performance requirements.

Across the stages, critical design packages were reviewed efficiently with the majority of design review completed well ahead of the standard 20-day turnaround. This accelerated approach enabled earlier commencement of works and reduced the risk of construction progressing without certified designs.

BVBI-SMEC’s IC team collaborated closely with the Client and Contractors to ensure seamless coordination between Stage 1 and Stage 2, with proactive identification and resolution of key interface risks and challenges associated with this major infrastructure connection.

Other key aspects of the project that have been supported by the team’s compliance reviews include:

• Tunnel systems: Oversight of all mechanical and electrical systems, including the Operations Management and Control System responsible for traffic management and integration with the broader WestConnex and Sydney road network.
• Contaminated work sites: Supporting alignment modifications to avoid the former Waverton tip and mitigate contamination risks.
• Traffic: Reviewing complex traffic arrangements for tie‑in with the Warringah Freeway Upgrade (WFU) to ensure consistency, safety and operational integrity.

In parallel, our team also supported Transport for NSW through technical and Safety-in-Design forums, drawing on experience from comparable major infrastructure projects to strengthen assurance outcomes and confidence.