Designing safety into a primary regional NSW corridor

Balancing community, environmental and transport needs from concept to delivery

The Princes Highway is a primary north-south route along the New South Wales South Coast. It forms a key part of the transport network servicing residential, tourism, defence and industrial areas within the Shoalhaven local government area (LGA) and provides road users access to areas including Falls Creek, Huskisson, Vincentia and other villages.

Nearby manufacturing and production industries, agriculture, aquaculture and forestry land uses, as well as retail trade, construction, and defence industries all rely on the Princes Highway for freight transport, with efficient movement required to minimise business costs.

In 2024, we were appointed as a design partner, as part of the MRB Technical Services Joint Venture (MRB JV), to support the upgrade of a 6.5km section of the Princes Highway between Jervis Bay Road intersection and about 1.5km south of Hawken Road. This section is vital for community connectivity, tourism and freight movement on the South Coast.

MRB JV – comprising Mott MacDonald, RPS Tetra Tech and BG&E – were appointed to provide concept design and environmental assessment services for this upgrade. Working closely with Transport’s project team, the JV aligned design, assessment and stakeholder inputs early to reduce the risk of change once construction began.

The concept design converts the existing two-lane undivided highway into a four-lane divided carriageway, with median barriers, wide centrelines and a proposed S-type grade-separated interchange at Hawken Road, connecting the highway with Blackbutt Range Road. The interchange upgrade will address key safety concerns while improving local access and traffic flow.

The project was delivered through a collaborative partnership between MRB and Transport, with the team co-located in a dedicated project office for an intensive six-week value engineering phase. This helped the team identify and resolve design risks early, refine the preferred design through optioneering, and align design intent with constructability and stakeholder requirements.

Designing around environment and community

Improving safety on the Princes Highway meant designing within a sensitive environmental and community setting, where national parks, threatened flora and fauna and nearby homes all influenced the preferred concept design.

Rather than treating these constraints as late-stage issues, the team embedded them into the core design process. Alignments were refined to reduce the project footprint and avoid sensitive habitats where possible, while mitigation measures were considered from the outset to support approvals, constructability and community outcomes.

At Hawken Road, optioneering helped reduce the interchange footprint and minimise impacts on surrounding ecological areas. The vertical design was also adjusted so the highway passes over the local road, reducing excavation into potential acid sulfate rock and lowering environmental risk.

Fauna movement was addressed through the incorporation of fauna underpasses in the design, and space-proofing for tree-dwelling crossings in fauna connectivity zones.

The design also responds to local access, flood resilience and future traffic movement needs. Dedicated service roads separate local residential movements from highway traffic, while adjusted drainage structures provide permanent and temporary flood management. Rehabilitation, landscaping and provision for active transport links help integrate the upgrade into its surrounding context while allowing for future corridor needs.

The JV also coordinated closely with adjacent infrastructure projects, including the Jervis Bay Road intersection upgrade, to support continuity across the corridor. Together, these decisions show how technical design, environmental stewardship and construction practicality were considered as one integrated challenge.

Before safety upgrades (image credit: Transport for New South Wales)

After safety upgrades (image credit: Transport for New South Wales)

Before safety upgrades (image credit: Transport for New South Wales)

After safety upgrades (image credit: Transport for New South Wales)

Before safety upgrades (image credit: Transport for New South Wales)

After safety upgrades (image credit: Transport for New South Wales)

Outcomes and next steps

This upgrade will provide improved safety, reliability and resilience along one of the South Coast’s most important transport corridors.

Converting the existing two-lane road into a divided carriageway will reduce the risk of collisions, improve traffic flow and provide more reliable journey times. Dedicated service roads, emergency access and U-turn facilities, and truck parking zones will also improve local access, operational resilience and corridor functionality, while supporting freight efficiency, tourism and economic activity.

Community engagement was undertaken as part of the Review of Environmental Factors (REF) process in 2026. This included public information sessions across the region. Feedback from this process will inform detailed design development and help shape subsequent stages of the programme.

Building safer, more resilient regional connections

This Princes Highway upgrade shows how integrated concept design and early collaboration can deliver safer, more resilient infrastructure at corridor scale. By aligning technical design with environmental constraints, stakeholder needs and long-term programme objectives, the project is helping set the foundation for a safer, more reliable regional transport corridor – and for future upgrades across Australia’s regional road networks.