State Highway 58 Safety Improvements—Detailed Design

State Highway 58 (SH58) is one of the most dangerous roads in New Zealand (NZ). High speed and traffic volume as well as side-road hazards and poor geometry mean SH58 has one of the worst safety records. The number of high-severity crashes left the local community in a crisis point.

We helped the NZ Transport Agency respond—having won the contract for detailed design and construction monitoring, we accelerated our delivery programme and completed the design, consents, and land acquisition in nine months rather than the normal 18–24.

Our geologists undertook a major drilling programme providing insight into challenging geotechnical conditions, informing route design, and allowing us to balance constructability, value for money, and innovation with design requirements, cost, construction methods, and road user impacts.

Extending this insight and incorporating stakeholder feedback, we challenged one-size-fits-all standards and used probabilistic analysis to inform design. By investigating several complex geotechnical and geometric alternatives, we negotiated design departures—reducing costs and the extent of works while meeting key project outcomes, namely improving road user experience and mitigating visual and ecological effects through landscape design.

Our design’s critical safety improvements—enhanced geometry, median and side barriers, and intersection upgrades with new roundabouts—are designed to slow traffic and prevent high-severity crashes.