SH1 Tinwald Corridor Improvements

The SH1 Tinwald Corridor Improvements project transformed a complex section of the state highway through Tinwald by reducing severance and access issues, mitigating delay to SH1 traffic and reducing crash risks. The upgrade delivered new traffic signals, safer rail crossings and innovative solutions like the offset limit line and automatic double-gate crossing, now adopted as a national standard.

The intersection of SH1 and Lagmhor Road in Tinwald, south of Ashburton, had long been a high-risk area. Safety issues arose from heavy traffic volumes, proximity to the Main South rail line and insufficient space for large trucks to queue safely without blocking the tracks. Near-miss incidents were frequent and raised serious community and stakeholder concerns.

Waka Kotahi required a solution that would:

• Improve safety at the rail crossing and intersection
• Reduce severance for the community by enabling safer access to schools, shops and residential areas
• Meet defined cost and programme objectives while ensuring efficiency and minimising disruption to SH1 traffic

GHD led the project from the commencement of the single stage business case (SSBC) through to detailed design, consenting, procurement and construction support. We worked closely with Waka Kotahi, KiwiRail, Ashburton District Council and Fulton Hogan to achieve a best-for-project outcome.

We delivered an innovative intersection design featuring an “offset limit line” to eliminate short-stacking risks without requiring land purchase or rail relocation. A safer rail crossing was also introduced through the design of a new automatic double-gate pedestrian and cycle crossing, which has since been adopted by KiwiRail as a national standard. To minimise costs, earthworks and traffic disruption, the project incorporated the use of EME2 asphalt - a high-performance pavement material.

Stakeholder engagement was central to our approach. We hosted community open days, collaborated closely with KiwiRail and proactively engaged local businesses and schools to build trust and support. Despite site and utility challenges, the project remained on schedule and was completed three days ahead of plan.

The SH1 Tinwald Corridor Improvements project has delivered lasting benefits for the Tinwald residents and road users across Canterbury. Since completion, crashes at the intersection have dropped significantly, with only one non-injury crash recorded compared to an average of more than six per year previously.

The new signalised intersection and upgraded rail crossing have created safer connections for children walking or cycling to school and residents accessing local shops and recreational areas. Beyond improved safety, the project has left a strong legacy for the industry. The innovative offset limit line design now sets a benchmark for addressing short-stacking issues nationwide. The double automatic gate crossing, developed in partnership with KiwiRail, has been adopted as a national standard.

These positive outcomes have strengthened community trust and reinforced stakeholder confidence. NZTA awarded GHD a 95% PACE score for the business case and KiwiRail engaged us for further projects on the strength of our performance. The project has future-proofed Tinwald by reducing severance and improving accessibility, enabling safer active transport options and supporting more sustainable community growth.