The Tirau to Waiouru Rehabilitation Accelerated Program (TWRAP), is one of New Zealand’s most ambitious road rehabilitation projects, targeted at addressing significant pavement renewals and pothole repairs.
The work scope includes extensive road rebuilds and re-seals. The program’s objective is to restore the road to the expected service levels by providing a stronger more durable network, less prone to potholes and frequent costly maintenance interventions, which impact road users and freight operators.
To address the pressing network needs, Downer developed and presented a network asset investment strategy to the NZ Transport Agency Board. The NZ Transport Agency agreed to fund the increased investment needed for an accelerated pavement renewal program.
The accelerated program effectively compressed five years of funding (five years’ worth of planned works), into an 18-month delivery program across two construction seasons. The condensed nature of the program minimises cost escalation impacts, generating an anticipated $16.5 million in savings – a huge benefit to the customer.
TWRAP’s innovative approach has also achieved an approximate 8.5% reduction in rehabilitation construction costs, with significant savings in temporary traffic management, design, investigation and MSQA. A dedicated pavement design team undertook targeted investigations and a thorough asset condition analysis of the pavement layers. Their analysis of various pavement configurations led to a 25–year pavement design life that will offer optimal whole of life efficiencies.
Innovative traffic management approaches included the combination of work zones and block road closures to allow intensive road rebuilding and longer treatment sections to be completed within the shortest practical timeframe. 80% of the work has been completed under full road closures, leading to production efficiencies of over 40% across the longer work sections. Innovative road cone retrieval machines improved safety outcomes by reducing road worker exposure to traffic and reducing the number of required traffic management resources.
The TWRAP model’s fresh approach to State Highway maintenance and renewals is generating enhanced value and quality outcomes. This highly effective alternative to traditional approaches sets a new benchmark and is something we will continue to build on in future maintenance solutions.
