SH58 Safety Improvements Stage 1 is a finalist in the Excellence in Road Safety Category at the 2022 IPWEA NZ Asset Management Excellence Awards.
The SH58 Safety Upgrade Improvements Stage 1 commenced designed in 2017 with construction occurring between October 2019 and November 2021. Located in Wellington and spanning from the intersection with SH2 (Haywards Hill) for a distance of 2.7km west.
The project exemplifies asset management excellence as it combines the road safety outcome desired alongside significant enhancements to route resilience and asset condition and lifecycle. The adopted solution targeted immediate reduction in high severity crashes whilst future proofing the asset against significant anticipated changes in route usage following the opening of Transmission Gully.
Asset Management Principles
The works were completed within the context of the State Highway Asset Management Plan process, applicable at the time. The Plan showed, at a strategic level, how projects were planned to deliver future needs and linked state highway investment with a customer focus and defined service targets.
The Plan linked investment decisions to Waka Kotahi’s high-level statutory and strategic objectives (e.g. Safer Journeys) and project delivery on the State Highway Network. Safer Journeys was a major component within this planning framework and targeted reductions in deaths and serious injury numbers. This structure is aligned with the principals included within the IIMM.
Given that SH58 was identified as one of the poorest performing State Highway routes from a road safety perspective (ranked 2nd worst at time of pre-implementation), the customer focused values of safe systems, safe roads and safe speeds were directly applicable to the SH58 safety improvements and formed part of a targeted 10 year programme of works to improve safety.
At a project level, asset management principals influenced many project decisions which aimed to achieve improved asset management outcomes through the delivery of this road safety upgrade. For example, the future use of the route was anticipated to change significantly following the opening of Transmission Gully with additional vehicle movements anticipated due to the improved connections that would be facilitated by SH58 in linking SH2 and Transmission Gully. An increase in traffic from 15,000 to 20,000 vehicles per day was anticipated with significantly more heavy vehicle movements now likely due to traffic no longer needing to navigate tight bends at the SH1 end of the route (which cannot currently accommodate heavy vehicle tracking). Whilst this anticipated change in traffic volumes had further and compounding implications for the road safety performance of this route, it also brought asset management challenges.
To manage this risk the project included the provision of deep lift asphalt along the entirety of Stage 1 which would offset the impacts of this increased vehicle usage along the route. This approach combatted both the loading implications of the heavy vehicles but also the stresses associated to uphill climbing and downhill braking along the route inclines and declines.
Furthermore, The replacement of a large and deep cross-road culvert, identified as being in poor condition during investigation works, was also completed which removed the risk of future failure of the pipe and addressed route flooding risks which had previously contributed to lane restrictions along the route. Similarly, the early upgrade and diversion of utilities ensured that the integrity of the new pavement asset would be protected by offsetting future replacement risks and asset conflicts.
The project also included route resilience enhancements through the provision of retaining structures and extensive slope batter works to adjacent land, including cuts of up to 35m in height. These works were combined with the implementation of catch nets and structures and will reduce landslip and rockfall vulnerability of the route associated to seismic risks present here. There will be direct benefits to users of SH58 by reducing potential for road closures along the route whilst also increasing the resilience of the wider state highway network by ensuring this route, being the alternative route to SH1/SH2, remains open to accommodate diverted vehicles in the event of closure on those key routes into Wellington.