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Whirokino Trestle and Manawatū River Bridge

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Project introduction

Waka Kotahi NZ Transport Agency is designing the replacement of the Whirokino Trestle, and the Manawatū River Bridge.

  • Estimated project cost

    $70 million
  • Project type

    Bridge replacement
  • Project status



The primary purpose of the project is to improve safety, efficiency and resilience. Neither Whirokino Trestle nor Manawatū River bridges currently allow high productivity motor vehicle (HPMV) loads and Whirokino Trestle is approaching the end of its structural and economic life.




This project will deliver a number of benefits, including:

  • the Whirokino Trestle and Manawatū River Bridge will be able to carry HPMV loads, meaning HPMV vehicles will no longer have to take 14km detour routes
  • improved route security with stronger bridges
  • safer bridges, with wider traffic lanes and shoulders
  • improved walking and cycling facilities
  • reduced maintenance costs
  • reduced delays as result of closures for overweight/width vehicles, and from maintenance and minor repairs.

Why this work is important

The Whirokino Trestle is reaching the end of its life and doesn’t meet current standards. It’s due to be replaced within the next 10–20 years. The Manawatū River Bridge is also below current standards. This leads to some larger freight trucks having to take a longer route to get to and from Wellington.

The replacement structures will be built on the western (coastal) side of the existing bridges, and will include wider lanes and safer road edges. The existing Ken Everett Cycleway will remain in place, to ensure a safe crossing for cyclists and other non-motorised users. These users will still need to cross the new Manawatū River Bridge – however, the wider shoulders will ensure a much safer crossing.

Replacing the Whirokino Trestle and strengthening or replacing the Manawatū River Bridge will bring them up to modern safety standards and make travel for freight vehicles more efficient.


  • What does this project involve?

    This project involves replacing the Whirokino Trestle with a new bridge over the Moutoa Floodway between the existing floodway stopbanks, a new bridge over the Manawatū River, a large earth embankment to connect the two, and tie-in of the new alignment to the existing State Highway 1 at either end. We’ll also upgrade the intersection between the bridges, where Whirokino Road and Matakarapa Road meet State Highway 1.

  • Will the new structures have a cycleway attached?

    On the new structures, there is a 1.5m wide shoulder which cyclists will use. The Ken Everett Cycleway (the pathway within the floodway) will remain open for cyclist and pedestrian use. However when this is in flood, cyclists will also be able to use the 1.5m shoulder along the Trestle.

  • What happens to the current bridges once the new ones are open to traffic?

    Demolition of the existing structures will occur after the new bridges have been completed and are open to traffic.

    See below.

    What’s happening with the old Manawatū River Bridge?

    Following ongoing interest regarding the future of the State Highway 1 old Manawatū River Bridge, Waka Kotahi NZ Transport Agency paused the planned deconstruction of the bridge in order to review the possibility of keeping the bridge.

    We are now working with technical specialists, Horizons Regional Council, Horowhenua District Council, our iwi partners and stakeholders to understand the potential impacts of keeping the old Manawatū River Bridge for use by pedestrians and bicyclists. 

    One important requirement is an amendment to the Resource Consent for the Whirokino Trestle and Manawatū River Bridge project. Our work to understand potential benefits and risks if the old bridge is kept will be part of our consent variation application.

    Further work on the old Manawatū River Bridge will depend on the outcome of the application.

  • What landscaping will be carried out?

    A new wetland will be created to the west of the new SH1 alignment, with an additional 0.97 ha of riparian planting along the Manawatū River.

    A new rest area on the south-eastern side of SH1 (approaching the Manawatū River Bridge) will also be constructed as part of the works.

  • Have there been any finds of significance?

    In early June 2018, koiwi (human remains) were found south of the project site on farmland, while stripping topsoil in preparation for earthworks. The koiwi was left in place and re-buried, after consultation with local Iwi. There have been no other finds of this nature on the project to date.

  • What are the community benefits?
    • No more 14km detours for High Productivity Motor Vehicles (i.e. HPMV – larger than the standard 44 tonne vehicles) which will be able to use the new structures.
    • Safer and stronger bridges, with wider traffic lanes and shoulders.
    • Reduced maintenance costs.
    • Fewer delays from closures for overweight/width vehicles, and from maintenance and minor repairs.
  • What are the Journey Time Savings?

    The Journey Time Savings to affected High Productivity Motor Vehicles (i.e. HPMV – larger than the standard 44 tonne vehicles) are considerable. Not having to use the 14km detour will result in savings of approximately 20 minutes per journey. Journey Time Savings for all other road users are approximately 15 seconds per vehicle, as a result of the increase in average speed due to improved road width and alignment.

  • Was consideration given to building a four-lane bridge?

    Any project the Transport Agency builds needs to be justified in terms of how much it will cost, and how many people will benefit once it is completed. This project took into account the current two-lane road between Levin and Foxton, existing traffic volumes, and how those traffic volumes are likely to change in future. Based on this information, we couldn’t justify the cost of building a wider bridge at this point in time. Using existing traffic volumes, a four-lane bridge won’t be required for approximately 25–30 years, at which point consideration could be given to a second two-lane bridge, to carry opposing traffic.