Ngā whakarākeitanga hoahoa matua – key design refinements
Find out more about the key design refinements for the Whangaparāoa Intersection and Wēiti River Crossing.
Further design refinements
The O Mahurangi Alliance is continuing to progress its detailed design for the future O Mahurangi - Penlink highway connection with Whangaparāoa Road at Stanmore Bay.
We supplemented existing traffic data as part of our detailed design work. To do this, we observed traffic counts and driver behaviour at key intersections in Stanmore Bay.
As a result, we’ve made three further refinements to the original Whangaparāoa intersection design. These alterations will improve traffic flow and safety outcomes:
- On Whangaparāoa Road, we’ve added another westbound lane after Cedar Terrace. This ensures future-proofed capacity for vehicles travelling from further up the peninsula to join O Mahurangi-Penlink.
- Motorists will only be able to make left turns in and out of Cedar Terrace once O Mahurangi-Penlink is ready. This prevents unsafe right turns at the intersection of Cedar Terrace and Whangaparāoa Road.
Many local residents have told us they avoid turning right out of Cedar Terrace. This is due to safety concerns associated with limited visibility and traffic speed. Our recent traffic count data showed less than three vehicles an hour at peak times turning right out of this intersection.
- Additional lane length on Whangaparāoa Road. This is for the future right turn lane to connect to Beverley Road, Wiriana Place and the existing Whangaparāoa Road property access lane.
Concept drawing - subject to refinement.
Previous design refinements
The Whangaparāoa Road connection design has been refined. This will increase efficiency, enhance stormwater management, and reduce disruption during construction.
The O Mahurangi – Penlink intersection will be built “offline,” to the west of Whangaparaoa Road, on Crown-owned land next to the Cedar Reserve. This means that during the majority of the construction works, people traveling can continue to use Whangaparāoa Road. The new road layout will be built alongside it.
Rather than joining Whangaparāoa Road at Beverley Road, the O Mahurangi – Penlink road will now continue further south to flow into the existing Whangaparāoa Road. This will be the section used by those travelling to or from the Gulf Harbour-end of the peninsula.
For those joining or exiting O Mahurangi – Penlink from the northern (Red Beach) end, a short new section of Whangaparāoa Road will be built. It will be built offline to the west of the current road alignment.
Wēiti River Crossing
The O Mahurangi alliance team explored many design improvements to the original reference design. The team settled on a revised design to deliver more benefits for the environment and the local community.
An extradosed bridge is a hybrid between the more traditional box girder and cable-stayed bridge designs. It will be the first of its kind built in New Zealand.
The box girder element means it can carry a range of services and utilities, such as power and water, to the Whangaparāoa Peninsula. There’s even space for a future sewer main. The cables allow for a longer bridge span than the ‘balanced cantilever’ bridge in O Mahurangi – Penlink’s reference design. This reduces the number of piers needed to support the bridge and thus reduces the impact on the river below.
The span arrangement achieved with an extradosed bridge also enables the piers to be clear of the navigable waterway. Its position is more respectful of ecological and cultural site constraints.
Key benefits of the revised bridge design
- Reducing the number of piers from three to two and removing the centre pier allows clearer views and passage through the navigation channel.
- Removes the need for a pier on the eastern bank of the Wēiti River and the northern-most pier can be moved to avoid excavation into the cliff face.
- Improved construction methodologies, including a reduction in temporary staging, helps to minimise greenhouse gas emissions.
- A lowered entrance to the crossing fits better with the landscape, enabling 235 metres to be trimmed off the overall crossing and reducing the amount of steel and concrete required.
- A reduction in the amount of concrete required significantly reduces construction emissions.
Managing the Whangaparāoa Road flood risk at Stanmore Bay
Stormwater wetlands will be created to capture and treat stormwater run-off from road surfaces. This reduces the risk of flooding in this low-lying area. Currently, flood waters overtop Whangaparāoa Road in a one in 10-year storm event. The new design will allow the intersection to continue operating during a one in 100-year event. The wetland areas will feature ponds, landscaping and pathways.