Transmission Gully Motorway is one of the most significant new infrastructure developments in New Zealand's North Island. It is now open and Ventia's Transport team are proud to provide Operation and Maintenance (O&M) services to Wellington Gateway Partnership for the 25-year concession period of the Transmission Gully Motorway. It is the first roading Public Private Partnership (PPP) in New Zealand.  

The new 27 kilometre four-lane motorway joins the Kāpiti Expressway at Mackays Crossing in the north and the Porirua-Johnsonville Motorway at Linden in the south. Transmission Gully is a safer, more resilient, and more reliable way to travel to and from Wellington than the current coastal route. 

The project comprises a 27km four lane motorway connected to the existing roading network by four new interchanges and two new link roads. The project includes 23 new bridge structures of varying size, approx. 100 transverse culverts of varying length, 70km of open drainage swales, 90km of traffic barriers, approx. 900 traffic signs and some 600ha of planted areas for the Ventia team to maintain. All structures have been built to withstand a 1 in 2500-year earthquake. The largest structure, Te Ara a Toa is 230 metres long and 60 metres high. 

Ventia's O&M services will include asset management, proactive and preventative maintenance and inspections, corridor management and traffic control, structural maintenance and management, seismic monitoring and management, incident response, data collection and systems monitoring, and environmental management. 

There's also the environment to care for. Work undertaken by environmental and landscaping teams during construction will be continued. This means ensuring fences and environmental barriers are intact, vegetation is mowed and weeded, and predators are controlled, especially for ecologically protected areas. 

Thousands of vehicles, including hundreds of heavy vehicles, pass through coastal communities like Mana, Pukerua Bay and Plimmerton every day. The Transmission Gully motorway is intended to divert vehicle traffic away from these communities, with the number of vehicles using the existing coastal SH1 route expected to reduce significantly. This means those communities can look ahead to creating more liveable environments, with safer, more user-friendly facilities for pedestrians and cyclists. 

Transmission Gully route map
Map courtesy of the NZTA

Enhancing asset management capability 

Complementing Waka Kotahi's (NZTA's) asset management capability, Ventia's dedicated, site-based asset management team will work closely with the client to ensure assets are managed effectively and efficiently with minimal disruption for end-users.  

When managing any transport infrastructure we offer proactive, robust and reliable whole-of-life asset management services. Using industry-recognised systems, we collect and analyse asset condition data and use this to closely monitor the status of the network and identify and remediate any defects that might arise to ensure service levels are maintained. 

The Ventia team has developed an integrated information management system which will capture, integrate and deliver accurate asset management information for every asset and create an inventory that will support our client's infrastructure management strategy. 

This gives Waka Kotahi, and their stakeholders, confidence that our systems will effectively manage their assets appropriately, efficiently and with regular auditing.   

Investing in our people and embracing complexity  

Our dedicated team in Wellington has developed a series of operational documents and defined the project maintenance strategy. 

This was an intricate project that needed a broad range of experience and skills to successfully meet complex environmental challenges, such as tackling mountainous terrain, sensitive watercourses, and active and dormant fault lines.  

Vic Hensley, Ventia's General Manager New Zealand Transport and Major Projects said the motorway opening was a memorable day for everyone, including the Ventia team who are now operating the road. The Ventia team is providing incident response services and working with the Wellington Traffic Operations Centre to actively operate the network to manage any incidents and minimize the effect on traffic flow. 

"Building our team was about getting the right people for the job. Despite the small size of the team, they together offer an incredibly vast set of skills and experience across technical, commercial, legal, finance, project administration and management fields." 

Involvement right from the start 

A great deal of planning and preparation is required for any major infrastructure project, which is why it was important for Ventia to be there well in advance of service commencement - working with the PPP partners to gain a thorough understanding of the asset prior to the motorway opening in March 2022.  

With responsibility for all traffic operations during the concession period, the Ventia team has established early communications and strong working relationships with the Wellington Traffic Operations Centre, Police, Fire Emergency NZ and other service providers. 

Up for the challenge 

Whilst designed to withstand a significant natural disaster, Transmission Gully motorway is located on an active fault line in an area prone to seismic activity, presenting a significant operational challenge. 

The motorway is a key transport asset for the Wellington region providing infrastructure resilience and a catalyst for growth. 

Given the critical role that Transmission Gully will play in maintaining regional connectivity in the event of any significant seismic activity, the Ventia team will be closely monitoring seismic events and their effect on critical assets such as bridges and drainage elements. 

With so much water in the hills, the stormwater system needs to perform well. Ventia has established a water quality monitoring process. 

Focusing on environmental sustainability  

Located in an extremely sensitive natural environment, Transmission Gully presents stringent requirements for vegetation, landscaping, watercourses and ecology.  

The Transmission Gully project includes one of the largest native planting programmes undertaken in New Zealand as part of a construction contract, with more than 550 hectares of ecological mitigation areas being either retired from grazing or revegetated. 

Ventia's services include the monitoring and maintenance of this beautiful natural environment including; natural watercourse and resident fish species; and storm water to ensure that sediment, hydro-carbons and heavy metals do not exceed acceptable levels in these sensitive water courses or adjacent inlets. 


Photos are courtesy of the NZTA and photographer, Mark Tantrum

Transmission Gully aerial - December 2019