The long-awaited Transmission Gully motorway has officially opened.

The $1.25 billion project, which has seen numerous delays, was originally due to open in April 2020.

The 27km motorway between Wellington and Kāpiti can carry 25,000 vehicles a day and is expected to shorten peak journeys by 7-15 minutes.

The road represents the largest Government investment in New Zealand’s infrastructure in a generation.

Prime Minister Jacinta Ardern officially opened the motorway in a ribbon cutting ceremony this week.

“Transmission Gully will transform the Wellington region, making it quicker and safer for people and goods to travel through the lower North Island,” she said.

“It is an example of modern infrastructure that features the highest safety measures, treads lightly through the environment and is future-proofed for generations to come.”

Infrastructure Minister Grant Robertson said Transmission Gully provides a safer and more reliable route to ensure Wellington remains connected in the event of an earthquake or major storm severing other transport routes.

“The new motorway will also have economic benefits with faster movement of freight and more resilience in our transport links,” he said.

There are four new interchanges connecting to communities along the route, with 25 major structures including bridges and large culverts constructed. 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.

Transport Minister Michael Wood said Transmission Gully is one of the most significant and complex new roading projects ever undertaken in New Zealand.

“The road spans 27 kilometres of very challenging terrain, requiring innovative environmental and construction techniques.

“Transmission Gully is built to the highest safety specifications and will provide a much safer route for road users. The new motorway will also see fewer vehicles using the old coastal route.”

Waka Kotahi said as with the opening of most major new roads, some disruption and congestion at entry and exit points can be expected as motorists adjust to new road layouts and travel patterns change.

“It could take a few months for journey times to settle, as people experiment with different routes and become familiar with the new motorway, particularly in the morning for people heading into Porirua and Wellington. We’re asking people to be patient as these new journey patterns settle,” said Waka Kotahi general manager transport services Brett Gliddon.

Gliddon said a significant amount of work remains to complete all aspects of the project, and people using the motorway will see work continuing on and around the motorway for some time.

“Over the next 12 months the contractor will be completing parts of the project that were planned for after the opening of the new road,” he said.

This includes finishing construction of the new section of SH59 between Paekākāriki and Mackays Crossing, completing the project’s walking and cycling tracks and other off-road works, and completing work on the SH58 interchange. The southern section of SH59, between Mungavin Avenue and the SH1 Transmission Gully connection at Linden, will also be repaired and resurfaced.”