An artist impression of the Rahui Rd overbridge, which has been proposed as part of the Peka Peka to Otaki expressway.

Construction of the final 13 kilometres of the Kapiti expressway has been given the green light, but it will cost the taxpayer $80 million more than previously thought.

Transport Minister Simon Bridges revealed on Tuesday that Fletcher Construction had won the contract to build the Peka Peka to Otaki section of the Kapiti expressway, north of Wellington, with work on the ground starting in mid-2017.

SUPPLIED Construction of the four-lane Peka Peka to Otaki expressway, north of Wellington, will begin in mid-2017 after the Government awarded the contract to Fletcher.

It is expected to be open to traffic by 2020.

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The New Zealand Transport Agency had previously estimated the project would cost $250m. On Tuesday, both Bridges and the agency said it would cost $330m.

SUPPLIED An artist impression of the new bridge over the Otaki River, which will form part of the Peka Peka to Otaki expressway.

Neil Walker, the agency's Wellington highways manager, said the $250m figure was based on the estimate for the construction phase only. The $330m estimate includes the investigation, design and property costs.

Fletcher would now start detailed design, environmental planning and other works for the project," Walker said.

"This will include further community consultation."

MARK COOTE Traffic gets a run over the new Peka Peka overbridge, which has been built as part of the Mackays Crossing to Peka Peka section of the Kapiti expressway.

Bridges said the high standard expressway would result in more reliable, safer and efficient travel to and from Wellington through the Kapiti Coast, and would continue to support economic development in the area.

It was also expected to create up to 500 jobs across the Wellington region.

The Peka Peka to Otaki expressway will eventually connect to the southern section of the expressway - a $630m, four-lane link from Mackays Crossing to Peka Peka - which is currently under construction and expected to be finished by early 2017 at the latest.

ROSS GIBLIN/FAIRFAX NZ Work continues on the Peka Peka bridge over the Kapiti expressway.

Otaki MP Nathan Guy said the expressway would bypass Otaki's township and "help remove one of the worst traffic choke-points in the lower North Island".

The town was a popular destination in its own right and this would continue, he said.

"Less heavy traffic on the streets will be welcomed by many locals."

Kapiti Mayor K Gurunathan said the Peka Peka to Otaki expressway would deliver significant benefits to the area

"Reduced travel times and our improved resilience will help unlock the Kapiti Coast's economic potential," he said.

"It will bring more wealth into our district, enabling the council to invest in services and infrastructure that will benefit all our residents."

WILL OTAKI FALL OFF THE MAP?

Cafe Te Horo owner Jackie Wood said she felt positive about the news of progress on the expressway.

The cafe was currently on SH1, about halfway between Otaki and Peka Peka. Once the expressway was complete, drivers would have to get off the expressway at Peka Peka or Otaki to reach her cafe at Hyde Park.

But if Otaki had the right shops to make it a destination then its shopping economy would survive, she said.

"Look at Taupo, I think people were worried there, maybe for the first year it might make a little bit of a difference."

Otaki ward councillor James Cootes said the local community board had worked hard with the transport agency to achieve the best result for the community.

"We all want to look back at the end of this project and be proud of what has been done," he said.

"The expressway/bypass will relieve the traffic congestion experienced by many and help cement Otaki as the destination it has become. It's exciting times ahead."