The New Zealand Transport Agency (NZTA) has unveiled design improvements for the Kapiti Expressway, adding an additional NZ$115m ($94m) to the cost of the project.

NZTA released updated cost estimates for both the MacKays to Peka Peka and Peka Peka to Otaki sections of the road.

The NZTA’s Wellington State Highway Manager Rod James said several significant changes had been made to earlier proposals in response to community feedback, as well as the outcome of further investigations and design work.

"We’ve listened closely to the community, and we’ve incorporated a number of design improvements after considering public feedback. We think this will be a good investment in the long-run by ensuring the project will work better for the local community," he said.

Under the revised estimate, the cost of McKays to Peka Peka section has risen from $550m to $630m, while the Peka Peka to Otaki project has increased from $215m to $250m.

The MacKays to Peka Peka Expressway runs for 17.8km, from north of MacKays Crossing to Peka Peka Road.

The four-lane road passes through Raumati, Paraparaumu and Waikanae, between the existing state highway and the coast and includes a new crossing of the Waikanae River. The preferred route broadly follows the Western Link Road designation, which it departs from at the southern end and north of the Waikanae River.

The Peka Peka to Otaki route runs for 13km from Peka Peka Road north of Waikanae to Taylors Road, north of Otaki. From Peka Peka Road, the expressway will follow the current state highway on the western side of the railway line, which it will cross over bridge north of Sutton Road. The expressway will then run along the eastern side of the railway line.

The four-lane expressway is expected to enhance road safety in the Kapiti due to the separation of local and highway traffic, while a bridge over the expressway at Te Horo Beach Road and at Otaki Gorge Road will link eastern and western Te Horo.

The agency said the new estimate for the Peka Peka to Otaki section now includes the cost of an additional road bridge at Rahui Road to maintain connection with central Otaki. Proposed access from the expressway for this town includes providing ramps at its north and south to ease traffic flow.

The estimated total cost of the Kapiti Expressway is expected to be NZ$2.4bn ($1.9bn).