Transport Minister Simon Bridges has today opened the upgrade to the Causeway on Auckland's Northwestern Motorway, marking another milestone in completing the Western Ring Route.

The Causeway Upgrade Project has widened and raised a 4.8km section of the Northwestern Motorway between Te Atatu and Great North Road.

"This upgrade creates extra capacity for motorists heading to and from the growing western areas of Auckland, and links with the Waterview Connection to connect the city's motorways," Mr Bridges says.

"Both projects are part of the Government's $2.4 billion Western Ring Route project which creates an efficient additional route to State Highway 1.

"Adding extra traffic lanes as well as a bus shoulder lane in both directions and improvements to the cycleway, will make journey times on the Northwestern Motorway more predictable. It will also ensure it's able to handle the growing demands of everyone who uses it – drivers, bus users and those who walk and cycle.

"By raising the road level by at least a metre and a half the Causeway Upgrade also prevents flooding on the lanes from the nearby marine reserve and creates a safer and more reliable route for all road users."