"Variable speeds are increasingly being used to match speed limits with the conditions and provide the right balance between safety and keeping traffic flowing smoothly.''
Speed limits inside the tunnel will remain at 80km/h to manage the higher risks associated with an enclosed tunnel environment.
Gliddon said authorities had been monitoring the operational and safety performance on the state highways around the tunnel since it opened.
They had also taken on customer and stakeholder feedback in the past few months.
Earlier this month, thousands of people signed a petition via the Change.Org website calling on transport authorities to increase the speed limit from 80km/h to 100km/h on Auckland's Northwestern Motorway.
The petition was started by Hamilton man Bradley Scales.
"Why, when you have a brand new four-lane wide motorway, would you make the speed limit 80km/h? To improve safety? That is the most ridiculous explanation I have heard,'' he wrote.
Police have yet to reveal the number of speed tickets they have issued since the tunnel opened.
There are speed cameras inside as well as areas around it.