A second harbour crossing across the Waitematā Harbour could be brought forward if National makes it into government.

A business case for the project is being prepared at the moment, but any project won't get underway before 2030.

Now National’s Leader Simon Bridges has pushed the door open, saying he might look at bringing the project forward.

Transport blogger Matt Lowrie told Heather du Plessis-Allan the biggest problem with the discussion around this second crossing is that it could make the situation worse. 

"The estimates are between $6-10 billion and you have to ask where that travel goes once we've built that, as it will have to feed into the existing motorway network."

He says that the crossing is not the problem, its the motorways on either side of the bridge. Lowrie says that without sorting out that problem, it would just lead to more congestion. 

The best outcome, he says, would be a second crossing dedicated for public transport.

"As soon as you put more cars on there, whether you toll it or not, it would actually make congestion worse for Auckland." 

Building a new road-focused bridge would see people change their habits, Lowrie argues. He says that in Houston, they spent billions to increase a highway to 28 lanes and it is more congested than ever.