A transport commentator says NZTA's decision not to toll Transmission Gully doesn't make long-term sense.

The transport agency has decided against charging motorists to use the 27-kilometre road into Wellington when it opens next year.

It found tolling the road would divert too many drivers back to the existing coastal road.

Commentator Matt Lowrie told Mike Hosking that raises questions about the transport agency's original business case for the project.

Lowrie says road tolling needs to be considered more, as other forms of road revenue start to dry up.

"As people start switching from diesel and petrol cars, our fuel taxes will need to start changing to keep up."

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