The NZ Transport Agency has announced the Transmission Gully motorway will not be tolled.

The Transmission Gully motorway is a 27km, four-lane road designed to improve the safety and resilience of the transport network into Wellington.

"In line with our tolling policy, the Transport Agency assesses all new state highway projects for tolling feasibility," Transport Agency director of regional relationships Emma Speight said.

"Part of this feasibility assessment is to understand the impacts that tolling might have on road users, the transport system, and local communities.

"When considering whether tolling may be appropriate, we need to weigh the potential benefits netted in revenue against any likely negative impacts in terms of safety, access and value-for-money.

"Our assessment indicated the net potential revenue over the lifetime of the toll was unlikely to make a meaningful contribution to the cost of the road.

"In addition, our assessment showed tolling the road would likely result in more drivers choosing to use the coastal route (the current SH1), which would compromise the safety, environmental and access benefits which the new road will deliver for drivers as well as for communities along the coastal route.

"The Transport Agency was also asked to consider whether tolling could be used as a measure to reduce congestion in the region by managing demand.

"Modelling in this instance indicated that tolling Transmission Gully would be ineffective in encouraging people to choose other modes of transport and would more likely encourage people to take their cars on the coastal route.

"In this instance, it has been decided that Transmission Gully is not suitable for tolling."