The Automobile Association says flaws in the roading network in Wellington have been exposed by a major traffic snarl-up.
Traffic was backed up on State Highway 1 for about 10km after a truck spilled oil onto the road at Ngauranga Gorge just north of the city on Monday afternoon.
The Transport Agency says a truck lost its sump heading up the Ngauranga Gorge about 2.30pm.
Traffic on the motorway was backed up for hours as far as the Basin Reserve.
The AA says the incident shows how vulnerable Wellington is.