Both northbound lanes are now open again on Western Hutt Rd near Silverstream, after a car and trailer rolled.
Police attended at the accident, which happened just after 9.20am, on the motorway between the Silverstream turnoff and the bridge over the Hutt River.
Police central communications Inspector Bruce Mackay said there were no injuries from the incident, but due to the closure of one of the lanes for an hour, northbound traffic had been delayed.
He said it was not yet known what had caused the vehicle to overturn.
- The Dominion Post
The $850m Transmission Gully will be ...Related story: Ball gets rolling on Transmission Gully