The road was closed for about two hours, causing significant delays for motorists.
Southern District Command Centre deployment co-ordinator Senior Sergeant Brian Benn, of Dunedin, said the truck and trailer crashed into a median barrier about 8.20am.
The road was busy but no other vehicle was damaged.
''There was significant traffic congestion,'' he said.
Inquiries by the police commercial vehicle investigation unit were continuing.
Police organised grit to be spread over the resulting oil spill.
A Fire Service southern communications spokesman said about 100 litres of diesel and oil was spilled on the highway.
A St John spokesman said an ambulance attended but the driver was not injured.
NZTA spokesman Graeme Hall said the motorway was one of the busiest roads in Dunedin, with 22,000 vehicles passing through each day, on average.
Traffic was initially backed up to Lookout Point, he said. Detours were in place from about 8.45am to about 10.45am, when the truck was removed.
NZTA provided webcam coverage of the motorway and traffic updates on its website to warn motorists of the delay.
Mr Hall was pleased with the way NZTA handled the situation.
Traffic flow returned to normal once the truck was removed.
