The New Zealand Transport Agency (NZTA) provides a great online resource to help you plan your trip and get up-to-date information on the traffic conditions at both a national and regional level - including live updates, regional maps and webcams.
View a list of major road closures, road works and any other activity that may affect your travel plans, as well as a report of the current traffic conditions and congestion in the major cities of Auckland, Wellington & Christchurch.
It also includes detailed information about the condition of State Highway 1 between Picton and Christchurch, following extensive damage to the road caused by the November 2016 earthquake. Along with a road status report, the page outlines timings for when the highway is planned to re-open as well as alternative routes for travelling in the top half of the South Island.
Be sure to check out the Traffic and Travel information page before you start your journey.