Transport officials are warning of longer travel times and heavy traffic on upper South Island roads this summer after the main route was closed by landslips. 

The New Zealand Transport Agency (NZTA) said today that the closure of State Highway One near Kaikoura has created new traffic and safety concerns on the alternative route, via the Lewis Pass and Murchison.

Speaking at a press conference at Parliament, NZTA regional performance manager Mark Owens said the Lewis Pass route would have to be upgraded to cope with the rise in traffic.

"The reality is, this will be the main highway connection for this part of the country for some time."

Owens warned motorists it was was a longer, more challenging road, which was "windy in places", and included several one-lane bridges. Drivers were urged to plan ahead and leave plenty of time for their journeys.

Motorists driving between Picton and Christchurch should now expect the journey to take at least 7.5 hours - around two hours longer than the coastal route.

Owens said the sudden upsurge in traffic on the route, especially trucks, has upset residents and created new safety concerns.

As a result, new speed restrictions have been introduced and the police presence has increased on the alternative route.

Speaking about SH1, Owens said clearing the main route was a "huge job" and would take "at least several months".

Some of the smaller slips on the highway were already being cleared. But ongoing aftershocks meant it was still too dangerous to assess the larger slips, the scale and complexity of which were "unprecedented" in New Zealand.

Each of the seven landslips on SH1 were as large as one in Manawatu Gorge in 2010, which cost $35 million to clear up.

The inland route to Kaikoura was expected to be re-opened in the next few days.

Its closure has angered some local farmers, who believe it is safe and they are being blocked from using it unfairly.

Owens said the road was still "a high risk worksite", and allowing public access would delay its re-opening.

NZ Herald