Truckers faced with treacherous South Island roads are quitting and the industry is short of 2000 drivers, the head of the commercial freight organisation says.

Photo: RNZ / Tracy Neal.

Thousands more cars and trucks have been diverted through Marlborough's inland highway after last November's quake closed State Highway 1 through Kaikōura.

Since then, driving the upper South Island's alternative highway has been a dodgem of potholes, blown out tyres lying shredded on the roadside, and endless road works.

Earlier this year, truckers raised concerns about the safety of the alternative route between Picton and Christchurch.

Photo: Supplied / NZTA

The inland route via the Lewis Pass was never intended to be a main arterial route but that changed when the Kaikōura earthquake forced coastal sections of State Highway 1 to be closed.

The New Zealand Transport Agency has budgeted about $60 million for repairing and maintaining a highway that was never designed to cope with the volume of vehicles and heavy trucks, which soared from an average 400 to 2000 daily through the alpine village of St Arnaud. In Murchison the figure doubled to more than 4000 vehicles a day.

Road Transport Forum head Ken Shirley said delays and problems with the road have caused truck drivers to either refuse to use it, or quit the industry. The industry was short of about 2000 drivers.

"There's a lot of pressure on the truck drivers and some are refusing to work that route and some are just quitting at a time when we're desperately short of drivers."

He said the problem was compounded by the industry failing to attract younger people.

"It's quite significant. The industry has commissioned reports on this. The average age of a heavy motor vehicle driver is 54 - you've got a lot of retirement looming and young people are just not wanting to join our industry."

Mr Shirley said it was possible that the traditionally long hours and lack of pay increases put many off.

An Auckland trucking boss, Chris Carr, said the road conditions have created added pressures, including logistics around ensuring drivers do not exceed their maximum daily hours on the road.

"What we used to do with a truck based in Christchurch - we'd go up to Picton, return to Christchurch and then a different driver would take it back up again. Potentially we were doing two trips in one day."

Mr Carr said they were now doing one trip in two days, and the extra distance and time cut productivity by 25 per cent.

"Obviously that pushes costs up because you're accommodating people and what used to be a five-hour trip is now between eight and a half to nine-and-a-half hours. It's not possible to do a return trip in a day."

Mr Shirley said the recent re-opening of a limited rail freight service between Picton and Christchurch made only a minor difference to the number of trucks on the road. It closed again recently after heavy rain in Kaikōura brought down more slips.

A mechanic and tow truck operator in St Arnaud said he does not expect much improvement for the next couple of years. Alistair Nicholls has been operating a 24-7 roadside rescue service, and has had to expand his business since the quake to cope.

"All the trucking firms I've come across are saying they're committed to being on this road for the next two years at least. To me, that's too long for the standard of repairs that are being done," Mr Nicholls said.

Mr Shirley said December's planned re-opening of State Highway 1 through Kaikōura is expected to take about 2000 trucks a month off the inland road. He said it was likely to be a while before it was operating at optimum levels, but it would eventually be better than before the quake.

The NZ Transport Agency confirmed on Friday that plans to re-open State Highway 1 north of Kaikōura will be done in time for the Christmas travel period.