GPS navigation units are directing people around Woodville, contributing to retail decline say retailers.

State Highway 3 through the Manawatu Gorge closed in April and while road signs detour people through the town, Woodville Mart owner Kevin Ashwell said GPS navigation devices were advising motorists to take an alternative route that avoided the town.

"If you go down Saddle Rd probably about eight out of 10 cars will go round the back way.

Read more: Businesses discuss Manawatu Gorge issues
Manawatu Gorge remains closed


"The GPSs in modern cars tell you, the road's closed and this is the shortest route. Travellers don't know which way to go and miss the town."

He said all Woodville businesses relied on the travelling public and any locals that were now shopping local, because of the 10-minute extra travel time to Palmerston North, were having a minimal effect.

"If anyone in Woodville had to rely on the locals we'd be closed. I wouldn't be in town if it wasn't because of the travelling public - I've been there 34 years."

Tararua Mayor Tracey Collis said the recommended route varied, depending on factors such as roadworks as well as devices used.

Automobile Association spokesman Liam Baldwin said many navigation devices could be set to a travel-time or distance preference "then algorithms sort out the route".

He said there were two main navigation data services, Tom Tom and Google Maps.

A Hawke's Bay Today Google Maps route search from Hastings to Palmerston North identified a route through the centre of Woodville and via Pahiatua Track. Another route search to Feilding took the Saddle Rd and also went through the centre of Woodville.

Mr Ashwell estimated trade was down 30 per cent across Woodville businesses, with many higher.

When the gorge was closed for 14 months several years ago it put businesses into survival mode, he said.

"You don't have a choice - you just have to go with the best you've got.

"Some of those roads were never designed for the size of the trucks going down them."

If or when the gorge road will reopen is uncertain, with repair crews withdrawn because of unstable mountainsides.

New Zealand Transport Agency regional transport system manager Ross I'Anson said it had no report on whether truck traffic contributed to gorge slips and had not sought such a report.

"We know that cutting away the toe of the hillside, originally to build the road and then to maintain the road, has contributed to some of the issues, however the main cause has been the geology of the material in the gorge and its reaction following wet weather."

Mr I'Anson told a public meeting in Woodville on Wednesday the agency was dedicated to solving the problem and the stretch of road was a priority.

The agency would report to residents four alternative routes by December but it would take two to three years to construct the chosen route.

Mr I'Anson said that since Saturday seven crews were upgrading Saddle Rd.