Three deaths in as many months and 209 crashes in six years has prompted calls for urgent safety changes to a notorious South Island highway.

The dangers of State Highway 6 between Queenstown and Five Rivers were highlighted only weeks ago when on November 1 two 23-year-old Americans were killed when their rental car passed a truck on a yellow line and hit a bus. Eight people on the bus were injured.

The stretch of highway becomes congested with tourist buses, rental cars, Queenstown commuters, Southland contractors and locals. Traffic increases during summer, going from about 1800 daily trips in June/July to about 3500 in January.

Supplied A car passes a truck and trailer in the "dips" on SH6, just south of Kingston.

Part of the highway winds around Lake Wakatipu and is so narrow and windy it is known as the Devil's Staircase. The southern half, which cuts through farmland, is straight but large dips stop drivers from seeing oncoming traffic.

One truck driver who drove the road daily said cars crossed double yellow lines to pass his 10-metre truck and trailer unit once or twice a day. Many were rental cars. One recent case was a locally-owned tourist bus. "I just think about survival," he said.

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Supplied A motorcyclist just squeezes in after passing a 10m truck and trailer on double yellow lines on SH6, near Kingston.

NZTA figures show there have been 209 reported crashes on the stretch of road in the last six years, resulting in five deaths and 86 injuries. Three of the deaths were in the last three months.

Supplied A car passes a truck and trailer unit on double yellow lines as it approaches the town of Kingston on SH6.

The NZ Transport Agency (NZTA) said it was working at installing rumble strips, improved signage and barriers at high risk locations on the highway between Kingston and Five Rivers.

Such measures did not always work, it said. The recent fatality crash in which the two Americans died was on a stretch of road that had rumble strips and double yellow lines.

Two weeks before the Americans were killed , Kingston resident Harpeet Singh, 25, was heading to work at Mitre 10 in Queenstown when he crashed head-on with a bus. Police said he was on the wrong side of the road.

SUPPLIED Two people died in this crash near Kingston.

Over the three months of summer last year, police had 610 complaints to their *555 reporting line from the stretch of Queenstown to Garston – the 64km at the northern end of the road.

"The road is in a shambles. It's a mess," said Kingston-based Wilson Contractors manager Athol Elliot.

His drivers were on the road every day carrying gravel from Southland quarries to Queenstown and saw shocking driving daily "and not just by tourists".

THE INDIAN WEEKENDER Harpreet Singh, 25, was killed in a car crash on SH6 south of Queenstown on October 14.

He was pushing for changes on the Devil's Staircase, where slow vehicles ended up with a line of up to 30 cars behind them travelling at 40kmh. Frustration built and drivers took any chance to pass those in front, despite the obvious risk.

He wanted NZTA to put more passing lanes in and said his crew has identified six suitable spots.

Otago Lakes Central road policing manager Glenn Wilkinson described the journey from Omarama through to Te Anau as "high risk".

DEBBIE JAMIESON/STUFF Senior Sergeant Glenn Wilkinson, area road policing manager for the Otago Lakes region, is encouraging drivers to stay safe this summer.

Wilkinson said crashes on the Devil's Staircase were often caused by people taking corners too fast. From Kingston to Five Rivers, drivers perceived more space and straight roads, so speeds increased. The result was people going over the centre line, cutting corners and losing control.

The crashes could be horrendous. "Whether a crash is an injury or a fatal is quite often a toss of a coin," he said.

Contract bus driver Bill Metherell saw people overtaking on blind corners daily.

Many visiting drivers had already had a 12-hour day driving from Queenstown to Milford Sound and sightseeing before starting the return journey, he said.

"It's 600km of demanding roads and people don't seem to have a clue in their heads of what they're setting off to do. By the time it's 7pm they're heading back to Queenstown and they're dozy, or sleepy or in a rush to get to dinner.

"People talk about it being a dangerous road but there aren't dangerous roads, just dangerous drivers."

He believed reducing the speed limit would help. "It couldn't be clearer. There's signs and yellow lines. You could put more signs out but people ignore them."

Wilkinson said police would be on the road in numbers this summer, relying on the "halo effect" to minimise the chance of crashes.