Roundabouts - why do so many drivers fail to indicate correctly? The picture shows the intersection of Quarantine Rd and State Highway 6 in Nelson.

It's a mystery. Why do so many drivers fail to indicate correctly at roundabouts?

The latest evidence of the size of the problem comes from Horizons Regional Council. A committee meeting last week was told a one-hour survey of two roundabouts in Levin in September counted 227 drivers who failed to indicate correctly, out of a total of 404.

Waikato University chair of psychology Dr Samuel Charlton, whose areas of specialisation include road safety, said he wasn't aware of any research into the issue.

NZTA The correct way to turn right at a roundabout.

He did not know of any good data that showed what drivers were doing wrong, whether they were maybe indicating a turn when they shouldn't, or were failing to indicate their exit from a roundabout.

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NZTA The correct way to go straight ahead through a roundabout.

"Someone should really look and see," Charlton said.

"It's almost noteworthy when someone does it right, as opposed to all of the people who do it wrong."

Once the details of the problem were identified then it would be possible to see why it was happening. There might be a lack of knowledge by some drivers, or it could be because of the number of things drivers had to do sometimes.

Supplied A car drives up the wrong side of Bloomfield Tce in Lower Hutt, over a pedestrian crossing, enters a roundabout into the path of oncoming traffic, then heads up Knights Rd.

"It's a complicated little manoeuvre we do at roundabouts," he said.

Research could also include going through crash analysis to find out how much of a factor incorrect signalling was in "fender benders".

What was known about roundabouts was that they were generally good when it came to reducing the severity of crashes.

"If people do ... bump into each other they are going more or less in the same direction. No one gets t-boned at high speed, which is what can happen at traffic lights," Charlton said.

A little more was known about issues for cyclists at roundabouts. "That's not a problem of signalling, usually. It's a problem of drivers not checking all the way to the left where the cyclists hang out."

Roundabouts were not widespread throughout the world, rather they tended to be more usual in Commonwealth countries.

Hutt City recently made an effort to improve roundabout signalling, with police giving offending drivers a refresher course. Waipa came up with the "Hey mate, indicate!" campaign to try to get more drivers indicating properly.

A far less common risk at roundabouts is drivers going the wrong way but it did happen during peak time traffic in central Hutt City last week. The incident was caught on dashboard camera and an 18-year-old is to appear in court charged with dangerous driving.