Safety devices that shake the driver's seat when the driver falls asleep have been installed on Auckland buses.

Auckland Transport is trialling "eye-monitoring" technology in a bid to stop bus drivers falling asleep at the wheel.

Some New Zealand trucking companies already use similar devices, which sound an alarm and shake the driver's seat after a camera facing the driver detects that the driver has become distracted or closed their eyes for too long.

One truck driver previously told Stuff the technology saved his job - and possibly his life.

But a union which represents Auckland bus drivers has criticised the move to install the devices on buses, saying they shouldn't be necessary because bus drivers shouldn't be so tired they're falling asleep.

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First Union's assistant general secretary Louisa Jones said the union was concerned about the long shifts bus drivers were working on Auckland public transport routes.

SUPPLIED Auckland Transport is considering putting devices on buses that will shake bus drivers' seats if they start falling asleep at the wheel. But the union says the technology shouldn't be needed because bus drivers shouldn't be working such long hours.

"Even though you're only getting paid for eight hours you might be working for 14 hours because there's a long book-off period in the middle of the day."

Auckland Transport (AT) spokesman James Ireland said AT would trial "driver distraction management systems" on Go Buses for four months from November.

"The driver distraction management system detects if a driver's eyes are closed for a length of time that would indicate they are fatigued, it also monitors if a driver's head is turned away from the road while driving, which could indicate a driver is distracted.

"If the driver's eyes or head are away from the road for more than the set time an alert sounds and the seat vibrates. The monitoring station will also receive alerts so they can contact the driver to check how they are and if they need a break or further assistance to ensure their safety."

Using the devices was about preventing distraction as well as drowsiness, he said.

"AT's number one priority is safety."

GEORGE HEARD/STUFF Eye-monitoring cameras have been installed in vehicles by some New Zealand trucking companies, now Auckland Transport is considering putting similar devices in passenger buses.

Evidence showed drivers were most likely to be distracted or drowsy at the start of their shifts.

Jones said the union didn't support use of the systems and instead wanted to see drivers' working conditions improved.

"What is the point of driving someone so long that they're liable to fall asleep and then you shake them to wake them up? It's ridiculous.

"Bus companies are finding it more and more difficult to get people to become a bus driver because the hours are very unsociable, the job is dangerous and the wages aren't good enough."

In April, Stuff revealed that Auckland bus companies were having to put managers and office staff behind the wheel most days because they couldn't find drivers willing to do the job.

Jones also reiterated claims made by the union earlier this year that Go Bus drivers were working up to five-and-a-half hours without a break.

Jones said one bus driver, who was diabetic, had left his job because he felt that by going without sugar for such a long period he could be putting passengers in danger.

Ireland said bus operators managed the drivers' hours according to guidelines set by the NZ Transport Agency's Work Time Rule.

"NZTA investigates complaints alleging breaches in Work Time Rule and if the risk of driver fatigue is appropriately managed. AT works with the NZTA to assist and support any investigation into allegations of breaches."

An NZTA spokesman said it had investigated the shift duration issue raised by First Union and Go Bus had taken action to remedy it.