Double demerits now in force across Australia

Double demerits are now in force in parts of Australia as drivers hit the road for end-of-year holidays.

It's the first time in three years all borders have been down for the Christmas break, and the nation's highways are expected to be extremely busy - with police on high alert for any bad behaviour behind the wheel.

Here's what you need to know:

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NSW and ACT

The double demerit period in NSW and ACT will run for 11 days from Friday, December 23 until Monday, January 3.

During double demerit periods, double demerit points apply for speeding, illegal use of mobile phones, not wearing a seat belt and riding without a motorcycle helmet.

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Western Australia

The double demerit period in Western Australia is longer than in other states.

The operation will start on Friday, December 23 and run until Sunday, January 8.

Police will target several offences including speeding, drink or drug driving, failing to wear a seatbelt and child restraint, running a red light and the illegal use of a mobile phone.

Drivers can receive 14 points during the double demerit period for using a device designed to evade detection by a speed camera and driving a car in a manner to evade speed camera detection.

Queensland

Double demerits apply all year in Queensland.

People who repeatedly commit specific offences will receive double demerit points for the second or subsequent offence if the later offence was committed within 12 months of an earlier offence.

This doesn't just apply over the Christmas and New Year period, but at any time of the year.

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Victoria, South Australia, Tasmania and Northern Territory

These jurisdictions don't have double demerit periods at all.

But people are still urged to drive safely and carefully at all times - and police are likely to be out in force on the roads over the holiday period.