Not only will double demerits for the Australia Day long weekend apply from tonight until midnight on Sunday, January 29, but school zones will be back in force from Friday.

Roads and Maritime Services has warned motorists double demerits will apply for speeding, seatbelt or helmet offences.

A spokesman said the first gazetted day of term one for NSW schools was Friday and 40 km/h zones would apply.

"While many students may not return to school until January 30, the first gazetted day is January 27, when double demerits will be in force for the Australia Day long weekend," he said.

"Not all motorists will know if the school they are driving past is having a pupil-free day or if students are at school, which is why all 40 kilometre school zones are consistently applied.

"Motorists can check traffic conditions with the transport management centre on 13 27 01 or at the website: livetraffic.com