NSW Transport Minister Gladys Berejiklian said 85 per cent of South Coast line commuters surveyed supported the move, and it would now become permanent.

Quiet carriages are the front and rear cars of eight-car trains, and the rear car of four-car trains.

In these carriages, passengers must turn mobile phones to silent, move to another carriage to have a conversation, and keep the volume of headphones to a level where the sound can't be heard by others.

There are no signs in the quiet carriages and it is largely up to commuters to enforce the quiet rule.

Announcements are made at major stations, but this has posed some problems with passengers who cannot properly hear or understand the announcement and continue to talk loudly.

Member for Kiama Gareth Ward said signs would be installed on platforms alerting commuters to the rule, and he expected people would adapt.

"Obviously there will be announcements so people get used to the system," he said.

"It will become part of the commuter culture."

Mr Ward said the quiet carriages were not for everyone, including himself, so it was up to travellers to respect the distinction, and sit elsewhere if they wanted to talk.

He said the popularity of the scheme was what he had expected.

"Having travelled on trains for a large part of my life . . . I was not surprised," he said.

"There are many individuals like myself who like to talk to people around them.

"Quiet carriages are not for people like me," he said.

The quiet carriages are expected to be particularly helpful for commuters catching another hour's sleep on the way to Sydney.