Windows will be kept open on trains this winter to prevent the spread of COVID-19.
Around a quarter of Irish Rail's fleet have windows that open manually - with the rest equipped with air conditioning.
On those trains that do have windows, passengers are being advised to wrap up on board during the colder weather while windows are kept open.
Irish Rail spokesperson Barry Kenny told Newstalk Breakfast it's an additional step on top of other measures, such as limited capacity, mask wearing and social distancing.
He said around 75% of train carriages don't have openable windows, but the majority of DART carriages and commuter carriages in the Cork and Limerick areas are among those that do.
He explained: "Obviously, the key measures remain the same on public transport - wear face coverings, only sit on the unmarked seats, and retain distance.
"This is an additional guidance to customers. Obviously there will be days when weather conspires against this, but we are into a season where people will be wrapping up I suppose more usually when they commute.
"We'd stress again that people should only be travelling at level three [restrictions] and any further levels above that if their journey is essential."
He stressed windows remaining open not a regulation, but passengers will be asked to follow the advice to aid ventilation.
Mr Kenny said compliance with the COVID-19 rules has been high, with well over 90% of passengers wearing masks - although he pointed out a small number of people in community will be exempt from having to wear them on public transport.