Rail passengers could be subject to border checks on services between the Republic and North in the event of a hard Brexit.
But passengers travelling on Enterprise services between Dublin to Belfast are not expected to endure lengthy delays, according to Irish Rail chief executive Jim Meade.
He said if border controls are required in the event of the UK crashing out of the EU without a deal, they will likely take place on board.
He also ruled out introducing additional time to allow for the checks, which could increase journey times.
"Our plan is to not disrupt the service," he said. "A hard Brexit is a worry. We've had several discussions with Translink (the Northern Ireland railway operator) around how it would operate.
"If we have to have Border checks, we would expect a methodology where customs officials come on board and do checks between stations. We won't provide time for Border checks. We have said we don't see the benefit of building in a half-hour stop for customs checks. The experience in Europe is hop-on hop-off."
He also said a hard Brexit could result in Northern Irish train drivers who work on services into the south being required to acquire a licence allowing them to operate in the Republic.
Train drivers operating in EU member states are required to hold an EU driver licence, meaning an Irish driver could work in France, for example, after the necessary training.
But Northern Irish drivers would no longer have this certification, if the UK leaves without a deal.
"Post a hard Brexit, that certification falls. They have a UK licence but in order to operate on our network they will need certification. It's not a huge issue. It's doable but it will involve effort and time," Mr Meade said.
He also said the railway company was working with the OPW about providing customs and inspection posts at Rosslare Europort to accommodate trucks coming off ships, truck parking, a dedicated Border control point for live animals and a public office with accommodation for staff.
It could take up to two years to provide the infrastructure, he said, but interim arrangements would be put in place.
"We're working with the OPW. It's taking a lot of time and planning and our intention is to keep the port open," he said.
"It has the potential to impact on business if we don't put in place arrangements. Long-term, we do need the facilities and there is an outline plan agreed. Brexit is taking time and effort to put in place contingency planning. We have to put plans in place," he added.