Calls have been made for a permanent rail connection between Londonderry and Dublin following the successful one-off service for the Pope's visit to Ireland.
Translink ran the six-carriage, 400-seater train that left Derry on August 26 for Connolly Station - only the third time in recent years the service has been available.
The Into the West railway lobby group has said there is no reason why Translink and Irish Rail could not make this service a permanent fixture.
However, Translink has argued there would be "limited demand" - which campaigners strongly refute.
Into the West member Jim McBride said: "We had to fight to save the rail line between Derry and Belfast after Translink said there was no demand - and last year there was a 40% increase in traffic since the introduction of the hourly service.
"Translink told us if an upgraded service was introduced there would be 25% increase in traffic in 25 years when the reality is there has been a 200% increase in traffic in five years.
"So I do not accept that there would be limited demand for a service between Derry and Dublin, because Into the West has proved time and time again, if the service is there, it will be used.
"This direct service last weekend meant that people leaving Derry arrived in Dublin in well under four hours, but currently anyone travelling from Derry hoping to go to Dublin has a wait of at least more than two hours for a connection."
Mr McBride said simple adjustments to the timetable would allow passengers arriving in Belfast from Derry to get a connection to Dublin.
"The first train leaving Derry in the morning arrives in Belfast at 8.15am, which is too late to catch the 8am Enterprise," he said. "So it doesn't take a rocket scientist to work out a timetable adjustment, which would be easy for Translink to do, would accommodate passengers in Derry wishing to travel to Dublin.
"Ideally and what we have been campaigning for over the past 15 years, is a direct line where passengers would not need to get a connecting train in Belfast.
"It doesn't need additional infrastructure, unlike the A5. Translink have the trains, all you have to do is extend the hourly service so that when it gets to Belfast it continues on to Dublin.
"The line from Belfast to Dublin is double tracked throughout, so it is very easy to operate a more intensive service if they had the will - but Translink don't have the political will to upgrade the service."
A spokeswoman for Translink said: "We run hourly train services from Derry-Londonderry to Belfast, from where our customers can board the Enterprise to Dublin.
"Any change to the cross-border timetable would require significant alterations to the Irish Rail, Northern Corridor timetable, which is currently heavily congested.
"Based on current passenger figures, we believe there would be limited demand for a direct route from the North West to Dublin.
"Where there is significant demand for particular event trains, we are happy to give this due consideration."