Translink is engaged in discussions with Irish Rail over concerns an early morning Belfast to Dublin service is causing delays for commuters in the Republic.
The fears were highlighted in a letter from an Irish government minister.
Joe O’Brien, who is a TD for Dublin Fingal, wrote to the Taoiseach, Tanaiste and the Irish transport minister Eamon Ryan, saying the new timetable changes over the summer had impacted rail routes serving north Dublin and Louth.
The timetable change, made on August 26, means the Dublin Enterprise service is due to leave Belfast at 6am, which requires the Drogheda to Dublin line to alter.
While the timetable has changed, the service has yet to be fully implemented as currently those travelling from Belfast to Dublin on the Enterprise service have to board a bus to Newry, where the journey can continue via train.
However, last week the first Enterprise train testing took place at the new transport hub.
Translink said that the flagship service to Dublin will run hourly and will see 15 trains leave the travel hub for the Republic every day – a total of 30 running in both directions.
However, they have yet to confirm when the train services will operate from Belfast Grand Central station.
Earlier this year, the Belfast-Dublin service was impacted following line closures in Northern Ireland linked to the new £340m station.
In his letter, Mr O’Brien said: “What is especially problematic is a 30-minute gap at the peak morning period where there is no commuter service.
“This not only leads to a significantly decreased level of service but existing services have been concentrated over a shorter time, causing capacity issues on some trains and long delays.
“The changes have also reduced through-services, impacting commuters who travel south of the Liffey. With all trains now terminating in Connolly or Pearse, this adds to journey times and increases the risk of delays.”
He claims the new 6am service for the Enterprise has meant commuter trains operating from Drogheda to Dublin have had to move lines, causing delays.
“A delay or cancellation of the 6am Belfast service would go some way to alleviate some of these issues, while the [Belfast] Enterprise service is important, the knock-on effect on Dublin commuters is unacceptable,” he added.
“It is important to note that the previous first service out of Belfast was 6.50am. I am also led to believe that currently the relevant Enterprise service is starting in Newry (not Belfast) and it will be later in the year before it actually serves Belfast.
“In my 20 years using the commuter line I have never seen such a poorly implemented change and would request an immediate intervention to resolve the ongoing issues.
“To sum up, we are simply trying to squeeze too many services on to a single train track. We ultimately need additional track space.”
Irish Rail has apologised following the delays. Speaking on RTÉ’s Prime Time last night, Barry Kenny, the corporate communications manager of Iarnród Éireann (Irish Rail) said the timetable changes “haven’t been working the way it should have been”.
“We are sorry to our customers for what has happened,” he added.
A spokesperson for Translink confirmed they are currently in discussions with Irish Rail about the impact.
Passengers in the Republic were previously advised that departure times were proposed to change on many DART, Northern Commuter and Maynooth Commuter services in order to accommodate the extra Enterprise services.