Plans for a 10 minute DART service in Dublin are being described as "ambitious".
Transport Minister Shane Ross says they will come on stream in the next six months.
But Unions are warning that drivers still have not signed off on it.
Dermot O’Leary is from the National Bus and Rail Union says there are still issues.
"There is logistical and operational problems here as well," said Mr O’Leary.
"We don't have the extra coaches for a 10 minute DART service. It could be a case that the current eight-piece coaches could be reduced significantly to two four-pieces for example.
"You might have a situation where people might have a 10 minute service but they might not be able to access the service at a time they want to."
- Digital Desk