A Dublin teenager has taken to the airwaves to complain, after his grandmother was left standing on an Irish Rail service for three hours.

Zach McCarthy (13) from Blackrock in Dublin was going to visit his grandfather last weekend.

He says a siren went on the platform, indicating the service was at capacity, which saw a rush of people board the train.

Zach says a pregnant woman was also left without a seat for the journey.

He used his confirmation money to buy a ticket to travel to Cork with his grandmother, who is aged in her 70s.

"Everybody rushed on to the train, my granny was left standing for three hours because there were another like 30 people standing", he said.

"There needs to be a different policy and it's unfair".

"I told the man I paid for a ticket and I'm entitled to one (seat) - and he said 'No you didn't, you paid for a ride on the train'. I paid €34 for that train", he said.

"I feel that you shouldn't be charging €34 and not even get a seat," he added.

Zach told the Pat Kenny Show here on Newstalk, hosted by Shane Coleman, he has written a letter to the company about the incident.

Barry Kenny of Irish Rail says that day in particular saw very high demand - but he has apologised over the incident.