Demand for the new millennial railcard has crashed the website on the first day of nationwide sales.
The one-year railcard for 26 to 30-year-olds will cost £30 and offer a third off most fares in England, Wales and Scotland.
It first went on sale nationwide at about 07:30 GMT but “exceptional demand” caused the website to fail.
Delays of up to two hours have persisted into the afternoon with some still struggling to get online access.
Only 10,000 railcards are being released during the trial.
“This morning, when the 26-30 railcard trial began, the National Railcard website was receiving 12 times the normal number of visitors. We were prepared for demand to be similar to that of previous trial launches,” said a spokeswoman for the Rail Delivery Group, which represents the train companies and Network Rail.
“Due to the unprecedented demand we have been working with our suppliers throughout the morning to further increase the capacity on the website to create a better experience for our customers. We recommend that customers continue trying the National Railcard website, and keep an eye on @_Railcards Twitter and Facebook pages for updates.”
The group had earlier apologised for the problems.
Some passengers have been expressing their irritation at the problems.