An elderly woman who fell in the street and cut her head travelled to hospital on a Luas because there was no ambulance immediately available.
The woman, who is in her 80s, fell at the Blackhorse Luas stop in Inchicore.
Staff immediately went to her aid and called an ambulance.
But they were told it could take more than 20 minutes to reach to the scene.
Luas staff then offered to take the woman to St James's Hospital by tram as it passes through the grounds on its way to the city centre.
Two ticket inspectors helped the woman into the hospital where she received treatment in the emergency department.
A witness said she had a large bump on her head after the fall.
"It was disgusting that she was treated like that. Everyone was upset about it," said the witness.
A Dublin Fire Brigade spokeswoman said it could not comment on individual cases, but added that with current resources, calls are prioritised according to clinical need, and all the ambulances were on more critical calls at the time.
A spokeswoman for Luas confirmed there had been an incident at Blackhorse in which a person received an injury after a fall and decided that travelling to hospital on the tram might be the quickest option.
Local representatives expressed their concern at the incident.
"My immediate reaction is one of horror," said Labour TD Eric Byrne.
"It's ironic that a Luas tram would act as a substitute for an ambulance and the staff of the Luas wouldn't be trained in dealing with head injuries.
"One doesn't want to undermine the value of what they did, but they're not paramedics.
"It's shocking that it would take 20 minutes for an old lady to have her injuries tended to," he added.
People Before Profit TD Joan Collins TD condemned the incident.
"No person should be left on the side of the road with their injuries because an ambulance isn't available," she said.
She also criticised the Government, saying the incident highlights a lack of resources in the health service.
Local Sinn Fein councillor Greg Kelly said the incident was "disgraceful".
"The Luas is great, but I would have always thought an ambulance with sirens on it would have got her there quicker," he said.