THE Bombela Concession Company, which operates the Gautrain, is investigating why its rescue protocols failed yesterday and left commuters stranded for more than two-and-a-half hours.

This is the third time in just more than a week that trains run by Bombela have come to a halt because of technical problems. Last Monday they were stopped when train doors would not open at Marlboro station, and a day later there was a technical glitch with an overhead pantograph.

Yesterday the Gautrain came to a halt between Centurion and Midrand. A rescue train should have arrived within half an hour of it becoming stranded, Kelebogile Machaka, spokeswoman for Bombela, said yesterday.

But it had taken an "extremely long" time, she added.

The Gautrain had operated at about 90% last week with regard to train availability and punctuality, Ms Machaka said.

Last month, Bombela, which runs 249 trains a day, achieved 99,6% train availability and 98,6% punctuality. Globally, best practice for trains was to aim for 98% and 95%, Errol Braithwaite, a Bombela director, said yesterday.

The rescue train should have "coupled up" yesterday, connecting with the stranded train to pull it to the closest station with all the passengers on board, he said. But it was unable to connect and repeated attempts to couple up had caused much of the delay.

An investigation into the incident had not yet been concluded and Mr Braithwaite said he could not comment on why the coupling up had been unsuccessful.

"Plan B" if the rescue train fails to couple up is to send another replacement train.

Frustrated commuters tweeted furiously about the delay yesterday and posted photographs of themselves walking to the replacement train. Some likened it to the notoriously unreliable service of state-owned Metrorail.

"We have also tried to contact people who were on the train through social media so we can hear from customers what happened and learn what lessons can be learned ," Mr Braithwaite said.