Out-of-control train carriage ran 1.5km through Sydney Metro tunnel in one of several safety incidents

A 30-tonne railway trailer transporting equipment on the Sydney Metro project ran uncontrolled for more than 1.5km through the half-built tunnel between Marrickville and Waterloo in July, Guardian Australia can reveal.

A whistleblower inside Sydney Metro told Guardian Australia it was one of a string of serious incidents that have raised concerns that safety has been compromised to meet deadlines and avoid the project going further over budget.

The carriage carrying wiring and cables kept rolling through the half-built tunnel until friction brought it to a standstill.

The incident was so serious that the regulator published a safety alert to the industry asking all train operators to check their carriages urgently.

It has now audited all rail equipment used by Sydney Metro.

The runaway was not the first serious incident on the Metro project. The whistleblower provided the Guardian with a list of occasions this year where workers had narrowly avoided being killed, while more came to light through further investigation.

February 2022: two collapses occurred during demolition work at a Parramatta car park, part of the Metro West project. Sydney Metro denied there was a risk to worker safety as exclusion zones were in place. SafeWork issued one prohibition notice and one improvement notice.