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.

16 June: an escalator being installed at the new Martin Place station site fell four floors, narrowly missing workers. Sydney Metro said the contractor had appropriate exclusion zones in place. SafeWork issued four prohibition notices and required a demolition plan to be lodged for the recovery operation.

June: a labourer for a contractor on the Pitt Street site was seriously injured after a personnel hoist failed. The worker attempted to jump to a nearby landing, but fell nine metres. His injuries included a broken leg and pelvis. Sydney Metro denied union claims the contractor was not properly trained.

31 August: a Sydney Metro truck carrying heavy scaffolding nearly lost control of its load on the Cahill Expressway. Sydney Metro said the vehicle continued without incident to the Waterloo site, despite photos showing the load partially off the truck.

September: formwork collapsed at the Crows Nest station site. This incident is under investigation by SafeWork.

The Metro West line from the CBD to Parramatta could blow out by $3bn to a total of $27bn, and the City and Southwest line could cost $5bn more than the $12.5bn original budgeted, the Sydney Morning Herald has reported.

There is also pressure to speed up the project.

But the whistleblower said that was not the experience of those on the project.

In some instances, the whistleblower said, the seriousness of safety incidents had been downgraded to avoid them being reported to Safe Work.

The runaway train incident and the other rail-truck crash incident should have been reported as category A incidents, which require an immediate phone call to the rail safety regulator to enable inspectors to gather evidence, a spokesperson for the ONRSR said.

Sydney Metro reported them as Category B incidents, which requires reporting within 72 hours. The runaway took place on 16 July and was notified on 19 July.

The whistleblower said he was not alone in his concerns and that project managers had developed an informal network of sharing incidents and information to make up for the lack of information coming from Sydney Metro.

He said he felt the organisation was trying to keep the unions in the dark.

The CFMEU (NSW) said it was not aware of all the incidents in the tunnels.