Runaway train in Hunter Valley 'worst-case scenario' for rail safety

In short:

Questions are being asked after a runaway train rolled downhill through the Hunter Valley for several kilometres with no-one on board.

The ABC understands the train reached speeds in excess of 60 kilometres per hour.

What's next?

The Office of the National Rail Safety Regulator is investigating what caused the incident.

Questions continue to be asked about how a fully laden coal train was allowed to roll without a crew for several kilometres through the NSW Hunter Valley.

An expert in transport management says the runaway train could have caused an extremely serious accident.

The ABC has been told the Pacific National coal train began rolling downhill with no-one on board during a crew change in the early hours of Saturday morning at Camberwell, between Singleton and Muswellbrook.

University of Sydney senior lecturer in Transport Management, Geoffrey Clifton, told ABC Newcastle Breakfast such incidents were "quite rare" outside of a maintenance setting.

"The worst-case scenario you can have on the network is a runaway train for obvious reasons," he said.

"The question is why wasn't there enough braking power … either the brakes failed, or there weren't enough brakes put on in the first place."

Australian Rail Track Corporation documents show Pacific National coal trains operating on the Hunter Valley line are typically between 1.296 and 1.541 kilometres long, and include between 82 and 96 wagons.

The unstaffed train travelled through at least one level crossing, but Steve Muscat, a director and principal engineer at consultancy Rail Confidence, told ABC Newcastle Mornings the boom gates would have come down.

"Thankfully they are automated and activated by electrical track signals," he said.

"It certainly would have activated."

Dr Clifton said coal trains had a brake on each carriage that connected with one control system.

"It's possible that the brakes failed somewhere along the line, which would lead to a runaway train," he said.

"It's also possible that the brakes weren't applied properly and that's where the investigation's going to look."

The Office of the National Rail Safety Regulator (ONRSR) said in a statement it was investigating the incident.

"The ONRSR has … deployed a team of rail safety officers, investigators and rolling stock specialists to the Hunter Valley where a fully loaded coal train has been involved in a runaway incident," it said.

"In addition to assessing and inspecting the scene, ONRSR is seeking information and documentation from the rail transport operator."

Pacific National, which hauls coal between the Hunter Valley and the Port of Newcastle, said in a statement it was taking the incident "extremely seriously".

The company said it would be inappropriate to comment on the incident or speculate on the potential cause.

Muswellbrook Shire Mayor Jeff Drayton said he would be meeting with employees to discuss the incident.

"At this stage, it's unclear if it was a human or mechanical error, or a combination of both," he said.

"Investigations are ongoing."

The ABC has been told the train travelled at speeds in excess of 60 kilometres per hour before coming to a stop several kilometres away at Glennies Creek.

Dr Clifton said the natural incline of the track was likely to have eventually brought the train to a standstill.

"It would've gone until something stopped it, usually another hill or if it triggers a derailing point," he said.

"If something goes wrong on the track,s it can be quite serious, which is why the [ONRSR] is going to be investigating this very closely.

"These things don't happen very often, so we need to learn from it every time it happens."