Metro Trains, which operates 210 six-carriage trains across 869 kilometres of track in Melbourne, is investigating the fault in its computer control system that led to its entire rail network being shut down on Thursday afternoon.
All suburban and some regional trains came to a standstill at 4:00pm -- mostly at stations, though some were grounded in between stations -- for about an hour, causing lengthy delays during peak period.
The failure of the AU$88 million Train Control and Monitoring System (TCMS) -- which was switched on in 2014, 15 years after it was initially proposed to improve efficiencies in the public transport system -- meant network controllers could not see where in the rail network the trains were, and had to shut operations down temporarily for safety reasons.
The train operator's CEO Mike Houghton told 3AW radio on Friday morning that the cause of the fault remained unclear, including "how the system failed to the point where the backup failed".
While some reports suggest that Metro had ruled out hackers as the cause of the system failure, Metro did not confirm or deny that to ZDNet.
Instead, Metro Trains told ZDNet that an investigation was launched yesterday with "engineers working right through the night".
"The systems have multiple protections and redundancies in place and the investigation will get to the bottom of why these did not keep the network running," Houghton said.
"I am personally making sure we understand every detail of what happened last night and I'm sorry people were delayed."
In November last year, Victoria's auditor-general concluded in its report [PDF] that there were "significant weaknesses" in the security of Metro's and V/Line's control systems, unhelped by "inadequate" governance by Public Transport Victoria (PTV).
The state's economic watchdog found that there was a lack of understanding between PTV and train operators about ownership, roles, and responsibilities; no strategic direction to develop minimum security requirements for control systems; inadequate risk and compliance management processes; and limited progress in addressing the findings of its 2010 audit.
The auditor-general had warned in its report that potential cyber attacks could shut down train services for extended periods of time, inflicting economic harm on the state.
The train operator announced on Twitter that it will refund commuters affected by the disruption.
While its current compensation system operates on a case-by-case basis where commuters are required to fill out forms -- customers can only claim compensation based on the overall performance of the network during any month, not for single incidents -- Metro said passengers that tapped on between 3pm and 7pm will be automatically reimbursed for the cost of their two-hour fare.
Both myki money and myki pass passengers travelling on a full fare will be reimbursed AU$4.10, while concession travellers will be refunded AU$2.05. Metro said the refunds will be processed automatically within 30 days.
At present, Metro is required to run 98 percent of services each month with a punctuality target of 88 percent to avoid having to compensate customers.
The Victorian government was at the cusp of extending its contract with Metro Trains by seven years, provided it accepts tougher performance targets. It is unclear at this stage whether yesterday's event will impact its decision.
Victorian Transport Minister Jacinta Allan called the network-wide outage "completely unacceptable", adding that its contract with Metro stipulates that the train operator can be fined for such incidents.
"The government has already made its view crystal clear," Allan told ABC radio. "We expect a higher performance standard on the next round of contracts. We have written those requirements into the tender documents."
"There are mechanisms under the current contract that allow [Public Transport Victoria] to put a penalty on the operator.
"But we want to go about strengthening the performance so these sorts of issues do not happen."
The transport minister also criticised ridesharing service Uber for tripling its surge pricing for commuters impacted by the disruption.
"Taking advantage of people in a difficult circumstance is not a way to run the business," Allan told ABC radio.
ZDNet reached out to Public Transport Victoria, but did not hear back by the time of publishing.
Updated 7.30 am AEST 18 July 2017: Metro revealed how customers would be reimbursed for the disruption.