A Queensland Rail network control officer was not alerted by a SPAD alarm when a Brisbane suburban passenger train passed a stop signal after its driver was briefly impaired, an ATSB final report details.
During the morning peak on 24 May 2023, a suburban passenger train passed a stop signal between Brisbane's Fortitude Valley and Bowen Hills stations when its driver (who later tested positive for COVID) was impaired by a sudden sneezing fit.
The driver identified the signal as they went past it and applied the emergency brake, with the train stopping 64 m beyond the signal. The driver then made an emergency radio call to network control.
The next signal was also at stop, providing protection to the rear of the next train, which was about 300 m in front.
An ATSB investigation found the driver had acknowledged an automatic warning system (AWS) alert as the train approached the stop signal, but did not then recognise the signal at stop, or later recall acknowledging the AWS alert.
"This was likely influenced by the habitual nature of AWS alerts, which were the same for all types of restricted indications and frequently presented during traffic congestion, as well as the driver's brief impairment," ATSB Chief Commissioner Angus Mitchell explained.
"This and other incidents investigated by the ATSB have demonstrated the potential limitations of AWS alerts to prevent signal passed at danger (SPAD) events such as this one."
The ATSB's investigation also found that due to inherent constraints in operator Queensland Rail's signalling system, the network control officer was not alerted to the SPAD by a SPAD alarm, and would therefore not have been able to intervene.
In these situations, the final report notes, the emergency response is reliant on the driver self-reporting the SPAD to the network control officer, a control which is ineffective in scenarios where the driver misses the limit of authority.
"In most train-to-train collision scenarios, the accident is preceded by at least one train travelling through a stop signal," Mr Mitchell said.
"Eliminating these SPAD events is therefore a key focus for rail industry participants, in particular operators, towards reducing the risk of accidents."
The ATSB's investigation found Queensland Rail's risk register for SPADs did not assess the inherent constraints in the signalling system demonstrated by this incident.
"The ATSB considers a scenario where a SPAD alarm is not presented to the network control officer, and the driver is not aware of the SPAD, has not been considered in Queensland Rail's risk assessments," Mr Mitchell said.
The ATSB is subsequently recommending Queensland Rail reviews the risk associated with a SPAD in these circumstances and consider any risk controls that may be appropriate.
Queensland Rail continues to maintain the current risk control arrangements, in conjunction with the AWS functionality, to manage the risk of SPADs while the preferred engineering control of European Train Control System (ETCS) technology is being implemented. Until this occurs, the ATSB's recommendation says, the established risk will remain.
"These types of limitations should be eliminated where possible," Mr Mitchell said.
"Where that is not possible, the hazards they create should be considered in risk assessments related to SPAD and collision prevention."
You can find here the final report: Signal passed at danger involving passenger train TE43, between Fortitude Valley and Bowen Hills, Queensland, on 24 May 2023
