The reporter has raised a safety concern relating to the alteration of train automated warning systems.
The reporter states, drivers regularly alter safety controls by placing items (mostly stickers) over the automated warning system (AWS) buzzers. The purpose of the AWS is to prevent signal passed at danger (SPAD) incidents by alerting the driver when the train is approaching a yellow or red signal. The actions taken to muffle the noise level of the buzzers may potentially lead to an unidentified SPAD incident. It has been observed that the covering of AWS buzzers has occurred across the majority of the [Operator] fleet consoles. The reporter advises that AWS buzzers that are positioned under the console of the [train type] have also been altered in an attempt to muffle the noise.
The reporter finally advises, from a human factors perspective, some of the AWS buzzers are intolerably loud. The reporter is concerned that with differing levels of hearing across individuals, some drivers may not hear the buzzer when activated if they have been altered to reduce noise levels.
[Operator] acknowledges the reporter's concerns and the ATSB's interest in the matter.
The AWS system on the [fleet] is one of several systems in the cab designed to protect against driver incapacitation. The system generates two different sounds depending on the state of the signal. Where there is a potential for a SPAD due to driver incapacitation, the system is designed to apply an automatic emergency brake application if an alarm is not acknowledged. The signalling system is designed so that in most circumstances at least two alerts must be successfully acknowledged (that is, cancelling the emergency brake application) before a red signal is reached.
Where the driver is not incapacitated, it will be clear to the driver if they have not acknowledged the alert as the train will suddenly brake, which the driver can correct. A second (different sound) is generated by the system when there is no possibility of a SPAD. The only action for the train crew for this alert is to report when the sound is missing as a potential fault. Muffling the buzzer so that the driver missed the restricted alarm will result in an emergency brake application and not a SPAD.
In a SPAD event, if a driver does not hear and acknowledge the AWS alarm, the consequence is that the train will bring itself to a stop - which is the intended behavior of the safety system. The system is designed so that the driver can interrupt the emergency brake application to manage this risk.
The effect of stickers in these locations dulls the audible alarm of the automated warning system but does not block it entirely.
[Operator] periodically tests its [train] AWS sound test levels and as a precautionary measure, [Operator] will inspect its electric traction fleet over the coming weeks to ensure there are nil decals covering the buzzers.
[Operator] thanks the reporter for their concern and will be issuing an important operational notice to rail traffic crew that placement of stickers in these locations is not supported or authorised by [Operator], and any employee identified as being responsible is managed accordingly.
ONRSR confirms receipt of ATSB REPCON RR2025-00013, dated 2 July 2025, regarding alteration of train automated warning systems. ONRSR has reviewed the reporter’s concerns and operator’s response. ONRSR is satisfied with the stated actions the operator is taking to address the issue. ONRSR may seek further information from the operator at a future stakeholder engagement meeting.