Monday, November 25, 2024

Safety Message: Dark Signals and Mixed Mode Operations

An interoperability solution enables operators of trains equipped with signalling technologies such as ETCS and CBTC to realise the benefits of these systems as soon as they are deployed onto a rail corridor, while trains using existing technologies can still operate safely on that corridor. This situation results in what is referred to as “mixed mode operations”.

Different signalling solutions are available to enable trains to operate under mixed mode operations and all have unique characteristics and risks. Of the many different solutions available to facilitate mixed mode operations, one of particular interest to ONRSR is that which involves extinguishing the lineside signals (effectively creating ‘dark signals’) that a driver would normally see when they are operating under the authority of an ‘in-cab signal’ indication.

This safety message explains ONRSR’s expectations as to what a Rail Infrastructure Manager (RIM) would be required to demonstrate in terms of managing the risks associated with a signalling solution that facilitates mixed mode operations, and in particular dark signals.

‘Dark signals’ with indication lights

Different variants of the ‘dark signals’ solution include these dark signals being fitted with an additional indication light as part of the signal to confirm to the driver that they are to abide by the in-cab authority. This additional indicator light may take different forms, but it is illuminated so as not to be confused with a traditional signal that has ‘blacked out’.

Melbourne

On the Melbourne network there is a section of track with mixed mode operations where the dark signals solution has been implemented for the CBTC area where lineside signals were retained. In this application, when the signals are extinguished, there is no illuminated indication light. Instead, there is a static sign adjacent to the signal. This signage indicates that the signal is part of the CBTC area and that trains fitted with onboard equipment should follow the authority presented on the in-cab display.

As noted, there are many and varied solutions applicable dependent on the specific circumstances and as such the particulars of the Melbourne CBTC mixed mode section of track are unique to those circumstances. They should not be considered a reference case that can be applied to other locations to support a SFAIRP argument.

ONRSR’s expectations

In assessing any proposal for a dark signal solution in mixed mode territory, ONRSR will base its decisions on what is considered SFAIRP. Emphasising that any new proposal that relied solely on static non-illuminated signage (i.e. the Melbourne solution) would be unlikely to meet the SFAIRP requirements of the Rail Safety National Law without sufficient justification. The Melbourne solution represents a unique set of circumstances.

Without pre-judging any safety argument, ONRSR expects it would be difficult to justify ruling out the inclusion of some type of illuminated indication light or equivalent control to work in conjunction with dark signals to manage the risk to safety that drivers are not made sufficiently aware of the changed operation.

Given the status of various signalling projects around Australia, ONRSR strongly encourages industry to understand these expectations regarding dark signals and factor this into decision making processes.

For further information or to discuss this matter, please contact your local ONRSR office