Absolute Signal Blocking (ASB)
ASB works on the principle of rail signals being set to stop with blocking facilities applied to exclude rail traffic from the work area. Within the rule there are several options to provide protection, including:
- Having two controlled absolute signals set to stop with blocking facilities applied or
- Having one controlled absolute signal set to stop with blocking facilities applied and
- Removing an ESML/EOL key, or
- Securing points to prevent access, or
- There being an easily reached safe place available and providing a lookout.
It is important to note that the rules provide two layers of protection. This provides a buffer area so that if a train that inadvertently passes the first blocked signal, it does not immediately enter a worksite location. For example:
Figure 4: ASB – Two consecutive controlled absolute blocked signals

Figure 5: ASB – One controlled absolute blocked signal and points secured

Figure 6: ASB – One controlled absolute blocked signal and Lookout

The ASB rule has the facility to allow the protection to be temporarily suspended in order to run rail traffic through the work area, provided certain assurances are gained. When rail traffic has left the work area, the ASB may be re-established. This facility was not used in relation to the work involved in this incident.
Within the ASB rule, there was also the facility to be able to clear signals being used for ASB protection to run rail traffic on an alternative route. This facility required the PO and the signaller to agree about the movements and make sure the worksite is clear of the alternative route. Other than these brief instructions, there was no other guidance in the rule, procedure, or other material to help make decisions when this facility in the rule was used. Sydney Trains withdrew this facility from the Network Rules on 16 October 2019, the day after the Westmead incident. This was achieved by issuing a temporary amendment document known as a Safe Notice Telegram 2019-1047.
The telegram stated:
‘ABSOLUTE SIGNAL BLOCKING (ASB) UPDATED REQUIREMENTS
Effective from 1800 hours, Wednesday 16 October 2019
In exception to NWT 308: Absolute Signal Blocking, when blocking facilities have been applied to exclude rail traffic from a portion of line, blocking facilities MUST not be removed to allow signals to be cleared for an alternate route. Blocking facilities MUST remain applied while the ASB is in force. These requirements will also apply when blocking facilities are applied to signals that are used to exclude rail traffic from a portion of line in accordance with NTR 432: Protecting activities associated with in service rail traffic.’
In December 2020, Sydney Trains introduced rule and procedure changes for ASB that permanently prohibited the clearing of the signal immediately protecting the worksite for the purpose of running a train on an alternative route.
Protection methods under ASB and their principle of operation
Basic principles of protection
The basic principle of protection under ASB is that a signaller will set and maintain one or more signals at stop to prevent rail traffic from intruding into the work area. This is achieved through a mutual arrangement of understanding between the PO and the signaller about the location of the work, the signals needed to protect the work and the choice of which option is used from the choices available within the rule.
The critical element of the protection measure is that someone remote from the work area is responsible for the function of setting and maintaining the signals at stop. This is what stops a train from entering the work area. For the most part, the workers on the track have no control over the status of the protecting signals – they rely upon the competence, capability and diligence of the signaller to ensure the protection is set and maintained for the duration of the work.
Clearing signals for an alternative route
When the ASB rule permits the same signals providing protection to be cleared in order to run rail traffic through an alternative route, it introduces a potentially conflicting objective that must be carefully managed to avoid the situation that occurred in this incident. The ASB rule, as it was on the 15 October 2019, provided almost no direction for those involved in managing the protection and how to deal with this potentially conflicting objective.
The extract from the rule NWT 308, as it was on 15 October 2019, said the following:
‘If protecting signals need to be cleared for an alternative route, the Protection Officer and the Signaller must agree about the movements and make sure that the worksite is located clear of the alternative route.’
The associated procedure NPR 703 Using Absolute Signal Blocking had no direction or guidance at all about how to manage this activity.
Detecting rail traffic approaching the worksite
Workers on track using ASB are also reliant on a signaller remote from the work area correctly identifying that there is no rail traffic closely approaching the worksite before the protection is approved and workers enter the danger zone.
A worker was fatally injured at Kogarah, NSW, in 2010 when a signaller did not detect the presence of a train between the protecting signals and the worksite in time to warn the workers. After the protection was implemented the workers went on track and the then train entered their worksite, striking and fatally injuring a worker.
The NSW Office of Transport Safety Investigations (OTSI) compiled a report about that fatal incident and the findings included how poor practices relating to signal box management contributed to the accident.
This is an example of the safety of the workers on track being a joint responsibility, including a worker who is remote from the worksite, who has a number of other responsibilities and distractions that can lead to errors, mistakes and omissions from this task.
Alternate methods of protection
Rail systems across the world have adopted technologies and practices that place the protection of the work on track in the hands of those doing the work, and who bear the risk of being struck by a train. This includes;
- devices to activate track circuits at the worksite to put protecting signals to stop
- switches on signals that allow a worker to set and maintain a signal to stop
- automatic train warning systems that detect approaching rail traffic and warn workers to move to a place of safety.
Sydney Trains have projects in place that either are under trial or in implementation phase that seek to introduce technologies that provide greater control for worksite protection.
This program is called the Enterprise Track Worker Safety (ETWS) Program. These projects and trials are currently in various stages of progress and development. Use of protection systems that look to eliminate the human error in areas like miscommunication, distraction or performance are to be encouraged.
A device that activates the track circuit of the protecting signal, or a switch that acts on the signal itself to place it at stop, would likely have prevented this incident, as the activation of this type of protection would be in the control of the Protection Officer with the work group. The Protection Officer was with the work team and would be very unlikely to clear a signal that would knowingly allow a train to enter their own work area.
Operating arrangements at Granville signal box
Rosters and meal breaks
Both panels in the Granville signal box are attended 24 hours a day, 7 days a week by a signaller for the purpose of routing trains through their area of control. A relief signaller is present on all shifts to provide coverage for the two signallers rostered on to the panels. The table signaller provides meal and comfort break relief and administrative support to the operating signallers in the form of processing various operational documents that are circulated daily in the Sydney Trains network.
Night shift at Granville signal box runs from 2135 each night to 0535 the following morning. The arrangements for staffing the panels are contained in a document called ‘Table person duties Granville Box’. The document is not published anywhere within the Sydney Trains electronic document management system. It is in hard copy only.
The document is not signed, approved or authorised by any Sydney Trains line management and has no document control or numbering, however it did have currency with the signallers in relation to the operating arrangements.
The document indicates that each signaller has two one-hour meal breaks per eight hour shift on day and afternoon shift. This document does not address the meal break and coverage arrangements for night shift. The document only shows meal breaks and panel coverage for day and afternoon shifts.
Figure 7 – Table Person Duties Granville Box

Source: Sydney Trains
The signallers at Granville signal box therefore had no guidance, direction or other instruction about how and when meal breaks should be taken on night shift or how and when coverage for the signalling panel should be arranged. It was essentially a self-managed function.
On the night of the incident, the GW signaller started work on night shift at 2135 and immediately went on a two-hour meal break. The signaller GT was then required to work on the Westmead panel from the start of the shift to provide a two-hour meal break relief for signaller GW.
At interview, the Sydney Trains line manager advised that it was not normal practice for signallers to commence their shift and immediately have a two-hour meal break. The Sydney Trains line manager advised at interview that two-hour paid meal breaks are not the common practice for Sydney Trains signallers, however this is what occurred on the night of the incident.
Supervision and work arrangements in Granville signal box
At around 2200 hours the signaller GG, rostered to be working the Granville panel, decided they would leave the panel and sit at the desk at the back of the signal box normally reserved for the GT, or table person.
The signaller GG did some of the work normally done by the table signaller, including processing Special Train Notices. The signaller GG also marked some training papers that they attended to as part of their role as a signaller trainer. Signaller GG left the control room at around 2300 to go to the meal room to prepare some food, leaving signaller GT alone in the control room.
This meant the GT signaller was managing both signalling panels for over one hour prior to the ASB incident at Westmead, and for a period of around ten minutes was the only person in the control room out of a team of three. The GT signaller is recorded as answering operational calls for both panels until the incident happened at 2304.
The role and responsibilities of signallers are documented in Network Rule NGE 234 Responsibilities of Signallers.
These responsibilities include:
- Safe operation of signalling equipment
- Responding to signalling faults, failures and warning alarms
- Authorising and issuing procced authorities, work on track authorities and methods
- Obtaining authority from the Sydney Trains Rail Operations Centre (ROC) to operate unscheduled rail traffic like defective trains, trains being worked out of service, empty trains being relocated and light engine movements
- Dealing with train delays and incidents.
The signallers roles are full time rail safety workers and the signalling panels are attended 24 hours a day, including on night shift. There is still rail traffic at night, including late night passenger and freight trains, and there is normally maintenance activity conducted at night. This warrants the full time attendance of signallers on both signal panels with rostered relief.
No explanation was offered by Sydney Trains for the unapproved absence of signaller GG. At interview, the Sydney Trains line manager considered the act of a signaller leaving their post without normal relief a code of conduct issue. There was no indication this matter was addressed as such.
Sydney Trains have a procedure that generally manages signal box operations, ‘Signal box management procedure’.[6] The procedure was originally issued in 2015.
The procedure covers generic issues including:
- Responsibilities of signallers
- Operation of signalling equipment
- Communication and supervision
- Administration and safety equipment.
The signal box management procedure does not have a recognised document number to indicate it is part of the Sydney Trains document management system. The procedure is shown as managed by the Compliance Standards Manager and approved by the Network Operations Manager.
The procedure does not mention how internal operational coverage is managed at individual signal boxes. It does not mention meal breaks or the role of relief signallers during their shift. Given the absence of any direction in this procedure, and the unauthorised nature of the Granville signal box document, Sydney Trains did not address this important aspect of network operations within their established management system.
Fatigue management for signallers
This Sydney Trains rostering and fatigue procedure included eight rostering principles to be observed in order to reduce or manage the cumulative effects of fatigue. These eight rostering principles, and a description of these principles, are reproduced below from the Sydney Trains procedure:
Principle
|
Description
|
Acclimatisation
|
Workers new to shift work and those returning after an extended period of annual or sick leave should not be rostered on night work or an early morning start for their first shift. When on leave, human circadian rhythms quickly re-establish a pattern of sleeping at night and being active during the day. Returning to night or early morning starts may be difficult, a bit like ‘Mondayitis’.
|
Shift length
|
The length of a shift should not exceed 12 hours including overtime, especially if it involves a night shift. Human performance declines significantly when people have been working for 12 hours or more, especially where work is done at night or in the early morning.
|
Total hours worked
|
Aim for no more than 48 hours per week including overtime, which can be averaged across the roster cycle. The risk of fatigue increases towards the end of a week/roster cycle. This is because a sleep debt has accumulated. Limiting the number of hours worked in a week or roster cycle, provides time off to recover and repay the sleep debt.
|
Limit night shifts and early morning starts
|
Aim for no more than: • four consecutive shifts where 12 hour shifts are worked • five consecutive shifts where 10 hour shifts are worked • six consecutive shifts where 8 hour shifts are worked. Working a series of night/early morning shifts disrupts circadian rhythms and leads to accumulation of a sleep debt.
|
Break during a shift
|
Schedule frequent breaks especially during a night shift or if the work involves sustained mental or physical activity, if local arrangements allow. Breaks during a shift provide workers with an opportunity to rehydrate and get a short rest. Breaks during a shift may be rostered or managed informally, depending on local arrangements and the nature of the work.
|
Break between shifts
|
Aim for at least 12 hours from the end of a shift and the start of the next shift. Industrial agreements may allow for less than 12 hours, however, to reduce the risk of fatigue, a minimum of 12 hours break is needed. Breaks between shifts need to allow enough time for recovery and sleep. Night shifts may need longer breaks between shifts. This is because workers will need to sleep during the day when it is difficult to get good quality sleep
|
Breaks between cycles
|
Make sure there are adequate breaks between shift cycles. For example: • Two days off in a 7 day shift cycle • Four days off in a 14 day shift cycle • Eight days off in a 28 day shift cycle. Days off should be a minimum of two consecutive days. Evidence indicates shift workers need at least two consecutive nights sleep per week to enable them to report to work feeling refreshed.
|
Shift cycles
|
Schedule consistent start times where possible, or if rotating rosters are used, shift start times should move in a forward rotation i.e. morning-afternoon-night. Consistent start times can help shift workers get into a routine. Where rotating rosters are used, there is evidence that a forward rotating roster allows shift workers to delay sleep and wake up later. This is easier to do than going to sleep earlier or waking up earlier.
|
The planned, or master, roster and shifts actually worked for the period from 6 – 19 October 2019 for signaller GT is included in the table below.
Date
|
Planned shift times
|
Actual shift times
|
Hours worked
|
Time until next shifts
|
6 October 2019
|
1335 – 2135
|
1335 – 2135
|
8
|
48 hrs
|
7 October 2019
|
0000 – 0000
|
0000 – 0000
|
0
|
|
8 October 2019
|
1335 – 2135
|
2135 – 0535
|
8
|
16 hrs
|
9 October 2019
|
1335 – 2135
|
2135 – 0535
|
8
|
16 hrs
|
10 October 2019
|
1335 – 2135
|
2135 – 0535
|
8
|
8 hrs
|
11 October 2019
|
1335 – 2135
|
1335 – 1735 (half shift)
|
4
|
20 hrs
|
12 October 2019
|
2135 – 0535
|
2135 – 0535
|
8
|
16 hrs
|
13 October 2019
|
2135 – 0535
|
2135 – 0535
|
8
|
16 hrs
|
14 October 2019
|
2135 – 0535
|
2135 – 05:35
|
8
|
16 hrs
|
15 October 2019
|
2135 – 0535
|
2135 – 0535 (incident 2303)
|
8
|
Off roster post incident
|
Five of the eight rostering principles were not met in relation to the roster of signaller GT in the eight days leading up to the incident. The five principles, and the nature of the departure from these principles, are outlined below.
Rostering principle
|
Departure from principle during this incident
|
Limit night shifts and early morning starts
|
From the 8 October to 15 October 2019, the signaller was rostered for eight consecutive shifts, seven of which were night shifts.
|
Break during a shift
|
One continuous shift break was rostered for the shift
|
Break between shifts
|
11 October 2019 there was a break of eight hours between shifts
|
Breaks between cycles
|
7 October 2019 was a single book off shift
|
Shift cycles
|
11 October 2019 backwards rotation of eight hours
|
According to the Managing Shift Work and Rostering procedure, when departures from these rostering principles occur, line managers must intervene and put in place measures to try and correct the situation. The line manager for signaller GT was unaware of the departure from these rostering principles, and therefore did not put measures in place as required by the procedure. The line manager for GT had not undertaken the mandatory training course ‘Fatigue Management for Managers’.
Sydney Trains acknowledged in their internal investigation report that the requirements for the procedure Managing Shift Work and Rostering were not being followed. Sydney Trains adopted a recommendation from their internal report as follows:
‘Review why the requirements of SMS-08-OP-3128 Managing Shift Work and Rostering, in relation to the diverting from Rostering Principles, are not being followed and determine appropriate corrective actions. In particular:
· the process for identifying and managing exceptions to the rostering principles with day to day operations (recording exceptions and capturing controls that are identified as a result);
· who has completed the required fatigue training to ensure understanding of the rostering principles;
· reporting exceptions to rostering principles; and
· the processes around the implementation of the Network operations – fatigue risk management checklist and its integration with the SMS.’
At interview, the signaller GT stated that they were well rested for the shift prior to the incident. Signaller GT recounted how they had an effective rest regime at home when working night shift and had obtained sufficient rest, had slept as usual from about 0830 to 1500, and felt fit and able to carry out their shift.
It is unknown whether the amount of sleep was sufficient to allow for recovery from the seven consecutive shifts. It is possible that the signaller GT was affected by the cumulative effects of fatigue given the deviations from five rostering principles leading up to the day of the incident. However the evidence is not definitive and it is not possible to ascribe fatigue as a contributing factor with any certainty.
Use of bio-mathematical fatigue scores
Sydney Trains employed fatigue modelling (using FAID[7]) for roster design and to ensure that employees were provided with adequate rest opportunity between shifts. Bio-mathematical models attempt to predict the effects of different working patterns on subsequent job performance, with regard to the scientific relationships among work hours, sleep and performance.[8] FAID ‘assigns a recovery value to time away from work based on the amount of sleep that is likely to be obtained in non-work periods, depending on their length and the time of day that they occur.’[9]
That is to say, FAID does not predict fatigue per se but rather predicts a sleep opportunity, demonstrating only that the organisation has provided employees with an adequate opportunity to sleep, producing a work-related fatigue score.[10]
The FAID score is a single number based on a zero to above 120 range. The number ranges and descriptors are given below:
- Standard: 0-40
- Moderate: 40-80
- High: 80-100
- Very High: 100-120
- Extreme: above 120
The Sydney Trains Operations Manager West/Illawarra was responsible for the planned shift work roster for signaller GT. According to the Operations Manager they would only conduct a risk assessment when the FAID score exceeds 100. The FAID score on the day of the incident was calculated by Sydney Trains as 93. There was no consultation with signaller GT about the planned shift work roster. Departure from the rostering principles, as occurred in this case, did not trigger any action by the line manager related to managing the potential fatigue of the signaller GT.
Sydney Trains have conducted a review of the use of the FAID score as it related to this case. They found that there was no documented rationale for the use of a FAID score exceeding 100 as a trigger for risk management actions.
FAID, along with other bio-mathematical models, is a useful tool to account for hours of sleep opportunity provided, thereby providing an indication of fatigue exposure across a group of employees. It cannot account for the hours of sleep actually achieved by individuals, nor for the quality of that sleep. These additional factors necessitate the use of multiple layers of controls to manage fatigue-related risk.
As a result of inconsistencies with the application of rostering principles Sydney Trains have recommended a review of their procedure for Managing Shift Work and Rostering. In particular:
- The process for identifying and managing exceptions to the rostering principles with day to day operations (recording exceptions and capturing controls that are identified as a result);
- Who has completed the required fatigue training to ensure understanding of the rostering principles;
- Reporting exceptions to rostering principles; and
- The processes around the implementation of the Network operations – fatigue risk management checklist and its integration with the SMS.
Safety Critical Communication
The communication between signaller GT and the Protection Officer
Signaller GT and the Protection Officer discussed the need to divert trains around the work area, however neither worker identified that the intended route through 727 would intrude on the worksite.
The lack of direction in the rules and procedures about how to manage this conflict contributed to the error. The error was likely compounded by an assumption from Signaller GT that the work was taking place further west at Westmead platform. This assumption was based on previous work on track activity, like track cleaning, which regularly took place through Westmead platform.
During the period of the conversation between the signaller GT and the PO to establish the ASB, signaller GT was regularly interrupted by phone calls related to the Granville signal panel, which the signaller GT was operating as well, because signaller GG had vacated their workstation.The signaller was performing multiple tasks in ensuring normal train running was occurring, monitoring multiple computer monitors, and ultimately attending to the request for worksite protection.
The communication requirements in NGE 204 require that interrupted communications must be restarted, however the signaller GT and the PO resumed their conversation after the interruption rather than restart it.
There was no advance notification to the signaller about the intended work, and its consequent impact on train running. An improvised train operations plan needed to be implemented. This added to the workload of the signaller and was likely a contributing factor to the error in assuming the workers were located clear of 727 points. The signaller GT misunderstanding of the position of the workers on track and the error in routing the train was likely the result of the cumulative effects of fatigue, magnified by the increased workload.
The lack of direction in the rules and procedures about how to properly identify the actual location of the workers within the area protected by the ASB, compounded by the signaller GT’s assumption about the location of the workers, led to the error of allowing the train 133U to pass protecting signal GE 463 and enter the worksite.
Planning of work in the Sydney Trains network
Sydney Trains Engineering and Maintenance Division employ several thousand people, including maintenance and upgrading staff, performing a multitude of tasks in and around the rail corridor. Sydney Trains also employ numerous contractors performing work on or around the track. Other organisations like Transport for NSW and Sydney Metro are also doing works in and around the rail network.
Many work activities are undertaken within a planned possession regime when occupation of the track is planned in advance and train operations are altered or replaced with buses. This work is advertised, and significant work goes into its delivery, including the altered train working arrangements.
In May 2020, Sydney Trains implemented the Access Pre-Advice system, (APS). This system is regarded as a planning and registration system, not a safety system. The purpose of the APS is to require work outside of a Local Possession Authority to be planned and logged into the system four days in advance, so that Network Operations have some visibility of the intended work and can plan for it.
In the period 20 May to 20 June 2020, there were 1063 applications for Absolute Signal Blocking in the Sydney Trains Network as recorded in the APS. Not all of these requests would result in train diversions, however, this figure illustrates the amount of unannounced work that Network Control Officers had to deal with in the Sydney Trains network prior to the introduction of the APS.
Sydney Trains also have a worksite protection planning system called the Corridor Safety Centre (CSC). This system requires the Protection Officer to contact the CSC and have their protection arrangements reviewed and validated before work commences.
In April 2021, Sydney Trains announced a trial of the integration of these two systems at Waterfall in NSW. This trial may introduce improvements to the process of planning and delivering worksite protection in the network.
At the time of the incident in October 2019, a significant proportion of the work on track that occurred in the Sydney Trains network was done with no prior knowledge of, or advice to, the Operations Division. In this incident, the first knowledge that the signaller had that the work was to occur was when the PO2 called Granville signal box to request the ASB.
There was no evidence available to indicate that the impact to train operations from the proposed work was considered by the Engineering and Maintenance Division. The effort was only put into determining the worksite protection required to permit the work to occur. Any resulting change to train operations is therefore a responsibility that is handed to the signaller to organise, with no advance notice.
Even a relatively small job like the WTSA inspections can cause train operations disruption, because of the need to exclude trains, and therefore, divert trains from their normal timetable. Diversions mean trains are not on their normal rostered path, stopping patterns are altered because different platforms need to be used for passenger working and the volume of services get compressed from two tracks to one.
Passenger information must be dispersed, station staff need to be informed and other adjoining signal boxes need to be advised of the altered train running arrangements. A decision to grant an ASB for a relatively simple task of taking track measurements can have a large effect on the network.
Because the WTSA inspections work was not known to the signaller, the signaller had to devise an improvised train operations plan, with little time to consider the implications of what was being planned. The signaller also had to attend to the other normal train running activities associated with the signal box on those tracks unaffected by the ASB.
The lack of an integrated planning regime for work outside the possession planning process could have increased the possibility of errors and omissions during the delivery of protection for work on track.
At the time of the incident, there was no requirement for this work to be notified to the Operations Division of Sydney Trains, so that some form of planning and preparation for the impact could have been made. At the time of this incident, Sydney Trains did not employ an integrated system to manage work on track in the rail network.
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