Thursday, May 27, 2021

Safety Message: 'A1 SPADs’ – Limit of authority missed by train crew

Note: As a result of the National Rail Safety Data Strategy implementation, from 1 July 2022, A1 SPADs are Category A Proceed Authority Exceedances. Further information about reporting and occurrence data submission requirements can be found here

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ONRSR is reminding rail transport operators about a range of risks, causes and controls associated with A1 SPADs

A Signal Passed at Danger (SPAD) is where rolling stock passes a stop indication / aspect or exceeds the limits of authorised movement without authority. As per ONRSR’s Reporting Requirements for Notifiable Occurrences, an ‘A1 SPAD’ is “When a SPAD has occurred and, according to available evidence, a stop aspect, indication or end of movement authority was displayed or given correctly and in sufficient time for the train to be stopped safely at it.”

Such incidents can result in injuries or fatalities, especially where the A1 SPAD leads to a derailment or collision with another train (see the Safety Message: Train to train collision). While ONRSR’s investigations into A1 SPADs have identified several causes and contributing factors, there are also several mitigations that can minimise the risks. While not exhaustive, given the range of operational environments within the Australian rail industry, the following causes/contributing factors and controls should be noted.


  1. Individual factors
    • e.g. driver fatigue, distractions, miscommunication, workload, read through/read across errors, distraction, error due to driver expectancy and habituation.
  2. Organisational factors
    • e.g. inadequate controls, use of inadequate controls, inadequate maintenance, procedures, rules, training, culture, leadership.
  3. Technological or equipment factors
    • e.g. poor signal placement such as inadequate lateral, vertical or horizontal placement, signal spacing too close, poor signal design leading to confusion, signals sighting blocked by obstructions.
  4. Environmental factors
    • e.g. poor visibility, trees blocking signals, non-light signals near the rail corridor causing misinterpretation or distraction.


While not an exhaustive list, ONRSR is aware of the following controls that are available and have been used in railways both in Australia and overseas. rail transport operators (RTO) should note that there are safety and operational benefits and detriments associated with each control. Operators must consider a range of factors, including the likelihood of the hazard and the degree of harm to determine what controls are reasonably practicable to implement – see the ONRSR Guideline – Meaning of duty to ensure safety so far as is reasonably practicable SFAIRP for more information.


The main types of engineering controls include signalling and train protection systems such as:

  • driverless systems that eliminate the need for a driver and thus the risk of A1 SPADs.
  • in-cab signalling systems displaying signal aspects in the driver cab eliminating many of the risks associated with visibility of signals.
  • fixed block colour light signalling systems - with enforcement - ensure that if an A1 SPAD does occur, it will not result in a collision with another train.
  • Proximity alerts to the driver of the prevailing limit of authority as a reminder not to proceed beyond that point without further authority.


Organisational controls include:

  • Implementing effective operational and engineering SPAD investigation, monitoring and analysis, as well as SPAD committees, to identify, assess, control and review signals with higher SPAD risk and / or event history.
  • Implementing signal sighting systems, processes and procedures to appropriately identify the most suitable position for new or relocated signals e.g. documented procedures, checklists, sighting committees (consisting of appropriately trained and competent engineering, design, operational and train crew reps), post installation site review, applicable RIM / Rolling Stock Operator sign off and approvals.
  • Train orders, special proceed authorities, condition affecting network (CAN) forms and warnings, and other driver communications that are clear, succinct and easy-to-understand.
  • Driver training including use of simulators, learning from experienced drivers and recertification processes to ensure drivers understand signals on their route and demonstrate competent train handling on those routes.
  • SPAD alarms and improved network control centre displays so that signallers are aware when a SPAD has occurred and can intervene accordingly.
  • Rail Resource Management implemented to help drivers maintain effective non-technical skills such as communication, situation awareness, and organisational processes to manage fatigue.

Lineside/wayside signal controls include:

  • Design of signals and indications to minimise the risk of driver error through:
    • LED signals providing increased visibility and improved reliability over incandescent lamps.
    • Repeaters assisting drivers at locations with limited signal sighting distance.
    • Co-acting signals assisting drivers if the signal becomes unsighted or to make the indication. easier to see, such as on a curve or when stopped at a platform.
    • Masts and gantries positioning signals to minimise read across errors on adjacent tracks.
    • Consistent positioning of signals on the same side of the running line.
  • Signal backgrounds to make signals easier to see through:
    • Maintenance / use of backboards to increase contrast against visual background and clutter
    • Use of signal hoods make signal aspects easier to see in sun glare.
  • Signal placement to assist the driver see the signal through:
    • laterally closing to the track at a similar height to the driver in the cab, so the signal is within the driver’s field-of-view
    • clearance of obstructions
  • Maintenance of signals such as removing vegetation, or non-signal lights near the rail corridor, and maintaining the signal itself.

Rolling stock controls minimise distraction and help position the driver to sight signals through:

  • Displays, alerts and radios that are ergonomically designed to provide key information to the driver but minimise distraction
  • Seat design and placement that is adjustable so drivers of different sizes can see the signal while seated.
  • Sun glare is managed by, for example, undertaking a ‘glare study’ to design the driver’s cab to account for the risk of sun glare (such as use of blinds and window tinting) or ensuring the windscreen (using wipers or regular cleaning) is clear.
  • Ensuring rolling stock is well maintained, particularly the braking systems are operating to optimal performance.

A comprehensive collection of ONRSR Safety Messages is available to view here.

Last updated: Jan 11, 2023, 11:59:26 AM