Thursday, September 10, 2026

Safety Message: Automatic Park Brakes

Following recent technical assessments, ONRSR would like to highlight the risk of runaway movements on the network due to the unsafe release of Automatic Park Brakes (APBs) on freight wagons.

Rail transport operators are advised that while the train air brake system is failsafe, because the brakes apply when a higher brake pipe pressure is exhausted to atmosphere due to the pressure gradient, the application will not hold indefinitely. This is because air pressure in the reservoirs and brake cylinders on wagons leak off over time. Subsequently, mechanical handbrakes must be applied for holding rolling stock stationery for longer periods of time.

Handbrakes are also used to prevent runaway while the brake pipe air pressure is recharged after stopping trains on gradients. Conventional handbrakes on freight wagons require manual operation of a mechanical device to apply and release braking force through the rigging to the wheels. Only manual operation of the mechanical device on each wagon releases or applies the handbrake force on that wagon.

APBs are being installed on freight wagons in Australia in increasing numbers. As a result ONRSR is highlighting:

a) the risk of runaway movements that could arise in yards, terminals, sidings and on mainline gradients due to unintended release of APBs.

b) controls that rolling stock operators should implement to mitigate this risk.

Background

Unlike conventional handbrakes, APBs use brake pipe pressure reduction to operate a mechanical device that locks the piston in the applied (extended) position. The mechanism does not move the piston to the applied position but only locks it in that position once cylinder pressure has moved it. For the brakes to release, the mechanical device must be unlocked by recharging brake pipe pressure. All applied APBs on the train are released when the brake pipe pressure is recharged, except for APBs where a hold valve has been activated.

While APBs have significant benefits, including not requiring crews to apply handbrakes manually to secure trains, the way in which they apply and release can present risks to rail safety.

Firstly, if a wagon has air brakes cutout (ACO) the APB will not move the piston and rigging into the applied position, leaving the ACO wagon unbraked. As such, APBs are regarded as supplementary safety devices to conventional handbrakes.

Secondly, if train crews accustomed to manual handbrakes use APBs, they might expect mechanical brakes will still be applied when the brake pipe is being recharged. This could result in an unintentional release of all brakes on the train, resulting in runaways on gradients.

Action Required

To mitigate these risks, rolling stock operators should:

Ensure change management and risk management around APB introduction has fully identified and controlled all hazards, including those associated with engineering design, construction, operation and maintenance of APBs.
Ensure freight wagons are not commissioned or operated with APBs as the only holding brake system.
Update and refresh training and procedures to support crew and maintenance staff competency in safe APB operation, including when to activate hold valves and/or apply handbrakes.
Ensure that it has been brought to crews’ awareness that:
- APBs do not apply on ACO wagons because they do not move the brake piston and rigging into the applied state. Conventional handbrakes must be applied when ACO wagons are to be secured.
- When a train is stopped on a gradient and APBs are applied, hold valves must be activated on the required number of APBs before recharging the brake pipe.
Update and refresh training and procedures for train crews on the importance of applying the brakes before detaching wagons fitted with APBs from trains.
Place adequate emphasis on critical procedural controls to signify their importance and ensure that crews who are required to implement these procedural controls clearly understand why the specified actions are required. Critical procedures communicate safety-critical tasks that must be fully actioned by crews responding to atypical or unexpected situations. Crews must therefore ensure they take sufficient time to methodically perform and verify the effectiveness of each required action.

Related Resources

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