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Mineral Mines & Quarries Inspectorate | Bulletin | No.219 V 1 | 22 April 2024

Tow Hitch Failures

What happened?

In a 14-month period, there have been eight High Potential Incidents relating to tow hitches. Trailers detaching while in motion present a significant hazard to persons on mine sites.

Incident DateIncident DescriptionFailure MechanismPrimary Causes
21/2/24A loaded truck and dog was travelling between mines on public roads when the trailer separated.A-frame drawbar structure failed behind the hitch.Fatigue loading failure.
11/2/24A loaded B double travelling on a site haul road - rear trailer has separated.Bolt-in drawbar eye sheared.Fatigue loading failure.
13/12/23Light vehicle towing a fuel trailer along a site road - trailer has separated.Tow hitch insert sheared - safety chains not attached.Tow hitch underrated for duties.
10/12/23A loaded quad road train was travelling on a regional road. Three trailers have separated.Bolt-in drawbar towing eye failed at thread.Lock pin / bolt for the castellated nut sheared.
20/7/23Light vehicle towing a dual axle trailer - trailer has separated from the tow vehicle.Detached from tow ball - safety chains not connected. Coupling not fastened securely during latching.
18/4/23After proceeding through a boom gate, the rear trailer of a chemical delivery road train has separated.Trailer kingpin uncoupled at turntable.Coupling not fastened securely during latching.
7/4/23A loaded triple road train was travelling on a haul road when the third trailer has separated.Bolt-in drawbar eye sheared. Fatigue loading failure.
14/1/23Loaded road train travelling on a haul road. The second trailer has separated.Bolt-in drawbar towing eye has sheared.Fatigue loading failure.

Key issues

The hitch arrangements for road trailer are often a high stress point and tend to fail in situ if operation and maintenance processes are not effective at maintaining a healthy hitch.

  • Operation of on-road trucks in a mining environment can often result in increased wear and tear on equipment such as couplings due to harsh conditions, higher loading, and road construction different from that typically seen on public roads. Maintenance strategies must ensure this is taken into account. Inspection and maintenance frequency often needs to be increased.
  • Signs of wear and premature failure of couplings, towing eyes, and drawbars can be detected visually or through the use of measuring equipment such as 'go, no-go' gauges available from coupling manufacturers and third-parties.
  • Appropriate knowledge / information on sites regarding standards applicable to on-road trucks and haulage.


The hitch point is a safety-critical component. Consider if hitch arrangements on site are designed, operated, and maintained in a manner which reflects the operating environment with specific focus on:

Design: Appropriately robust and durable for the operating conditions, subjected loads, and life of product.

Operate: Vehicle speeds, acceleration, braking, cornering rates, road surfaces, safety chains / devices in place. Wet weather considerations, slopes / grades, QA for coupling / uncoupling activities.

Maintain: Lubrication, cleaning, inspection regime. Replacement of high stress components as a suitable frequency, assembly methods, QA of functions, tensioning, and corrosion management.

References and further information

NHVR – Vehicle Standard Guide 4 (VSG4)

NHVR – Vehicle Standard Guide 31

Heavy Vehicle (Vehicle Standards) National Regulation

Vehicle Standards Bulletin 6.

National Heavy Vehicle Inspection Manual

Authorised by Hermann Fasching - Chief Inspector – Mineral Mines & Quarries

Contact: Mark Genge, Inspector of Mines - Mechanical

Issued by Resources Safety & Health Queensland

Safety: This information is issued to promote safety through experience. It is not to be taken as a statement of law and must not be construed to waive or modify any legal obligation.
Placement: Place this announcement on noticeboards and ensure all relevant people in your organisation receive a copy, understand the content, findings and recommendations as applicable to their operation. SSEs should validate that recommendations have been implemented.