Over Size Over Mass Unit

The Over Size Over Mass (OSOM) Unit has been established in consultation with the transport and logistics industry, to facilitate the smooth running of operations involving OSOM loads throughout WA. OSOM loads are large indivisible items, special purpose vehicles (i.e. cranes) or agricultural machines or implements. 

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The OSOM Unit’s primary purpose is to provide the transport industry with a ‘one stop shop’ for all of their logistical needs involving OSOM movements.

In addition to issuing permits, the Unit also coordinates bookings for traffic escort services (a function previously held by WA Police), and in the future will work with both Western Power and Horizon Power to coordinate bookings where power line lifting is required. 



To move an OSOM load, transport operators require either a Single Trip Permit or an Over Size Over Mass Permit.

Single Trip Permits are issued to move loads that are large indivisible items such as modules or mining equipment, and are valid for a single move.  These loads are usually travelling from a metropolitan manufacturing centre to a resources sector site, often located regionally.  Due to the oversize dimensions, a traffic escort and a pilot vehicle/s are usually required.  Due to their size, these moves often require night time rolling road blocks to assist in the movement of the load.

Class 1 Permits are issued for a period of either 12 or 36 months. These permits are generally issued to a towing vehicle in combination with a single trailer, or to special purpose vehicles such as mobile cranes. These permits have defined limits (mass, width, length) which are outside the vehicle standard regulations, and are allowed access to a predetermined network of roads. Period Permit holders must adhere to specific operating conditions, for example hours of travel and appropriate warning lights. 


Night Moves

Recently, there has been a marked increase in the number of applications received for OSOM permits. In an effort to reduce the impact on road users, Main Roads have introduced night moves in the Perth metropolitan area and in the Pilbara region. This will aim to reduce the number of OSOM loads on the road network during peak travel times, while ensuring safety and reducing the impact on all road users. Further information about night moves is provided in HVO Update 53-2012.

Modified: 26 Jul 2014