The following description was taken from MUARC: Guidelines for Vehicle Safety Markings for Fleet Vehicles :

Transurban has identified a need for vehicle safety markings guidelines for road operators and infrastructure builders in the transport sector. It is anticipated that these guidelines would apply primarily to: (1) incident response, (2) project site vehicles and (3) sweepers, tow trucks, etc.

The main criteria for vehicle safety markings on incident response vehicles should be to ensure the safety of both vehicle operators and the general public. This should be achieved through being highly visible during daytime and at night and, to a lesser extent, as a vehicle owned or operated by a particular company or organisation. For vehicles not specifically operating as emergency response vehicles, the listed criteria are most important when stationary at the roadside rather than with the goal of warning road users while in motion.