The NSW Supreme Court has questioned the legality of heavy vehicle signage, which may render unsafe past convictions for contravention of these signs.

Heavy vehicles are compelled by signage to enter heavy vehicle checking stations for assessment of their suitability to carry loads.

In defending their prosecution for failing to comply, the lawyers for two truck drivers argued that signage in the terms "Heavy Vehicle Checking Station 300m. Vehicles over 8t GVM must enter" did not strictly comply with the Road Rules and was confusing.

The judge agreed. He noted the definitions of vehicle, motor vehicle and truck under the rules had the combined effect that all trucks are vehicles, but only some vehicles are trucks (the rules define trucks as a motor vehicle over 4.5t GVM).

The judge also said that, by reason of those definitions, a sign requiring vehicles over 8t GVM to do something would necessarily include all trucks over 8t GVM but would not include all trucks.