Define “own weight”:

1. Correct answer: The vehicle’s weight including all accessories plus fuel, water and oil, excluding driver and freight.
2. The vehicle’s weight with freight and with the driver, including the weight of the all accessories plus fuel.
3. The vehicle’s volume including all accessories plus fuel, water and oil, excluding driver and freight.
4. The vehicle’s weight including all accessories plus fuel, water and oil, including driver and freight.

WhyOwn weight is the vehicle with all its accessories, fuel, water and oil, but without the driver and freight. Volume has nothing to do with it.