Vehicle classification by weight and design determines definitions and regulatory categories for passenger and goods vehicles. The statute provides operative definitions and classification criteria for motor vehicles by design, use and weight: goods carriage (vehicles constructed or adopted for carriage of goods or so used), gross vehicle weight (registered total permissible vehicle plus load), and unladen weight (vehicle weight with ordinary equipment excluding driver). It identifies vehicle classes-heavy, medium and light passenger vehicles, medium goods vehicles-and defines tractor as a non-load-carrying motor vehicle excluding road-rollers.