The toll fee paid by the motorist is calculated based on the entry point and the vehicle class, which is visually determined by the toll operator. In a fraudulent transaction, a delinquent operator may intentionally issue the wrong vehicle class. Thus, the consistency and accuracy of classification is crucial to the revenues generated by the toll system.

The Automatic Vehicle Classification (AVC) is a post-classification system. It uses the vehicle height and the number of axles to distinguish the different classes. As the vehicle leaves the toll lane, the classification is indepently determined by the AVC System. It verifies if the vehicle class keyed in by the operator matches that of the vehicle passing the toll lane. Any difference triggers the violation alarm to alert the attention of the toll supervisor.