What it means
A FASTag reader at the lane reads the tag's identity by radio. The toll system then deducts the fee from the prepaid wallet or bank account linked to that tag. Because the tag identifies the account, not the plate, a tag moved to another vehicle or a tag with no balance creates a mismatch that only a camera can catch.
How it applies in India
According to IHMCL's FAQ, FASTag uses RFID, is fixed on the windscreen, and is issued by banks that IHMCL has certified, with an NHAI FASTag variant that can be linked to a bank account through the My FASTag app. IHMCL (Indian Highways Management Company Limited) is the company set up with equity from NHAI, concessionaires and financial institutions to implement electronic toll collection on national highways. In MLFF tolling, FASTag works together with ANPR: the tag pays, and the plate read identifies vehicles whose tag fails. At lane plazas, ANPR and ATCC also check that the vehicle class charged matches the vehicle.