Apportioned vehicles must be registered under IRP. The term apportioned means a “prorated” registration program that allows payment of license fees based on the total distance operated in two or more member jurisdictions, these jurisdictions are the 48 states of US (Canada and Mexico are included also in certain circumstances). All jurisdictions have agreed to allow one jurisdiction (base jurisdiction) to collect the license fees due. The base jurisdiction calculates and collects the license fees due to all member jurisdictions in which the registrant’s fleet/vehicles will be operated. The fees are divided and disbursed periodically. So if your tractor traile operates in all 48 states, the the fees paid will be disbursed to all 48 states.