IRP
The International Registration Plan, which apportions your plate fees across the states you run so one set of plates covers them all.
IRP is the International Registration Plan. It handles truck registration the same way IFTA handles fuel tax: instead of buying plates in every state you run, you register once in your base state and your fees get apportioned across the states based on how many miles you drive in each.
That is where the term “apportioned plates” comes from. When you register, you estimate or report your mileage by state, and each state gets its share of the registration fee. The cab card you carry lists every jurisdiction your plate is good in and the weight you are registered for.
IRP and IFTA go together but are not the same thing. IRP is about the registration and plates on the truck, IFTA is about the fuel tax on the miles. Both are reported by state, so keeping accurate mileage records feeds both.
Related: IFTA, USDOT number, operating authority.