International Registration Plan (IRP)

An agreement that provides for the apportioned registration of commercial motor vehicles based on the total miles traveled in each jurisdiction. The IRP has emerged as the proration agreement mandated by the federal government under the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991. All U.S. states except Alaska and Hawaii were required to become a member of the IRP by September 30, 1996, or forfeit their right to assess vehicle registration fees for interstate motor carriers registered in other states.