interstate

Interstate is an adjective and noun used to describe things that involve or connect two or more states. It is commonly applied in geography, law, transportation, and politics to indicate cross-border or multi-state connections and activities.

In the United States, the term is most closely associated with the Interstate Highway System, a nationwide network of controlled-access highways designed for high-speed travel and freight. Authorized by the Federal-Aid Highway Act of 1956, the system links major urban centers and regions to support interstate commerce and mobility. The network uses a standardized numbering scheme, with primary interstates designated by one- or two-digit numbers and ancillary routes by three-digit numbers.

Interstate matters also arise in law. The concept of interstate commerce, regulated by Congress under the Commerce Clause of the U.S. Constitution, covers activities that cross state lines, such as the shipment of goods or the movement of people, and has shaped federal authority over many economic and transportation activities. This framework distinguishes interstate actions from intrastate ones, which occur within a single state.

Interstate compacts are formal agreements between two or more states, authorized by the Constitution to address common problems, coordinate policies, or manage shared resources across borders. Such compacts require permission from Congress in many cases and represent a cooperative approach to cross-border governance.

Outside the United States, the term is used more generally to describe cross-border connections between states or subdivisions, though the exact legal and administrative structures vary by country.