Interstate ports of entry have to do with the regulation of commercial highway traffic. Here's an explanation by the State of Arizona:
Arizona operates 22 fixed Ports of Entry throughout the state, in addition to the main Commercial Permits office. Six of the ports are international border ports.
The mission of the Port of Entry program is to ensure that all commercial vehicles operating on Arizona highways are properly credentialed, and in safe operating condition while providing efficient, fair, and friendly treatment to all of our customers and citizens of the State of Arizona.
Arizona Ports of Entry monitor and screen all commercial traffic entering the State of Arizona for registration, motor tax, size and weight restrictions, commercial drivers license requirements, insurance requirements, and motor carrier equipment safety requirements.http://www.azdot.gov/MVD/commercialenforcemen...