I-10 connects Santa Monica, California to Jacksonville, Florida, extending between the Pacific and Atlantic oceans).

Five route numbers are duplicated in the system; the corresponding highways are in different regions, reducing potential confusion.

In addition to the 48 contiguous states, Interstate Highways are found in Hawaii, Alaska, and Puerto Rico.

However, these routes are not required to meet the same standards as the mainland routes: Highways on the Interstate System in Alaska and Puerto Rico shall be designed in accordance with such geometric and construction standards as are adequate for current and probable future traffic demands and the needs of the locality of the highway.

They are fully controlled-access routes built to the same standards as the mainland Interstate Highways.