The rural principal arterial system consists of a connected rural network of continuous routes having the following characteristics:

(1) Highways having high density of intrastate and interstate travel.

(2) Highways that serve urbanized areas and a large majority of small urban areas. The rural principal arterial system may serve an urban area if the system either penetrates the urban boundary or comes within 10 miles.

(3) Provide an integrated network without stub connections except where unusual geographic or traffic flow conditions dictate otherwise.

The principal arterial system is classified into the following two subsystems:

Interstate System: All designated Interstate routes.

Other Principal Arterials: All non-Interstate principal arterial highways.