Which classification of roadways typically carries 90% of traffic volume in the US?

The classification of roadways that typically carries 90% of traffic volume in the US is the principal arterial. Principal arterials serve as the major highways that facilitate long-distance travel between cities and major hubs, connecting various regions. These roads are designed to carry large volumes of traffic and provide significant connectivity, making them essential for both local and interstate transportation.

In contrast, other classifications such as minor arterials, collectors, and local roads have different traffic roles. Minor arterials serve as connections to the principal arterials and provide less capacity and longer distances between intersections. Collectors gather traffic from local roads and funnel it to minor and principal arterials, while local roads primarily serve residential areas and have lower traffic volumes. Understanding this hierarchy of roadway classifications helps in grasping how traffic is managed across various types of streets and highways.