'''Principal arterials''' are the primary routes for traveling throughout the country, from one city to another, over long distances. Many principal arterials are freeways or expressways, but many others are not.
As a nationwide system, the [[wikipedia:United_States_Numbered_Highway_System|United States Numbered
Highway System]], often called '''U.S. Highways''', provides direct links between regions not served by the [[wikipedia:Interstate_Highway_System|Interstate Highway System]] , and as alternatives to travel on Interstates in the case of heavy traffic or incident.
*Roads in the '''United States Numbered Highways''' system (US Highways).
**This includes [[wikipedia:Alternate_route|alternate]] (ALT), [[wikipedia:Bypass_(road)#United_States|bypass]] (BYP), connector (CONN), truck, and scenic US Highways.
**This does ''not'' include
Business, Spur, and Loop US Highways.
*Business routes (Spurs and Loops) in the Interstate Highway System (e.g., I-69 Business Loop).