Federal-aid highway program

• The Interstate Highway System
• The Federal-aid primary highway system is a system of connected main highways, selected by each state highway department subject to the approval of the Bureau of Public Roads. It encompasses routes of the Interstate System and other important routes serving essentially through traffic with their urban extensions, including important loops, belt highways, and spurs.
• The Federal-aid secondary highway system consists of the principal secondary and feeder routes including farm-to-market roads, rural mail and public school bus routes, local rural roads, county and township roads, roads of the county, road class, and their urban extensions. These roads are chosen by the state highway departments and appropriate local road officials cooperatively, subject to approval by the Bureau of Public Roads.