State routes in Tennessee are divided into primary and secondary routes, the former being part of the federal-aid primary highway system, and the latter part of the federal-aid secondary highway system.

The route's number is displayed in small text at the bottom of each mile marker.

The Federal Aid Road Act of 1916 required states to establish a highway system in cooperation with the United States Secretary of Agriculture for the purpose of the distribution of federal highway funds.

Governor Austin Peay, who was elected in 1922, made road-building a central issue of his campaign.

[8] As automobile usage increased over the next several decades, additional routes were added to the system.

[10] A 1983 study conducted by TDOT also found that a number of important roads were partially maintained by both the state and local governments.

[11] To address this problem, in 1983 the Tennessee General Assembly signed legislation allowing the state to assume control of 3,300 miles (5,300 km) of city and county maintained roads, and made an additional 11,500 miles (18,500 km) of rural roads eligible for state aid.

[11][14] Secondary routes retained the original inverted triangle marker, with the "Tenn" removed.