The western terminus of the highway is at its intersection with SR 35 near Scottsboro.

SR 40 travels across the base of Lookout Mountain.

The narrow, twisty roadway continues until the highway reaches Dutton in western DeKalb County.

East of Dutton, the roadway has fewer curves as it continues across the county.

While SR 40 does not directly have an interchange with I-59, there is direct access to I-59 via SR 117 approximately 1 mile (1.6 km) southeast of the eastern terminus of the highway.