The Idaho Transportation Department (ITD) is responsible for the establishment and classification of a state highway network, including 5,000 mi of roads that are classified as Interstate Highways, U.S. Highways, and state highways within the state of Idaho in the United States. The current state highway marker consists of a white background, black numbering, and a solid black geographic outline of the state of Idaho.

History

During the 1920s, in lieu of numbering its highways, Idaho had a system of lettered Sampson Trails. They were marked by businessman Charles B. Sampson of Boise at no expense to the state, using orange-colored shields. By 1929, the trails system had included 6,500 mi of marked highways that covered most of the state. By the mid-1930s, the state had adopted a more standard system of numbered state highways. In 1978, the ITD began using brown state highway markers to denote scenic Idaho highways, in addition to the main highway markers that featured a black background and white lettering and the name "IDAHO" in black lettering inside a white geographic outline of the state. The brown markers were discontinued around 2012, and in April 2020, ITD changed the coloring of the main state highway marker to its current color scheme, also adding a wide version of the marker for three-digit highways and removing the word "IDAHO" from all markers in the process.

Sampson Trails

The following Sampson Trails were marked:

State highways