Individual states are encouraged to focus federal funds on improving the efficiency and safety of this network.

The Intermodal Surface Transportation Efficiency Act (ISTEA) in 1991 established certain key routes such as the Interstate Highway System, be included.

The legislation designated about 160,955 miles (259,032 km) of roads, including the Interstate Highway System, as the NHS.

Aside from designating the system, the act served several other purposes, including restoring $5.4 billion in funding to state highway departments, giving Congress the power to prioritize highway system projects, repealing all federal speed limit controls, and prohibits the federal government from requiring states to use federal-aid highway funds to convert existing signs or purchase new signs with metric units.

[9] This article incorporates public domain material from websites or documents of the United States Department of Transportation.