The National Highway System (NHS) is a network of roads important to the nation's economy, defense, and mobility. The NHS consists of the Interstate System, highways functionally classed as freeways and expressways, other principal arterials, roads important to national defense, plus intermodal connectors. Intermodal connectors link intermodal terminals to the remainder of the NHS. The NHS was developed by the US Department of Transportation in cooperation with the states, local officials, and metropolitan planning organizations, including CMAP.
A map was prepared in the fall of 2018 to reflect 2018 changes in the National Highway System. This map is posted here: National Highway System for the Chicago Region, September 2018
The NHS has gained increasing importance recently, since it is now the basis of federal highway asset management regulations and many transportation system performance measures and targets. Some federal regulations, including design standards and billboard regulations, continue to apply to the NHS.