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The National Highway System Designation Act of 1995 was signed by President Clinton on November 28, 1995. This act designates 160,955 miles of roadways as the National Highway System (NHS) including 2,897 miles in Indiana. The system includes the Interstate Highway System as well as other roads important to the nation’s economy, defense, and mobility. The NHS was developed by the United States Department of Transportation in cooperation with the States Departments of Transportation, Local Officials, and Metropolitan Planning Organizations. Included in the national system is a identification of major intermodal terminals (rail-truck terminals, maritime ports, airports, and intermodal passenger facilities) and the highways that provide connections between these intermodal facilities and the NHS. The NHS and the additional intermodal connector routes provides an integrated transportation system to support the nation’s economy. As stated by the President, "The designation of the National Highway System makes clear that transportation should be viewed as a single system with each mode complementing the others. Manufactures and shippers rely upon several modes of transportation to deliver their products to consumers in the most efficient manner possible. The National Highway System unites these different modes by providing access to major ports, airports, rail stations, and public transit facilities."
The National Highway System includes the following subsystems of roadways (note that a specific highway route may be on more than one subsystem):
- Interstate: The current Interstate system of highways retains its separate identity within the NHS.
- Other Principal Arterials: These are highways in rural and urban areas which provide access between an arterial and a major port, airport, public transportation facility, or other intermodal transportation facility.
- Strategic Highway Network: This is a network of highways which are important to the United States’ strategic defense policy and which provide defense access, continuity and emergency capabilities for defense purposes.
- Major Strategic Highway Network Connectors: These are highways which provide access between major military installations and highways which are part of the Strategic Highway Network.
- Intermodal Connectors: These highways provide access between major intermodal facilities and the other four subsystems making up the National Highway System.
The National Highway System and its role in determining geometric design of highways is discussed in Section 40-1.03 (01) of Chapter 40 "Basic Design Controls" of the Indiana Department of Transportation’s Design Manual.