From OpenStreetMap Wiki
|National Highway System|
|Used on these elements|
|Tools for this tag|
Several countries have a defined National Highway System network that is independent of numbered routes. The tag is currently used in the United States and Canada.
- NHS=yes - normal value to indicate that the road is on the NHS, and is not an Interstate or STRAHNET route in the U.S.
United States subsets
- NHS=STRAHNET - Describes non-interstate STRAHNET routes, representing the most important non-Interstate NHS corridors.
- NHS=STRAHNET_(connector) - A connector road from a STRAHNET route to a military installation or port.
- NHS=Interstate - Used on Interstate highways.
- NHS=Intermodal - Intermodal connectors.
- NHS=Intermodal;STRAHNET_(connector) - Technically a two-value key but considered its own NHS subset.
- NHS=MAP-21 - A MAP-21 Principal Arterial.