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Public-images-osm logo.svg network = US:TN
Tennessee 155.svg
Tennessee primary and secondary state routes in the U.S. state of Tennessee. Edit or translate this description.
Group: Properties
Used on these elements
should not be used on nodesshould not be used on waysshould not be used on areasmay be used on relations
Useful combination
Status: de facto

Distinguishing primary and secondary routes

A given Tennessee state route may have two completely different shields along different segments of the route:

A single route relation's ways can alternate many times between the two shields, based on the state's official highway functional classification for roads along the route. This classification does not necessarily match the criteria that mappers normally use to choose highway=* tags in OpenStreetMap. Occasionally, a driver may approach a junction where they have to choose between the primary and secondary legs of the same route – signs bear the same number on two different shapes. [1]

Historically, mappers have taken two different approaches to distinguishing between the two shields:

  • Tagging ways along primary routes as highway=motorway/trunk/primary and tagging ways along secondary routes as highway=secondary/tertiary, regardless of the usual criteria for highway=* tagging.
  • Tagging ways along primary routes as ref=TN * and tagging ways along secondary routes as ref=SR *, even though in reality Tennesseans always use "SR" for both kinds of routes.

Out-of-state mappers have muddled both approaches over the years due to a lack of awareness about the dual route signage system, so data consumers currently have no way to reliably choose the right shield.