Key:modifier

This key is used to indicate the designation that distinguishes a special route from its parent route. The modifier is typically identified by an auxiliary plate above or below a route marker. In an MUTCD-compliant country, such as the United States, a special route is identified by the combination of its network=*, ref=*, and modifier=*.

History

This key was part of the U.S. mapping community's original consensus about route relation tagging circa 2009, as seen on pages such as Interstate Highway relations:

• Distinct network=* tag for a route that has a shield distinct from its parent route, for example:
  • network=US:I versus network=US:I:Business
• modifier=* for a route that is signposted using the parent route's unchanged shield plus an auxiliary plate, for example:
  • modifier=* versus modifier=Business

Unfortunately, any data consumer that doesn't understand modifier=* would end up incorrectly handling some routes, such as by losing the distinction between a truck route and its parent route. This phenomenon is known as a "troll tag".

Over the years, modifier=* has remained in use but has become less important, as mappers have tended to always add to network=*, even when there is only an auxiliary plate and no distinction in the route shield. OsmAnd considers modifier=* to some extent when displaying shields,^[1] but most shield-capable renderers do not.^[2]

Other usage

modifier=left and modifier=right have also been used many times in an import of road_marking=solid_stop_lines in several U.S. cities. The meaning of these tags is unclear, but it is probably a nonstandard way to indicate the side of the road.

See also

• MUTCD Series M

References