Proposal:Gantry Expansion

Gantry Expansion
Proposal status:	Draft (under way)
Proposed by:	SherbetS
Tagging:	Data item
Statistics:
Draft started:	2026-09-04

Problem Statement

Presently, the documented guidelines on the wiki have two top level tags that are recommended to be used for tagging a gantry, highway=toll_gantry man_made=gantry. This is confusing because seemingly the same feature has two different keys and two different ways to represent the same object. highway=toll_gantry was the result of a proposal that was written without considering uses for a gantry other than tolls, while man_made=gantry stemmed from an abandoned proposal due to demand for a tag to represent the generic gantry, an extremely common feature. It mentions in passing some undocumented keys that mappers have used to try and describe what the gantry is being used for, but there does not exist a clear documented way to represent how the gantry is being used.

Additionally, the archived proposal for man_made=gantry suggests that each node on the gantry represents a support, but this makes no sense in the case of a gantry that hangs on one side, or one where nodes are being used to represent some object mounted to the gantry, such as a variable message sign or camera.

As such, the documentation for both tags is somewhat half baked, contradictory, and not very useful in providing a clear scheme to represent all kinds of gantry. This proposal aims to remedy the problems by establishing a sensible and unified tagging scheme that can richly represent the variety of different gantries that exist in the real world.

Proposal

I propose:

1. Establish a new namespace, gantry:*=* to be used in combination with man_made=gantry
2. Under the new namespace, add the key gantry:construction=* to specify if the gantry construction is lattice, tube, girder, or other values. This mirrors how tower:construction=* is used to describe towers and masts.
3. Under the new namespace, add the key gantry:structure=* to describe the support design of the gantry.
4. Under the new namespace, establish a new namespace, gantry:use:*=*. This can be used to describe all the uses of the gantry, and can be used to describe gantries that fit into more than one use category (ex: a gantry with a variable message sign and toll cameras). This mirrors how service:vehicle:*=* is used to describe the different services that a shop=car_repair provides.
5. Establish that each node in a way representing a gantry does NOT represent a support, unless it is explicitly tagged with a support=* value.
6. Establish the default value layer=1 for all gantries, and document that layer should be one greater than the road the gantry overhangs.
7. Deprecate highway=toll_gantry in favor of man_made=gantry + gantry:use:toll=yes

Rationale

Rationale

• The new scheme will provide an appropriate and easy to query alternative to highway=toll_gantry, while unifying it with man_made=gantry. This would address concerns that were brought up in the original proposal.
• The new scheme will provide a documented way to tag the construction and use of the gantry in a way that is easy to query, without using semicolons.
• The new scheme will provide a way to represent the supports of the gantry, while also allowing other features to be conceptually attached to the gantry, as well as leaving room to tag gantries that are only supported on one side.
• The new scheme will be flexible to how much detail the mapper chooses to add, just specify that a gantry exists, optionally specifying what is on the gantry, how the gantry is constructed, and what the gantry is used for.

Comments

Please comment on the discussion page.