Proposal:Traffic mirror relation using ways

Traffic mirror relation using ways
Proposal status:	Draft (under way)
Proposed by:	Biff
Tagging:	type=traffic_mirror Data item
Statistics:
Draft started:	2025-03-04

Proposal

This proposal suggests introducing a relation similar to the one already specified in highway=traffic_mirror - however using ways as "from" and "to" members of the relation, quite similar to how a relation is used for mapping of a turn restriction.

Rationale

Currently, highway=traffic_mirror specifies two options for tagging of traffic mirrors:

1. Simply tagging the node where the mirror is located with highway=traffic_mirror. This provides no info about how the mirror is intended to be used. Sometimes, taggers have used direction=* to provide information about the direction in which the mirror is facing. However, a navigation would have to do rather complex calculations to find out if the mirror is relevant for a driver.
2. Using a relation of type=traffic_mirror with three nodes of the types "from", "to" and "mirror". This does provide info about how the mirror is intended to be used. However, using nodes as members for the relation does not appear to make sense to me, as an exact "from" node is not always easy to identify and the visibility of the "to" street depends on many factors like the height of the driver's eyes above the road surface. Typically, the driver will not only see a single "to" node in the mirror but a larger section of the "to" street.

Tagging

Tags

The relation is tagged as follows:

Key	Value	Comment	Presence
type	traffic_mirror	Defines this relation as a traffic mirror relation.	! Required

Members

Role	Refers to	Comment	Presence
mirror	node tagged with highway=traffic_mirror	Node at the position of a mirror. Typically, one traffic mirror relation can have only one "mirror" member.	! Required
from	way or node	The way or node from where the user (driver) can see the mirror. If a way is used, it does not need to be limited to a specific section of the "from" street. If a node is used, then it should be in the place where the user (driver) typically stops and should be a node on the "from" street. Typically, a traffic mirror relation can have only one "from" member.	! Required
to	way (or node)	The way (or node) that the user (driver) sees when using the mirror. If a way is used, then it does not need to be limited to a specific section of the "to" street. Using a node is permitted for compatibility with the old traffic mirror relation that only uses nodes. The relation can have several "to" members, if more than one "to" street can be seen from the "from" way or node.	! Required
via	node where the "from" and "to" streets meet	Similar to the "via" point of a turn restriction.	? Optional

Examples

Simple example

For a simple example, see the relation https://www.openstreetmap.org/relation/18783095

Where the pole with the mirror is located on the sidewalk, a node was placed with the tag highway=traffic_mirror (and also with the optional tag direction=*).

A relation "type=traffic_mirror" was created with the following members:

1. "mirror": The mirror node.
2. "from": The street from where the mirror is typically seen.
3. "to": the part of the street that is seen through the mirror.

Advanced example

For an advanced example, see [1]. In this example, two mirrors (for looking left and right) are located opposite the exit of a supermarket's parking lot.

Tagging is as follows: Node tagged with "highway=traffic_mirror" where a pole with the mirrors is located on the sidewalk, opposite the exit lane of the supermarket. Relation "type=traffic_mirror" with the members: # The mirror node as "mirror",

1. the exit lane of the supermarket as "from",
2. the part of the street left from the intersection with the exit lane as "to", and
3. also the part of the street right from the intersection with the exit lane as "to".

A map should show the node tagged with "highway=traffic_mirror".

A navigation system would know that the driver intents to leave the parking lot via the "from" way or the "from" node and is going to turn right (or left) to a "to" way or through a "to" node. It would then make the driver aware of the traffic mirror on the other side of the street.

Rendering

Rendering of the relation probably does not make sense.

However, a navigation system could make the driver aware of the location of a mirror that is helpful to safely see traffic on the intended route (when "from" and "to" align with the route of the vehicle).

Features/Pages affected

highway=traffic_mirror needs to be edited if the proposal is approved.

External discussions

The idea for this proposal started on Talk:Tag:highway=traffic mirror.

Comments

Please comment on the discussion page.