Proposed features/lane transition

From OpenStreetMap Wiki
Jump to: navigation, search
Lane transitions
Status: Draft (under way)
Proposed by: xnyhps
Tagging: lane_transition=TBD
Drafted on: 2017-10-16

(Work in progress, the exact tagging scheme still needs to be worked out. I'm currently collecting examples to make sure the tagging scheme covers all of them.)

Proposal

Currently, highways can be tagged with how many lanes (lanes=*) they have and where those lanes are indicated to be going (turn:lanes=*). However, this information is not complete enough to follow a lane completely. If a lane appears without any turn indications, then the number of lanes increases but information about where exactly this lane is added is not present. It could appear on the left, on the right, and even in some cases somewhere in the middle. This proposal aims to add this data in a simple way that can be applied in a large portion of where lanes change.

Rationale

Navigation systems could show not only which lanes to take for the next exit, but also which lanes are optimal for what happens after that. To be able to do that, complete lane transition information is needed.

Proposed_features/transit already exists, however, it has a number of downsides:

  • The name is confusing, "transit" is often used in the context of public transport.
  • It proposes tagging the way to indicate the lane transition at the end of that way. This is confusing, and it makes it easy to break the tagging, for example by splitting a way.
  • It has no way to indicate that two lanes swap places, for example crossing a bus lane to enter a right turn lane.
  • It has not received many changes or discussion since the proposal was started in 2015, and is not being used very actively.

The goal of this proposal is to be used for tagging lane changes in the simple situation where the incoming and outgoing ways are clear. On an intersection there are often multiple possible combinations of incoming and outgoing ways, which means a relation would be needed, similar to restriction=*. This is currently not in scope of this proposal.

Examples

Currently out of scope:

  • An intersection where n lanes turn onto a road with m lanes with nm.

Tagging

TBD

Applies to

Nodes on two or more different highways for which the total lane count of incoming lanes does not match the total of outgoing lanes.

Rendering

If a render shows each lane separately, then it needs this proposal to fix the rendering at the points where the number of lanes changes.

Features/Pages affected

This would deprecate transit=*.

External discussions

Comments

Please comment on the discussion page.