Proposal:Median strip

Median strip
Proposal status:	Draft (under way)
Proposed by:	ManuelB701
Tagging:	median=* Data item
Applies to:	way
Definition:	Denotes the existence of a physically accessible area of a carriageway in the middle of the road but is not set as a driving lane.
Statistics:
Draft started:	2025-02-12

Proposal

The purpose of this proposal is to map a highway's flush median strip (also known as the central reservation and central media). It's added to a highway=* where the middle of a road is legally forbidden but still physically accessible (basically an inaccessible lane).

Rationale

The closest feature to map medians is with the use of divider=*. The feature has been proposed as divider=area but has been abandoned. Beyond that, divider=median has been established but was never documented and the current documentation only uses divider=* as a linear feature instead.

Beyond that, some mappers also have used access:both_ways=no but medians aren't proper lanes in that they aren't meant to be driven over and can easily confuse data consumers with actual lanes.

Using *:median=* makes it pretty clear that there is a strip in which drivers shouldn't drive over. In relation to divider, I'm of the opinion that tagging medians with their own key is more useful for data consumers and differentiates between 2D and 3D features.

Tagging

A "new"<ref>It actually has nearly 12000 uses, even surpassing divider=* alone.<ref> key is introduced, median. Possible values include

• no - there is no median on the road (the default value, according to taginfo, this is the most common use)
• yes - there is some median on the road
• stripes - the median has the same surface as the rest of the highway but is marked with painted stripes
• surface - the median has a different surface of the carriageway, may be optionally separated by (flush) kerbs

To describe the median more in detail, *:median=* is introduced functions similar to *:lanes=*. This means, attributes like width, surface (for median=surface) or embedded_rails (in case the trackbed is not separated by barriers but still visibly marked) can be used to set the median's properties, though others like access:lanes are invalid because they are not meant to be driven on.

It can also be combined with the placement=* tagging. Here, the median replaces the lane number. So in order to tell that the way follows e.g. the middle of the median strip, you'd use placement=middle_of:median (note that the direction is omitted because medians are by definition in the middle of the road and entering a direction is therefore unnecessary). For placement=transition, median=yes can be used to easily tell data consumers that a lane grows in the middle of the road and not at its edge.

For changes in surface, can be used to denote the existence of kerbs. Note that at a certain kerb height, the road should be drawn as two ways instead.

The tag should not be used on physically undriveable (e.g. because the surface is made of grass or gravel), inaccessible (i.e. a barrier such as guard rails, raised kerbs or row of trees exists between both lanes) or very wide (since mapping a single way distorts reality too much) medians, these are considered dual carriageways instead and therefore should be drawn as two ways (this means, use of median on oneway=yes is invalid unless an exception for a certain traffic mode is set). The rules are comparable to embedded_rails i.e. if you can't drive onto the trackbed, you wouldn't use median on that situation either. Separation on cycleways are tagged with cycleway:separation=* instead, especially because these exist more to the side than the middle of the road, though an exception can be made when the road is normally one-way and the cycle lane is a contraflow lane.

It also should not be used to mark the existence of lane markings. To denote these, use lane_markings=* instead (note that median=yes implies lane_markings=yes), if the divider is linear and not an area, use divider=* instead.

Rendering

In general, only renderers which render lanes need to take care of median=*. Most common renderers such as Carto don't show lanes, though some like OSM2World and the JOSM's and Road Attributes do and therefore should take care of median=*.

Features/Pages affected

• lanes=*
• Lanes
• Highways
• divider=median (deprecation thereof)

Comments

Please comment on the discussion page.