Proposed features/Snow chains

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Snow chains
Status: Proposed (under way)
Proposed by: Trapicki
Tagging: snow_chains; snow_chains:conditional; snow_chains:variable; highway=chain_up_area=*
Applies to: way
Definition: Requirements (possibly with conditions and variable) to put snow chains on your vehicle when driving on this highway, with places reserved for putting on snow chains.
Drafted on: 2021-11-09
RFC start: 2021-11-11

Statistics

snow_chains=*


snow_chains:conditional=*


snow_chains:variable=*


snow_chains:on_demand=*


highway=chain_up_area


Proposal

Tags related to snow chains:

  • Restrictions on roads regarding snow chains
  • Places to put on snow chains (which are dedicated and usually parking restrictions applies)
  • Vehicle properties "snow_chains" and "winter_tyres" for conditional tags

Scope

What is not part of this proposal:

  • Legislation: In some countries (e.g. Austria), some vehicles (vehicles > 3.5 t) under certain conditions (always at ice or snow) are required to use snow chains. In some areas of France it's compulsory to carry snow chains during winter. This legal requirements shall not be tagged with tags from this proposal.
  • Winter equipment: Winter tyres, studded tyres, lugs and the like are related to snow chains, but not scope in this proposal, except for the vehicle property "winter_tyres" used in conditionals.
  • Traffic signs: Traffic Signs announcing restrictions related to snow chains are not part of this proposal, because this would be part of a different aspect with a much wider scope. The aspect that the restriction may be variable is covered in the proposal.

Rationale

White tyre covered in chains on blue circle
"Snow chains required" sign in Austria
Black snowflake on white rectangle
"when ice or snow" additional sign in Austria

In areas where roads are covered in snow and ice during winter, on sufficiently steep roads motorized vehicles may be required to have snow chains (tyre chains) attached. On some road sections like tunnels snow chains may be prohibited.

On some roads, special areas are reserved for putting on/laying/ chains / chaining up ("chain-up areas", "chain bays") or removing them, which are reasonable flat, allow rolling the vehicle to facilitate chaining up, and allow to accelerate safely also in heavy snowfall. Most probably these areas will have parking restrictions to ensure that in case they are needed, space is available, and vehicles leave as fast as possible.

Often, the requirement to use snow chains is issued on demand by, indicated by special road signs that can be covered, flipped open/close, turned sideways, unmounted, or are operated from remote electrically. Tagging on-demand restrictions is important to let mappers and users understand that the road sign may be presented different in different conditions. This prevents accidental removal of tags and allows to understand that an ineligible road sign may be active at some other time of year.

Usually the requirement for snow chains is conditional, most commonly restricted to conditions of ice or snow, but also certain types of vehicles (e.g. trucks, all wheel drive, weight), directions (e.g. downhill), or vehicle equipment (e.g. winter tyres, "winter equipment"); this may also apply to to on-demand snow chain requirements.

Even though this is quite common in the European Alps and other parts of Europe and the world (During Draft status: Please add your knowledge where snow chains are required by traffic signs in the world!) we do not yet have any tagging scheme for these things. But they are useful for several reasons:

  • It's part of everyday life of drivers/law enforcement/fire brigades in significant parts of the world.
  • For routing, it is important to know about existing or possible limitations or equipment that may be necessary, which is especially true for snow chains. As snow chains are only necessary and/or required under certain conditions this may change depending on the time one travels the route, it may even change on short notice during the journey. Knowing the possible limitations beforehand allows to adjust the route or equipment accordingly and consider the implications accordingly. Routes could also filter to not require winter equipment. In case snow chains are compulsory, places to put on snow chains (chain-up area, chain bay) may be shown/listed to help travellers.
  • There should be a map that shows or highlights these things. Map needs data.

Tagging

The decision to put on chains is usually understood to be judged by the driver evaluating the road condition; because (metal) snow chains may damage or excessively wear a road, chains should be removed whenever they are not required any more. Please keep in mind that a (conditional) requirement for chaining up may be shown on roads may also be shown when there is actually no snow, ice, snowfall or general winter conditions in the area. Use common sense.

Key snow_chains=*

way way

Applies to highway=* that apply to motorized vehicles.

Values:

  • snow_chains=required: Snow chains always required (traffic sign symbol: tyre with snow chains on blue circle)
  • snow_chains=prohibited: Snow chains never allowed, e.g. in tunnels (textual traffic sign, traffic sign symbol unknown)
  • snow_chains=carried: Snow chains have to be carried on the vehicle. This does not include the obligation to fit them immediately, this would have to be announced by a separate snow_chains=required (textual traffic sign).
  • snow_chains=recommended: Snow chains are recommended to be put on. This does not include the obligation to fit them or carry them on the vehicle. (textual traffic sign, e.g. USA, Idaho W 8-1301 [1] [2])

In most cases (at least in Central Europe), snow chains will be required conditionally (fixed rule, additional traffic signs) and/or on demand (issued by local authorities depending on the actual situation).

Subkey snow_chains:conditional=*

Standard Conditional restrictions. Use separate snow_chains=* for default value, probably default.

Examples of values:

Conditional vehicle properties "snow_chains" and "winter_tyres"

For Conditional restrictions, explicitly list "snow_chains" and "winter_tyres". This allows for better conditional restrictions and exceptions, both directly with snow_chains=* and other tags.

Subkey snow_chains:variable=*

Values:

  • snow_chains:variable=weather - Snow chains required as announced on site, on weather dependent decision of road authorities.
  • snow_chains:variable=no Traffic sign is known to be permanent. If it is not determined if the restriction is variable or not, do not set this value.

Can be combined with snow_chains:conditional=*: A restriction may be both conditional (e.g. specific type of vehicle) but only shown at specific weather conditions.

Subkey snow_chains:variable:type=*

Encodes the way how this sign is variable. Useful to tell users and mappers what to look for in case it's active but also in case it's inactive.

Sign may be flippable, foldable, turnable, coverable, removable, remote controlled electrically, flashing when active, rolling banner, etc..

Related tags:

Notes:

  • crossing:on_demand=* is similar, but not the same; it is more leaning towards "on request" then "if the situation requires it". snow_chains:on_demand=* is a subkey, and does not collide with crossing:on_demand=*
  • maxspeed:variable=* was my first though, but "variable" is usually used to indicate a restriction (speed limit) that always applies and is changed depending on conditions, and moreover "on demand" is more self-explaining, and easier to understand and remember.

Value highway=chain_up_area

node node, way way, area area. See below for details.

For areas that are primarily dedicate to putting on/off snow chains. No distinction is made for areas intended to specifically chain-down/put off chains in the tag; name=* may reflect the actual intended purpose.

Related to highway=rest_area and highway=emergency_bay, but with a different purpose:

Identify your highway stopping area
Chain-up area Chain bay Rest area Emergency bay
Purpose chaining up chaining up resting, staying, refreshing, parking stop at emergency
Parking, extended stay? very probably not no yes no
Chaining up possible yes yes yes yes
All year open? no, only winter no, only winter. Maybe emergency bay all year. all year yes
Expected amenities optional: lighting optional: lighting, emergency phone parking area, toilets, picnic tables, waste baskets, lighting optional: lighting, emergency phone
Separation from main road yes no yes no
Tagged as area way or point area or point way or point

A rest area may be used to chain up, but a chain-up area may not be used as rest area.

name=* should be set only if known, as name=chain-up area [known name]. The areas may get named after a near known place, while not being that very place itself. name=chain-up area is wrong by Good practice: Don't use name tag to describe things

If there is a dedicated chain-up and dedicated chain-down area in close proximity, and a specific name is known, the purpose can be reflected in the name: name=chain-up area [known name] and name=chain-down area [known name].

ref=* should be tagged and rendered if numbered/coded. Example: In Australia, highest elevated chain area for a pass has ref=1, counting up descending from that one.

Note: This key could subsume Proposed features/amenity=chain bay. Differing to that proposal, I'd rather not call it "bay", because there exist ones that are more separated from the main road.

Related tags

incline=*

Examples

Tagging Explanation Note Image
Snow chains required when road is covered in snow or ice.
  • :conditional=* does not allow OR. Multiple conditions separated by ; have to be used.
  • The additional "snowflake" sign[1] requires separate conditions for both snow and ice. Other additional signs may state only snow or only ice.
  • Probably one of the default conditions.
Traffic sign "Snow chains" compulsory beginning with additional condition sign "when ice or snow" at Weinbergweg, Stattegg, Austria
Traffic sign "Snow chains" compulsory beginning with additional condition sign "when ice or snow" at Weinbergweg, Stattegg, Austria
Snow chains required when road is covered in snow or ice, but not for uphill driving AWD motor vehicles.
  • Last condition to match is valid.
  • AWD here means all-wheel-drive, not limited to off-road vehicles.
Traffic sign "Snow chains" compulsory beginning with additional condition sign "when ice or snow" and "ausgenommen bergwärtsfahrende Allrad-Kraftwagen" ('except uphill driving AWD motor vehicles') at L619 Weinebenestraße near Deutschlandsberg, Austria
Snow chains required, except for motorcars (Class N) with winter tyres.
File:Snow chains variable except winter tyre motorcar start Schanzsattel.jpg
Traffic sign "Snow chains" compulsory with additional sign "ausgenommen PKW mit Winterreifen" ('except motorcars with winter tyres'), beginning.
Sign can be rotated. When turned to face to approaching traffic: Snow chains required, except for motorcars (Class N) with winter tyres.
File:Snow chains variable except winter tyre motorcar start Schanzsattel.jpg
Traffic sign "Snow chains" compulsory with additional sign "ausgenommen PKW mit Winterreifen" ('except motorcars with winter tyres'), beginning.
Sign rotated to right, facing outside of the street to let it have no effect.
Named chain-up area Dedicated chaining up/down, not a highway=rest_area Note: image missing

Rendering

Road

For winter theme, add some bold/coloured/dashed(for snow_chains:conditional=* snow_chains:variable=*) highlighting. In a zoom level adequate to to importance of the road, start and end should be marked with a snow chain symbol Snow chains required

Chain-up area

Like resting area, but cooler colour (light violet) and with a symbol derived from chain-up area Symbol for hain-up area on maps. Can occur alongside parking sign, if parking is allowed and tagged.

Features/Pages affected

Related Topics

Informal listing for reference only, not part of the proposal.

Candidates

Road signs

  • In Austria[2][1], Germany, Italy, Switzerland, Czeck Republic and other countries a traffic sign for "snow chains required" exists and is in common use.
  • The UN Vienna Convention on Road Signs and Signals[3] defines
    • a snow chain sign as D, 9 "SNOW CHAINS COMPULSORY" and E, 21 / E, 22 "CHAINS OR SNOW TYRES RECOMMENDED".
    • Annex 5 F.7. "ROAD OPEN  OR  CLOSED"  sign: Sign E, 21, "ROAD OPEN OR CLOSED", shall be used to show whether a mountain road, particularly a section leading over a pass, is open or closed; the sign shall be placed at the entry to the road or roads leading to the section in question. The name of the section of road (or pass) shall be inscribed in white. On the sign shown, the name "Furka" is given as an example. Panels 1, 2 and 3 shall be removable. If the section of road is closed, panel 1 shall be red and shall bear the inscription "CLOSED1 ; if the section is open, panel 1 shall be green and shall bear the inscription "OPEN", The inscriptions shall be in white and preferably in several languages. Panels 2 and 3 shall have a white ground with inscriptions and symbols in black. If the section of road is open, panel 3 shall remain blank and panel 2, according to the state of the road, shall either be blank, or display sign D, 9, "SNOW CHAINS COMPULSORY", or display symbol E, 22, "CHAINS OR SNOW TYRES RECOMMENDED". This symbol shall be black. If the section of road is closed, panel 3 shall show the name of the place up to which the road is open and panel 2 shall display, according to the state of the road, either the inscription "OPEN AS FAR AS", or symbol E, 22, or sign D, 9.One "Road Open or Closed" sign, for the "Furka" example in the Convention, is located at 500 m west of Hospental, CH. A similar sign for the three passes Furka, Grimsel and Gletch is located just north of Oberwald, CH. Road directions with "Road Open or Closed" style information can be found just south of Ulrichen, CH.

Legal requirements

By Good practice: Don't map your local legislation, if not bound to objects in reality this proposal is not concerned with regional or national regulations. Nevertheless it is important to interpret the actual road signage in context of the legal regulations.

Pages like

could be created. A very good start would be https://de.wikipedia.org/wiki/Winterausrüstung_(Straßenverkehr) which is unfortunately German only.

External discussions

Snow Chains

Variable Message

Mailinglist [Tagging] Billboard or something else 2019-10/11

Version/Changes

Version Change Discussion Topics
0 Last Draft
1
  • Chain up area and chain bay in relation to rest area and emergency bay
2
  • Values: yes/no => required/allowed/prohibited; chain-down; naming; legal requirements
3

Comments

Please comment on the discussion page.

General References

  1. 1.0 1.1 | StVO §54 Z. 5 lit. f "Diese Zusatztafel weist darauf hin, dass das Straßenverkehrszeichen bei Schneelage oder Eisbildung auf der Fahrbahn zu beachten ist." in RIS
  2. | StVO §51 lit. b Nr. 22 Gebotszeichen "SCHNEEKETTEN VORGESCHRIEBEN" in RIS
  3. https://treaties.un.org/Pages/ViewDetailsIII.aspx?src=TREATY&mtdsg_no=XI-B-20&chapter=11&Temp=mtdsg3&clang=_en