Key:carriageway_ref

carriageway_ref is used to distinguish the two separated carriageways of a dual carriageway road. These markers allow emergency services and maintenance agencies to locate where incidents may be occurring, and people calling for breakdown services to locate themselves to their breakdown operator. This is very different from the ref=* tag, which is used to indicate the road number.

This key can be used on ways and nodes:

• use on highway=* for the carriageway reference of the road;
• use on highway=milestone for the carriageway reference indicated on the highway location marker.

European use

Belgium

In Flanders, on regional roads (gewestwegen) of operator=Agentschap Wegen en Verkeer, the following carriageway indications are in use on modern distance signs:

• For the main carriageway of a single-carriageway road:
  • carriageway_ref=h: main carriageway (hoofdweg)
• For the main carriageways of a dual-carriageway road:
  • carriageway_ref=h1: main carriageway with ascending distance (hoofdweg 1)
  • carriageway_ref=h2: main carriageway with descending distance (hoofdweg 2)
• For ramps:
  • carriageway_ref=a1: off-ramp with ascending distance (afrit 1)
  • carriageway_ref=a2: off-ramp with descending distance (afrit 2)
  • carriageway_ref=t1: on-ramp with ascending distance (toerit 1)
  • carriageway_ref=t2: on-ramp with descending distance (toerit 2)

Some motorways of operator=Bruxelles Mobilité - Brussel Mobiliteit in the Brussels-Capital Region have adopted the same scheme.

• 

  ref=N46
  carriageway_ref=h

• 

  ref=E313;E34
  int_ref=E 313;E 34
  nat_ref=A13
  carriageway_ref=h2

France

The Boulevard Périphérique of Paris displays carriageway indications I and E on milestone signs in the central reservation:

• carriageway_ref=I: clockwise inner carriageway (intérieur, shown on a red sign: carriageway_ref:colour=red)
• carriageway_ref=E: counter-clockwise outer carriageway (extérieur, shown on a blue sign: carriageway_ref:colour=blue)

Ireland

Ireland displays carriageway indications for the main carriageways of a dual-carriageway road:

• carriageway_ref=N: main carriageway in the northbound direction of the route
• carriageway_ref=E: main carriageway in the eastbound direction of the route
• carriageway_ref=S: main carriageway in the southbound direction of the route
• carriageway_ref=W: main carriageway in the westbound direction of the route

These are shown on location reference indicator signs, which look very similar to the driver location signs in the United Kingdom (see below).

Netherlands

Sign	Sign	Tag	Description
		carriageway_ref=Re	Right/forward main carriageway with ascending distance (hoofdrijbaan rechts).
		carriageway_ref=Li	Left/backward main carriageway with descending distance (hoofdrijbaan links).
		carriageway_ref=b	Link road or special situation indicated by a lowercase letter. Usually follows the letter assignment scheme from Beschrijvende Plaatsaanduidingsystematiek, e.g. b usually indicates an on-ramp to the right/forward direction. Sometimes mo is used on signs instead of m to avoid confusion with n, in these cases tag with carriageway_ref=mo. (What is a link road according to the road operator is not necessarily always a link road according to OpenStreetMap conventions, and vice versa.)

The road number to which the carriageway reference corresponds, is tagged as ref=* or official_ref=* (if both keys exist, the latter takes precedence). In some cases, an administrative road number is tagged with highway_authority_ref=*.

If the carriageway reference is not indicated on a sign, one may try to find it in a road operator database, e.g. Nationaal Wegenbestand. Older signs that omit the road number often also omit the Re/Li indications on the main carriageways.

In rare cases, bidirectional roads are assigned a different carriageway reference on each side. Use the keys carriageway_ref:right=* and carriageway_ref:left=* in these cases. Preferably reverse the way if needed to get the right/forward reference on the right side of the way (e.g. if you have carriageway_ref:left=Re, reverse the way so you get carriageway_ref:right=Re, which avoids a lot of confusion).

United Kingdom

In the United Kingdom the main carriageways of a road are usually designated "A" and "B", with the off sliproad from the "A" side being "J" and the on sliproad being "K", with "L" and "M" being used for corresponding "B" carriageway sliproads. "C" and "D" are used for where motorways or other divided highways have collector/distributor lanes, e.g. the M20 near Maidstone or M60 around Manchester. Some more complicated junctions use other references.

The values are given on driver location signs signs and are also printed upon the emergency telephones (emergency=phone).

• 

  Example driver location sign for
  ref=M27
  carriageway_ref=B

• 

  Carriageway identifiers commonly used at junctions