|The carriageway reference used for maintenance and emergency services.|
|Used on these elements|
|Status: de facto|
|Tools for this tag|
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.
|carriageway_ref=Re||Right/forward main carriageway (hoofdrijbaan rechts).|
|carriageway_ref=Li||Left/backward main carriageway (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.|
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).
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 reference values can be considered common knowledge because they are given on wikipedia:Driver location signs signs (e.g. M27 B 2.8, as seen in the image right) and are also printed upon the emergency telephones.
- What is a link road according to the road operator is not necessarily always a link road according to OpenStreetMap conventions, and vice versa.