From OpenStreetMap Wiki
- links_higher=* / links_lower=* - these are used on a link road (eg highway=trunk_link), where the roads linked are of different status, to indicate the higher status and the lower status. If the link is split for some reason, the tags should be used on each link way, and reflect the status of the roads ultimately linked (and not the status of any link roads) example
- barrier=central_reservation and adjacent=trunk/primary/secondary - these are used along dual carriageways example. The adjacent tag is used in this instance to indicate the status of the road being divided.
- layer_change=yes - this indicates a ramp down to an underpass. Normally it makes sense to draw a circle at the end of a way to give a neat finish (end caps). If two connecting ways are at different levels this can produce some unwanted rendering artefacts. This situation is hard to identify for underpasses, so this tag acts as a flag example
- short_name=* - this has been used to provide a shorter name for an institution whose official name is too long for the size of it's site (so will tend not to appear, or overlap adjacent sites unreasonably)
- adjacent=yes - this indicates that the way is adjacent to another way of higher status, and sufficiently close that the rendering of them both in situ is likely to be confusing (eg a cycle track on a pavement next to a road).
- adjacent=semi - this means that the two ways are sufficiently far apart that their relative position isn't likely to be in doubt, but the lower-status one may need to be drawn on top (eg a cycle track alongside a dual carriageway). This should only be applied where the way runs in parallel, not where it turns to join or cross the road.
- crossing=* / crossing_ref=* on ways - the tags that normally appear on the node are applied to a crossing way. This allows symbols to be drawn that reflect the orientation of the crossing - such as a zebra. The tags are also applied to the node, for backwards compatability.
- oneway:reverse=block - this tag indicates that this is a oneway street where you have to go round the block. This separates "genuine" oneway streets from short sections of street where the directions are divided.
- mcn=oxford - this has been used to positively identify the main roads and the connecting routes through the centre that form the main cycle routes in Oxford. The use of this tag would probably be less comprehensive elsewhere in the UK (not all main roads would be sufficiently cycle-friendly). These routes are distinct in character to the lcn routes, with rather more traffic, and/or significant bus use.
- lcn:left=* / lcn:right=* - these tags are used on the road to show the local cycle network when it runs on one side of a road. These tags allow the renderer to draw a line to one side of the road, if they wish. There should also be a separate way alongside the road which will be a member of the lcn route relation, but this will be tagged adjacent=yes, to indicate that the rendering should be based on the tags on the road instead.
- lcn:left=track means it runs on a shared-use pavement (or separate cycle track).
- lcn:left=footway means it runs on the pavement unofficially (ie it's not formally a shared-use pavement, but people use it nevertheless).
- lcn:left=road means it runs on the road but in one direction only.
- lcn:left=lane means it runs on a main road, where cyclists normally cycle on the edge.
- lcn:left=service means it uses a service road alongside the the road.
- lcn:left=proposed_track means the pavement is scheduled to become shared to create a route, but it hasn't been implemented yet.
- lcn2=oxford / lcn2:left=* / lcn2:right=* - these tags are used for connecting routes between the lcn routes (but are otherwise identical to the lcn tags above)
- ncn:quiet=no - the ncn mostly coincides with quiet local routes, but is occasionally routed on busy urban roads. This identifies them
- service=* - this is added to a bus route relation to indicate the type of bus service.
- service=city - stopping bus running within the urban area
- service=country - stopping bus primarily running to destinations outside the urban area
- service=express - bus/coach service with limited stops linking urban areas
- service=tour - tourist sightseeing bus
- service=park_and_ride - limited stop bus to edge-of-urban-area car parks
- frequency=* - this is added to a bus route relation to indicate the approximate (weekday off-peak) frequency per hour (per direction). It may also be used at bus stops (typically where the service is less than hourly). journeys=* can be used with frequency=0 to indicate the number of journeys per day
- park_and_ride=* - this is used at bus stops that are served by Park and Ride services. The value can be the bus number or "yes".
- short_route_ref=* - this is used at bus stops to list the regular services that depart from there. The full list can be recorded using route_ref=*. Principally used at central stops.
- tour_bus_only=yes - this is used at bus stops that are only served by tour buses
- frequency:X13=* / frequency:4A=* - these are used on ways to indicate the frequency of services for a service that predominantly runs in combination with other services to provide a higher frequency, but on part of the route runs separately; these tags identify that joint-running does not apply