Where the lower feature is surrounded by earth then the lower feature should probably be tagged using tunnel=* instead. It is sometime, however, a matter of judgment as to whether to tag a particular situation using a bridge or a tunnel. Do however avoid using both a bridge tag for the upper way and a tunnel for the lower way for the same crossing.
How to map
Split the upper way at each end of the bridge (which is where it joins solid ground) and add bridge=yes to the central section. It is good practice to not let a bridge terminate at a road junction or similar. The bridge should either end before the junction (the normal situation) or in cases where the junction is actually 'in mid air' itself then the other ways joining the junction should also be made into bridges for the relevant sections.
Bridges should have a layer=*, for simple crossings almost always layer=1 but other values may be appropriate for complex crossings. A ramp at an end of a bridge is not part of the bridge and can be tagged as embankment=*. An embankment should not have a layer tag in most cases.
The portion of a bridge between two of its supports is known as a span. Some bridges have one span, others many. The way in which individual spans are supported is often of mapping interest. Different types of spans (e.g., arch, beam, truss) can be described using the tag bridge:structure=*, while the supports beneath multiple spans and at the end of bridges can be described with bridge:support=* if warranted. It may be necessary to split the way in multiple places along the bridge when the bridge contains more than one type of span. Certain arrangements of spans use bridge=*: see the description below of bridge=cantilever, bridge=trestle, and bridge=viaduct. Other bridges with specialized properties are also listed below.
If the bridge has a maximum weight or length then add a maxweight=* or length=* to the upper way. If there are restrictions on the class of vehicles or users of the bridge use the access=* tag. If there are height limits for vehicles using the lower way (passing under the bridge) then add height=*, maxheight:marine=* to a node or a short length of the lower way. Some bridges are movable: a span or spans can be displaced, providing a greater overhead clearance for the lower way. Such bridges should be tagged with bridge=movable. As with the architecture of bridge spans, the mechanism by which a bridge moves is often of mapping interest, and can be specified in greater detail with bridge:movable=*. This tag can also be used to indicate bridge spans which once moved and are now fixed shut.
Where the bridge has a name there are a number of options for tagging. The one chosen is partly personal choice but may also depend on the significance of the bridge:
- Use the name field itself to hold the name of the bridge rather than the name of the road itself. For example London Bridge, in London, is named 'London Bridge' in OSM  and . The southern approach is named 'Borough High Street' and to the north the road is known as 'King William Street'. By way of comparison tthe Ordnance Survey have half of the bridge named 'Borough High Street' in OS Locator and Google Maps names one direction Borough High Street and the other direction London Bridge (Jan12). In reality the bridge probably has a road name and a bridge name and the road name probably does legally change in the middle of the bridge. This approach has the advantage that it will get rendered.
- Use the street/road name for the name field and put the name of the bridge in bridge:name=* as has been done for Stoke Bridge in Ipswich where both approaches to a minor named bridge are the same. By way of comparison Google also calls it Bridge Street.
- Use the proposed Relations/Proposed/Bridges and Tunnels to hold the bridge name.
- The proposed man_made=bridge can be used to hold bridge specific-attributes like name, reference, etc.
If the bridge has former names these can be tagged using bridge:old_name=*. A bridge reference can use bridge:ref=*. When using the proposed relation or man_made=bridge the keys old_name=* or ref=* can be used. Bridges can also be annotated with wikipedia=* and other standard annotation tags. start_date=* can be used to indicate the date on which the bridge was opened for traffic.
Don't use the tag building=bridge just for for marking bridges (their outlines). For such purposes you can use the proposed man_made=bridge. The tag building=bridge refers only to buildings which are used as bridges.
Bridges with several roads/ways or additional features
In case a bridge is represented by several ways or carries additional features there are currently two proposed ways to indicate this:
- With the proposed man_made=bridge simply the outline of the bridge is drawn. The roads/ways passing the bridge are connected to the outline. All bridge-specific attributes like layer, name, reference, etc. can be tagged directly on the outline. In case of bridges with multiple levels the proposed relation bridge has to be used additionally.
- When using the proposed relation bridge all features of the bridge have to be members of the relation and all bridge-specific attributes can be tagged in the relation. In case the bridge has multiple levels only the relation can be used in order to group together all objects of the bridge.
Bridges and waterway routing
Bridges are landmarks and can pose significant obstacles/hazards for navigability.
Many types of bridges not listed in the table below can be tagged with either of
|bridge||yes||Non-specific bridge tag, possibly combined with other bridge:* tags|
|bridge||aqueduct||A longer structure for carrying a canal or fresh water. Consider using historic=aqueduct for significant ancient aqueducts.|
|bridge||boardwalk||A plank walkway over wet or otherwise difficult terrain, usually low to the ground and supported by posts.|
|bridge||cantilever||A bridge where a span is supported at one end only. Usually, the free ends of two spans are fastened to one another, giving a longer clear span between supports.|
|bridge||covered||A covered bridge has a roof and fully or partly enclosed sides, usually to protect the bridge deck and members from deterioration. Consider also the combination bridge=*+covered=*.|
|bridge||low_water_crossing||Also known as an "Irish bridge", this is a low bridge which is engineered to carry vehicles above water at low flow levels and survive submersion at high flow levels. Consider also adding either ford=yes or flood_prone=yes on low-water-bridges that will sometimes be flooded on a seasonal and/or intermittent basis (see Discussion page).|
|bridge||movable||Movable bridges contain a span that can be moved up or to the side, often to provide greater clearance for traffic moving beneath the bridge. All such spans should be tagged with bridge=movable. Further information may be provided using bridge:movable=*. The fixed spans should be tagged separately, to make clear which part of the bridge is and is not movable.|
|bridge||trestle||A bridge composed of a series of short spans where each span is supported by a rigid frame, usually called a "bent" rather than a pier.|
|bridge||viaduct||A bridge composed of a series of spans, often short relative to its overall length. The spans may be arches, girders supported by piers, etc. For ways or features that raise a feature above the natural ground on mounds or earth walls, use embankment=*.|
This table is a wiki template with a default description in English. Editable here.
- Relations/Proposed/Bridges_and_Tunnels. This enables the grouping of several ways using the same bridge. The relation also enables tagging a reference number for the bridge.
- Use the proposed man_made=bridge for drawing the outline of larger bridges, grouping of all features of the bridge (especially multiple ways) and tagging bridge-specific attributes like name, reference, etc.
- Proposed_features/Bridge_Name - proposal for the name of the bridge itself
- Proposed_features/aqueduct - a proposal for historic aqueducts