Proposed features/Bridge types
| Bridge Types - Key:bridge, Key:bridge_type | |
|---|---|
| Status: | Draft (under way) |
| Proposed by: | choess |
| Tagging: | bridge, bridge_type=* |
| Applies to: |  , 
|
| Definition: | This proposal is orthogonal to Relations/Proposed/Bridges and Tunnels. |
| Rendered as: | Except for those values indicating that a bridge no longer exists, these bridges should be rendered in a fashion similar to "bridge=yes". |
| Draft start: | 2012-02-04 |
| RFC start: | |
| Vote start: | |
| Vote end: | |
Contents |
Proposal
This proposal adds additional values to the "bridge" key and codifies the "bridge_type" key to allow a more extended description of the load-bearing form and other notable characteristics of bridges, including covered bridges and various types of movable bridges.
Rationale
Many mappers would like to enter additional information about the bridges they map, particularly the architecture, material, and function of the bridge. This additional information is often of utility to consumers of the map. For instance, covered bridges are widely regarded as picturesque, and are often of historic importance. Being able to identify these bridges may be of interest both to tourists and preservationists. Moveable bridges are potentially of significance in routing, both for water traffic passing beneath and surface traffic which may be interrupted by their opening.
While taginfo reveals that ad hoc tagging schemes exist for some of this information, they are relatively unsystematic. Only a few of these tags have been officially documented, and the alternative values are not supported by common renderers. By presenting a regularized scheme of common bridge information, this proposal should make it easier to store data on the majority of bridges while providing proper rendering support.
Examples
There are about 1,400,000 bridges currently mapped throughout the world, most of which are simply tagged "bridge=yes". This proposal would probably regularize the alternate values for about 1,500 bridges, but it would also allow adding additional information to many of the 1,400,000. While generic beam bridges and culverts are unlikely to be tagged, this provides a structured way to add information about more unusual and charismatic bridge types. Bridgehunter.com currently tracks about 38,500 bridges in the United States, and does not claim to provide complete coverage, to give an idea of the number of bridges that might be annotated with type information.
Tagging
The new values proposed are divided among 2 keys: bridge and bridge_type. The "bridge_type" key has already been used in mapping bridges in Haiti, consistent with the Humanitarian OSM Tags/Humanitarian Data Model. Its values (arch, beam, suspension, etc.) refer strictly to the load-bearing architecture of the bridge. This proposal is compatible with and extends this use of the key, adding additional types of load-bearing architecture. Sources drawn on to provide the different bridge values include: current taginfo, the Bridge and Trestle Handbook, 4th ed., Paul Mallery, and the English Wikipedia and Wikimedia Commons category systems for bridges.
It may be asked why the additional "bridge_type" key is necessary, rather than simply making use of the "bridge" key. This is because some of the values to be used with the "bridge" key, such as "swing" or "covered", may be compatible with more than one type of load-bearing architecture. For example, a swing bridge may be a girder (beam) bridge or a truss bridge; both "beam" and "truss" are currently-used values of "bridge_type". Using two keys allows information about both functions to be preserved without overloading a single key with combinations. The principal adverse consequence of this decision is that it requires converting the current "bridge=suspension" (761 instances) to "bridge_type=suspension".
Bridge key: ways
| Key | Value | Comment | Photo |
|---|---|---|---|
| bridge | covered | A covered bridge has a roof and fully or partly enclosed sides, usually to protect the bridge deck from deterioration. | 
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| bridge | moveable | Moveable bridges contain a span that can be moved up or to the side, often to provide greater clearance for traffic moving beneath the bridge. This value should be used for moveable bridges not readily categorized into one of the types below. | 
|
| bridge | swing | A type of moveable bridge, a swing bridge contains a span supported by a pivot resting on a pier, either at the center or towards one end of the span. Rotating the span on the pivot opens or closes the bridge. | 
|
| bridge | lift | A type of moveable bridge, a lift bridge contains a span which rises vertically while remaining parallel to its closed position. The span is suspended between lift towers at each end when open. | 
|
| bridge | bascule | A type of moveable bridge, a bascule bridge contains one or two spans, one end of which is free and swings upwards. A counterweight at the pivoting end of the span or spans balances the weight as the free end rises. Although sometimes called a "drawbridge", that term is applied more strictly in this scheme (see below). | 
|
| bridge | drawbridge | A type of moveable bridge similar to the bascule, as one end of the bridge is free and swings upwards. However, this type of bridge is raised by chains attached at the free end. | 
|
| bridge | transporter | A bridge where a segment of roadway or footway is suspended from cables and carried back and forth like a gondola. | 
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| bridge | viaduct | A bridge composed of a series of short spans. The spans may be arches, girders supported by piers, etc. | 
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| bridge | trestle | A type of viaduct where each span is supported by a rigid frame, usually called a "bent" rather than a pier. | 
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| 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. | 
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| 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. | 
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| bridge | boardwalk | A plank walkway over wet or otherwise difficult terrain, usually low to the ground and supported by posts. | 
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Bridge_type key: ways
| Key | Value | Comment | Photo |
|---|---|---|---|
| bridge_type | arch | In an arch bridge, the span is supported by a curved arch, which transfers some of its weight into horizontal thrust against the abutments. | 
|
| bridge_type | beam | In a beam bridge, the load is transferred entirely to a span resting on a support at either end, without additional reinforcement. | 
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| bridge_type | truss | In a truss bridge, the span consists of a series of interlocking triangular units which bear the load. | 
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| bridge_type | floating | A bridge whose load is supported by floating on water, rather than resting on fixed supports. Typically a pontoon bridge. | 
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| bridge_type | suspension | A bridge where the load is supported from a cable under tension, attached to anchorages at each end of the bridge. In most, but not all, suspension bridges, the cables are suspended between towers near each end of the bridge. | 
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| bridge_type | cable-stayed | A bridge where the load is supported by cables radiating from the tops of towers resting on supports along the line of the bridge. | 
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| bridge_type | culvert | A culvert is a pipelike bridge, used to convey water (possibly intermittently) underneath a structure. When the culvert is embedded or buried in an embankment, it should be tagged as "tunnel=culvert"; if the road is directly supported by the structure of a culvert, it may be tagged with "bridge_type=culvert", or as one of the two types below, if known. | |
| bridge_type | culvert_round | A culvert (above) round in cross-section. | 
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| bridge_type | culvert_box | A culvert (above), roughly square or rectangular in cross-section. | 
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Bridge key: nodes
| Key | Value | Comment | Photo |
|---|---|---|---|
| bridge | pier | An intermediate, upright support beneath a bridge. Known as a "bent" in trestle bridges. | |
| bridge | abutment | A support for one end of a bridge. | |
| bridge | lift_pier | A support for a lift bridge over which one of the lift towers stands. | |
| bridge | pivot_pier | A support for a moveable bridge on which the bridge pivots, either horizontally (as a swing bridge) or vertically (as a bascule or drawbridge). |
Deprecated bridge key values
- bridge=causeway: If water normally passes over the causeway, it should be tagged as "ford=yes". If water runs over it only at high water (Australian usage), it should be tagged as "bridge=low_water_crossing". If the causeway is built above water, it should be replaced with "embankment=yes", showing a short culvert or bridge at the point(s) where water passes beneath it.
- bridge=suspension: Moved to "bridge_type=suspension".
Applies to
Most of the tags are intended to be applied to ways, although they might be applied to a node when detail is lacking to properly map the bridge. The exceptions are "bridge=pier", "bridge=lift_pier", "bridge=pivot_pier", and "bridge=abutment", which are intended to be applied to single nodes.
Rendering
In general, these proposed values should be mapped in the same way as "bridge=yes", the current generic bridge rendering. Possible refinements might include connecting the sides at the ends of "bridge=covered", making it appear as a rectangle rather than a pair of parallel lines.
Features/Pages affected
The Key:bridge page will be affected; the new values will need to be added to the "Values" section, and a number of the proposed values under "Proposals" will be removed. It may also be useful to create a few examples showing the use of, e.g., "bridge=bascule", "bridge_type=truss", "bridge=pier" and "bridge=pivot_pier" to create a detailed representation of a moveable bridge. A new Key:bridge_type page will need to be created to cover that tag.
Comments
Please add comments on the proposal here.
