Proposal:Bridges and Tunnels

Bridges and Tunnels
Proposal status:	Proposals with undefined or invalid status (inactive)
Proposed by:	David.earl
Tagging:	type=bridge;tunnel
Applies to:
Definition:	set of tags and members making a relation to represent a bridge or tunnel
Statistics:
Draft started:	2007-10-08

This is a proposal for a set of tags and members making a relation to represent a bridge or tunnel.

This does not deprecate the older methods such as bridge=*/tunnel=yes attached to a way which is still the simplest and easiest method to implicitly represent a bridge by adding a property to the way running over a bridge, but is an additional alternative for complex cases where the simple bridge as way or man_made=bridge area models are not deemed sufficient.

The bridge/tunnel relations:

• group together ways which share a common bridge: for example, a dual carriageway (divided highway) where both carriageways pass over the same bridge structure. In the absence of a bridge outline, a renderer would show bridge parapet symbols alongside only the outermost constituent ways. (can be done with man_made=bridge as well)

• allow the possibility to mark arbitrary objects as beeing on a bridge/in a tunnel (can be done with man_made=bridge as well - see Proposed features/Simplify man made=bridge mapping )

• allow the possibility that a bridge or tunnel may be independently named from the ways which it carries. (can be done with man_made=bridge as well)

• allow for properties of the structure to be represented (e.g., clearance).

• optionally identify a way showing the outline or "footprint" of the bridge or tunnel. For example, some oblique crossings use a more orthogonal structure where the road crossing occupies only part of the surface of the structure; or where there are buildings on the bridge perhaps so the bridge is wider than the road (if any) it supports.

Some alternatives exist:

• man_made=bridge and Proposed features/man made=tunnel can be used to draw a simple outline, represent multilelvel bridges/objects, group objects and ways together and assign attributes to the whole structure rather than single ways/object.
• Bridge3D can be used for micro mapping bridges

Tags

Key	Value	Discussion
type	bridge or tunnel	Indicates this relation represents a bridge/tunnel.
bridge	any valid value of bridge=*	Bridge type as found in Key:bridge#Values. This should be the "overall type" of the bridge, can be left empty if bridge consists of more sections with conflicting types or if the value would be "yes".
bridge:movable	any valid value of bridge:movable=*	Type of movable bridge if bridge:type=moveble
bridge:structure	any valid value of bridge:structure=*	Bridge structure
layer	layer (number -5..+5)	The layer of the bridge. In rare complex cases a single bridge may be partitioned in several sections with different layers in which case this field would be probably best left empty as the individual ways ought to be mapped correctly anyway.
name	a name	The bridge or tunnel is known by this name (e.g., "Tower Bridge")
ref	a reference	Bridges are sometimes numbered (e.g., along UK canals)
toll	yes	it is a toll bridge/tunnel (but does this make sense for the relation? What if it's a free bridge over a tolled canal?) This is a feature of the footway, the cycleway and the motorway through a tunnel and over a bridge and can be different!
height	height in meters	Bridge height measured from ground to top (usually derived from a signpost on the bridge or its side)
length	length in meters
maxheight	height in meters	the maximum permissible height for bridges/tunnels with limited clearance (usually derived from a signpost on the bridge) (as per existing tag in Map features) This is a feature of the footway, the cycleway and the motorway through a tunnel and over a bridge and can be different!
maxweight	weight in tonnes	the maximum permissible weight for a vehicle passing over the bridge (usually derived from a signpost on the bridge) (as per existing tag in Map features) This is a feature of the footway, the cycleway and the motorway through a tunnel and over a bridge and can be different!
maxwidth	width in meters	the maximum permissible width for a vehicle passing over the bridge/in the tunnel (usually derived from a signpost on the bridge) (as per existing tag in Map features)This is a feature of the footway, the cycleway and the motorway through a tunnel and over a bridge and can be different!
operator	operator name	The party responsible for the bridge; e.g., "Network Rail".

Members

Way or node	Role	Recurrence?	Discussion
	across / through	zero or more	the ways supported by (on top of) a bridge / passing through a tunnel. Members without a role should be treated as across / through.
	under	zero	the ways passing under a bridge. This does not in any any way obviate the need to use layer=* correctly and seems useless if not harmful at this point.
	outline	optionally one	a way forming the outline "footprint" of a bridge or tunnel. It might be a good idea to tag the outline additionally with man_made=bridge
	edge	zero or more	alternative to outline, a set of ways which form the edges. Rather than drawing an area, a renderer could then draw the parapet marks as now along these ways. The interior of the bridge should be on the right of these ways (so if we were modelling a simple bridge using this technique, there would be two ways running in opposite directions parallel to and either side of the road-way which passes across the bridge; but this is generalisable to more complex cases: for example, consider a bridge which has a meeting of three ways on top). If neither outline nor edge is given, the "across"/"through" ways would be used to derive a nominal outline for rendering purposes for example.
	on_bridge	zero or more	additional objects located on the bridge, those should be additionally tagged with location=bridge and layer as described here.
	in_tunnel	zero or more	additional objects located in the tunnel.

Usage

type=bridge	type=tunnel

Discussion

Please discuss in the talk-section