Key:tunnel

tunnel=* is used for roads, railway line, canals etc that run underground.

For some grade separated crossings it may however be debatable if the lower way is in the tunnel or if the upper way is on a bridge=*. In general, if the lower way is long and surround by earth it is almost certainly a tunnel; and if the lower way is short and the upper way is supported on concrete, brick on metal pillars / beams then that is almost certainly a bridge. There are however situations where it is a matter of personal judgement, but it is preferred to either tag the lower way as tunnel or the upper way as a bridge but not both.

Where the water from a smaller stream, drain or even cattle crossing passes under under a structure or building consider using tunnel=culvert in place of the tunnel=yes used for larger tunnels for roads or railways or canals.

For tunnels which are open on one side, often found on mountain roads or ways underneath a building, use covered=yes in place of the tunnel.

For a structure that carries water or another liquid some considerable distance then it may be more appropriate to tag it as a pipeline using man_made=pipeline.

How to Map

Split the way in question at the points were the tunnel starts and ends and add the tunnel tag. It is best to avoid having a tunnel continue to a junction that is not in a tunnel by splitting the way prior to the junction. It is also good practice to add a layer=-1 tag in most situations to indicate that it runs below features with a layer tag. Some people consider this to be unnecessary however. For metros/subways it is often convenient to use layer=-2 to accommodate underground passages for pedestrians between the tunnel and the surface.

Where the approach to the tunnel is in a cutting this can be identified with cutting=yes. Note that a layer=-1 tag is not required on a cutting or embankment given that the way is on 'modified ground level'.

It may also be useful to add maxheight=* and maxwidth=* if there are publicised restrictions and use access=* if there restrictions on use by certain classes of vehicle or user.

If the tunnel has a name this can be specified using tunnel:name=* although there is still some debate on the best method to include a name of the tunnel as discinct from the road/railway etc that goes through it. lit=* can be included to provide information about any lighting in the tunnel (or not).

Showing a tunnel that continues to the junction on the left (wrong) and that is terminated before the junction on the right (correct).

Rendering

Osmarender (version 4) renders tunnels as dotted outlines with lines for the abutting face.

Mapnik draws tunnels on highways with dotted outlines and a lighter fill color for the road and with curved color transitions on tunnel entrances.

Proposals

• Relations/Proposed/Bridges_and_Tunnels - group multiple tunnel elements with a relation