Reporter: sladen
[Submitted to the original trac issue database at 5.41pm, Thursday, 25th June 2009]

Currently tunnels disappear under all sorts of things:

• Roads, rivers, seas, airports

and become invisible, disappearing without a trace. Examples:

• Helsinki: [http://www.openstreetmap.org/?lat=60.371&lon=25.0958&zoom=16&layers=0B00FTF 60.371,25.095] New harbour freight line, vanishing under a forest (Helsinki is full of trees...)
• Heathrow: [http://www.openstreetmap.org/?lat=51.467&lon=-0.462&zoom=15&layers=0B00FTF 51.467,0.462] Piccadilly, Heathrow Express, main entrance and cargo tunnels disappearing under Airport apron
• Thames: [http://www.openstreetmap.org/?lat=51.4648&lon=0.2743&zoom=14&layers=0B00FTF 51.464,0.274] Dartford Tunnels and CTRL Thames Tunnel disappearing under estuary
• Chunnel: [http://www.openstreetmap.org/?lat=51.0979&lon=1.2183&zoom=13&layers=0B00FTF 51.098,1.218] Channel Tunnel vanishing under English Channel

Ideally it would be possible to know where the tunnel goes when it passes under roads/forests/buidings and the like. Other existing map makers tend to do by rendering the tunnel as parallel dashed lines (or similar) on top of other features.

One possibility is rendering in two steps, a core centre, and outer lines. One being at the physical level (layer=) and one being overlaid higher-up.

Multiple stacked tunnels should continue to cross each other at the correct level (see Stratford, Kings Cross, etc... unless people have broken the sub-surface layering again).