Kaart: Tunnels, Bridges, Fords, Etc./sandbox

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Introduction

This page provides information about tunnels, bridges and fords and how to tag them.

Prerequisites

You will need to know how to digitize features using JOSM, ID Editor and Rapid. In addition, you should know how to verify tag key combinations using the Wiki.

Skill Instruction

To better understand how each of these features works and is tagged we need to break them down so you can understand how they all work together.

Layers

Layers play a critical role in describing the relationship between crossing or overlapping features. Understanding how to use layers properly will help you improve the tagging of tunnels and bridges.

There are 3 types of layer tags: 1. Negative layers 2. Ground level 3. Positive layers

This example shows a variation of the different layer=* values including two railways that can't be seen from satellite imagery.

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Negative Layers These tags are used to show that a feature passes under another feature(s). Their values are between -1 and -5. They are commonly used with tunnel=* features.

Ground Level This layer is the base standard for all features until a layer tag is added to a feature. The value for ground level is layer=0, but this tag should NOT be used as it is already implied.

Positive Layers These tags are used to show that a feature passes over another feature(s). Their values are between 1 and 5. They are commonly used with bridge=* features.

How to Tag

Here are some guidelines on how to use layer=* tags correctly.

  • Layer tags should only be added at the precise location where they apply (same for tunnels and bridges).
  • DO NOT connect a crossing feature directly to a layer where they cross as this confuses the relationship between the features as well as causes other issues.
Here's an example of this:
View of bridge in satellite imagery Underlying ways connected to bridge How routing is affected
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  • Features crossing above or below a feature with a layer will have a higher or lower layer=* where they apply.
  • layer=* tags may be used in combination with other tags such as building=*, covered=*, highway=elevator, etc.
  • Layer has NOTHING to do with height. It simply shows the relations between crossing or overlapping features and will affect the order feature visually render in on the map.
    • Negative values do not imply that the feature is underground.

Things to keep in mind:

  • NEVER use layer=0. This is already implied.
  • DO NOT use layer=* tags to resolve warnings of crossing or overlapping features.
    • Use available resources to fix it correctly or leave it alone so it can be easily found and fixed later.
  • DO NOT add layer tags to long features without first verifying how long the layer tag applies to that feature.
    • This helps avoid or points out potential issues with other crossings with that feature.
  • Use the smallest applicable value.e.g. Only use layer=-2 if the tunnel passes under a tunnel that is layer=-1.
  • Split the ways and adjust layer tags accordingly to accurately represent the relationship of all the features.
  • The Kaart Style will flag tunnels/bridges that are missing a layer=*.

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Tunnels

Tunnels describe a feature's relation to an overlying way. It is important to input them correctly. Tunnels are used when/where a bridge tag would not be appropriate. They are often used for waterways that are channeled under roads.

Common tunnel=* tags include:
tunnel=yes This is the most common tag.
tunnel=culvert A tunnel for waterway features passing under a road, building or structure.
tunnel=building_passage A tunnel that passes through a building.
Additional info on tunnels can be found on Key:tunnel

Tunnels in OSM have three parts to them: 1. The road leading into the tunnel 2. The tunnel itself 3. The road leading from the tunnel

How to Map

  • Use available satellite and ground imagery to confirm the tunnel.
  • Split the way at the start and end of the tunnel.
    • Make sure there. is a space between the tunnel and any intersections.
  • Add the appropriate tunnel=* and layer=* tag.
Correct Incorrect
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Unique Tunnels/Scenarios

There are some unique scenarios and tunnels that don't always follow the common tagging scheme for tunnels.

covered=* Used for covered passages that are open on one or more sides along the way.e.g. Gas station roof over pumps.
tunnel=building_passage Normally does not need a layer tag since the passage is commonly on ground level, but may require one in cases where there are multiple layers/levels in the building.e.g. Trunk road in Hong Kong
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tunnel=culvert
  • Used when water passes under a way, building, or structure.
  • These are easier to verify with ground imagery than satellite imagery.
    • In satellite imagery, look for a lack of shadows near the crossing highway and for the waterway to narrow where the crossing occurs.
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For more information about tunnel types tags you can reference the Key:tunnel page.

Naming

Tunnels: Tunnel naming is very similar to how bridges are named with some differences.

There are a couple ways to add names to a tunnel:
Street signs. There are two cases that may apply:
  • Street sign is the tunnel name that is added as the name=* tag.
  • Street sign is the same as the current street name; extend the street name and add the tunnel name as tunnel:name=*.
Different street names and no tunnel name: Extend one of the names and add the other as an alt_name=*.

For more information on names see the Kaart: Name Tags/sandbox page.

Routing

There are some important things to keep in mind when it comes to routing on tunnels.

  • Make sure the tunnel doesn't end at an intersection.
    • There should be a spacer on either side of the tunnel or it should connect to other tunnels.
  • Don't connect overlying ways to a tunnel.

Cutting

Cutting is when a road cuts down into the ground. These are sometimes found before tunnels but are more common on major raods that allow you to bypass an area.

How to map:

  • Use available imagery to identify where the cutting starts/ends.
  • Split the ways and add the appropriate cutting=* tag.
    • These do not commonly need a layer=* tag unless there are multiple layers of objects that need to be distinguished.

Pedestrian Tunnels

Pedestrian tunnels are footways or other pedestrian features that pass under other features such as highways.

How to map: These follow the same tagging scheme as tunnels.

  • Use available imagery to confirm the tunnel.
  • Split the way at the start and end of the tunnel.
    • Make sure there is a spacer between the tunnel and any intersections.
  • Add the appropriate tunnel=* and layer=* tag.

For additional information about pedestrian features see the Kaart: Pedestrian Features/sandbox page.

Bridge

A bridge is an artificial construction that spans features such as roads, railways, waterways, or valleys, and carries a road, railway or other features.

Bridges in OSM have three parts to them: 1. The road leading into the bridge. 2. The bridge itself. 3. The road leading from the bridge.

How to Map

  • Use available imagery to confirm the bridge.
  • Split the way at the start and end of the bridge.
    • Make sure there is a spacer between the bridge and any intersections.
  • Add the appropriate bridge=* and layer=* tag.
Correct Incorrect
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Naming

Bridges: Bridge naming depends on the context of each bridge and what information is available. e.g. signage, what the data looks like, tags that were used, etc.

There are a few ways to add names to a bridge:
man_made=bridge This tag is added as a polygon around the bridge and is attached to the bridge. The purpose of this is to add additional information about the bridge like the bridge name, the type of bridge, etc.
Street signs. There are two cases that may apply:
  • Street sign is the bridge name that is added as the name=* tag.
  • Street sign is the same as the current street name; extend the street name and add the bridge name as bridge:name=*.
Different streets names and no bridge name: Extend one of the names and add the other name as an alt_name=*.

For more information about naming see the Kaart: Name Tags page.

Routing

There are some important things to keep in mind when it comes to routing on bridges.

  • Make sure the bridge doesn't end at an intersection.
    • There should be a spacer on either side of the bridge or it should connect to other bridges.
  • Don't connect underlying ways to a bridge.

Embankment

An embankment is a gradual, raised section of road usually made out of dirt or concrete leading up to a bridge.

How to map:

  • Use available imagery to identify the embankment.
  • Split the ways where the embankment starts/ends.
  • Add the appropriate embankment=* tag.
    • Embankments do not commonly have a layer=* tag unless there are multiple layers of objects that need to be distinguished.

Pedestrian Bridges

A pedestrian bridge is a type of crossing that crosses over a highway or other features.

How to map: These are tagged the same way as bridges.

  • Use available imagery to confirm the bridge.
  • Split the way at the start and end of the bridge.
    • Make sure there is a spacer between the bridge and any intersections.
  • Add the appropriate bridge=* and layer=* tag.

For additional information about pedestrian features see the Kaart: Pedestrian Features/sandbox page.

Bridge/Tunnel Classifications

Bridge/tunnel classifications are determined based on the classification of the roads they connect. The specific scenario influences how the bridge/tunnel is classified:

Single Road Transition: When a single road changes from one classification to another, the bridge/tunnel will adopt the higher classification. This ensures continuity of the higher-priority route.

Example: A collector road transitioning into an arterial road would result in the bridge/tunnel being classified as arterial.

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Parallel Roads Connection: If the bridge/tunnel connects two parallel roads of different classifications, it will take on the lower classification. This approach preserves the integrity of the higher-classified road by not altering its intended function.

Example: A bridge/tunnel connecting a local road to a collector road would be classified as local.

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Fords

A ford is a place where a waterway can be crossed by a vehicle without a brdige.

  • Use all available imagery to confirm if the crossing is traversable by vehicle.
    • Look for tracks on both sides of the waterway as well as other clues or indicators.

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How to Map

There are a few different. wayss to tag fords depending on the data.

If there's a waterway and a road:
  • Connect the waterway and road with a node and add ford=yes to the node.
  • If there's no waterway, add the ford=yes tag on a node where the crossing is visible.
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If there's a waterway polygon and a road: Split the road where it intersects with the polygon and connect the two features, then add ford=yes to the way that crosses the polygon.
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If there's a waterway polygon, waterway and a road: Split the road where it intersects with the polygon and connect the two features, then add ford=yes to the way that crosses the polygon. In addition, connect the way and the waterway with a node and add ford=yes to the node.
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Intermittent/Seasonal

Some roads are only traversable during certain times of the year, day or seasons. This can be very useful information to add as this will impact routing for that area.

Intermittent:

This tag is used when a waterway or body of water does not always contain water. The tag intermittent=yes is typically added to the ford=yes node or the waterway/feature that is intermittent.

Seasonal:

This tag is used when a regular occurrence happens during certain conditions. e.g. rivers drying up in dry seasons and roads being snowed in during winter. The tag seasonal=* (commonly seasonal=yes) is typically added to the ford=yes node or the waterway/feature that is seasonal. Also commonly used with intermittent=yes.

Practical Application

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