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QA for Turn Lane Mapping

Abhishek Saikia edited this page Aug 31, 2016 · 1 revision

While mapping turn lanes, there are a lot of scenarios are encountered in #153 and #144 mapping repos. All these scenarios are drafted in one place for validation purposes.

Different scenarios we came across while mapping

1. Parking lanes

In the U.S., when parallel parking spaces are marked, they are marked in one of three ways:


Here’s an example of the box marking style:


2. Counting number of turn lanes

If there are no clear cut demarcations on the road and yet cars are parked on either sides of the road, consider them as drive lanes. Case below:


3. Starting a turn lane

Turn lanes should begin exactly as per the marking in the imagery, not before or after.


4. Ending a turn lane

Turn lanes should terminate at the first highway junction after the start of the turn lane.


5. Turn lane forward

In case of bi-directional ways, the key turn:lanes:forward=* describes only the turning indications on the lanes in the same direction as the osm-way; while adding this we must view the road in the direction to the osm-way(on the direction where the osm-way arrow is pointing).


6. Turn lane backward

In case of bi-directional ways, the key turn:lanes:backward=* describes only the turning indications on the lanes in the opposite direction as the osm-way; while adding this we must view the road in the oppoiste direction to the osm-way(opposite to direction where the osm-way arrow is pointing).


Adding a turn:lanes:backward tag

7. Adding dual carriageways:

When finding roads mapped as single carriageway while the imagery shows clear separation between roads, split the road where the physical separation starts and add dual carriageways.


When to add dual carriageway?

  • Add Dual-carriage when
  • you see physical separation betweens roads
  • no relation is attached to the way.
  • Add turn:lanes tag to both the ways.

8. Bicycle lanes and road shoulders

Road shoulders and bicycle lanes are ignored from the lane count. Both these roads are lanes=2



lanes=3 for the above example, ignoring the two cycle ways

  • Ignore bicycle lanes even though they are in the middle;example below:


    The middle way is also a bicycle lane which is not counted while adding the lanes tag

  • Additionally, Strava global-heat cycle layer can used to verify if a particular lane is a cycle-way. tms[16]:{zoom}/{x}/{y}.png

9. Lane marked as a separate way

Do not add turn lanes in these cases where the only turn lane is already a mapped as a separate way.


10. Bidirectional turn lanes

These are the lanes marked with symbol representing both directions at a time.


Tag used for such lanes are turn:lanes:both_ways=*

Yellow lines on both sides of a lane also gives an indication of turn:lanes:both_ways=*

screen shot 2016-05-16 at 4 12 49 pm

screen shot 2016-05-16 at 4 13 00 pm

11. Mapillary Plugin to verify turn lanes

The imagery at some places is not very clear and at-times the turn-lanes are covered by cars. In situations like these Mapillary plugin can be used. If there is Mapillary imagery coverage in that area, they can used to verify the presence of turn-lanes.

Name of the plugin: Mapillary


12. Lanes with restricted access

These are the areas on streets which are restricted for vehicular traffic.

screen shot 2016-03-15 at 3 36 36 pm

screen shot 2016-03-14 at 4 46 03 pm

screen shot 2016-03-14 at 4 46 29 pm

In the above cases the areas with markings on the roads are not considered as a lane

13. Reverse direction turn lanes

These are the lanes specifically categorized to take U-turn or reverse-turn.

screen shot 2016-03-14 at 2 25 28 pm

14. The order of the directions and valid combinations of values

  • none itself is valid value but not in conjunction with other

  • turn:lanes=none|right is equal to turn:lanes=|right - we use none for "better readability"

  • 👎 turn:lanes=left||none|merge_to_right - this combination of values is valid but there is mixing none and || (empty) - this is not good choice.

  • 👍 turn:lanes=left|none|none|merge_to_right or turn:lanes=left|||merge_to_right

  • turn:lanes=none|none|none or turn:lanes=|| - in this case turn:lanes=* tag is redundant, just specify lanes=3 or real number of lanes

  • turn:lanes=none|none;slight_right - isn't valid combination - "there are no turn indications" on the rightmost lane. Instead, must be used (based on

  • using *right | *left values

    • turn:lanes=left|none|none or turn:lanes=||right or turn:lanes=merge_to_right|| or turn:lanes=left|left;through|none|slight_right|right|right- 👍

    • turn:lanes=|right|left| or turn:lanes=none|right|left|through or turn:lanes=none|left|none- 👎 lanes that go in one direction should not cross with each other

  • using reverse value

  • reverse (u-turn) have to be on the leftmost lane for right-hand traffic or on the rightmost lane for right-hand


to be continued …

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