Proposed features/traffic speed

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traffic_speed
Status: Proposed (under way)
Proposed by: Spod
Tagging: type=traffic_speed
Applies to: relation
Definition: Traffic speed at a specified time
Rendered as: hidden
Drafted on: 2010-10-04

Proposal

To provide traffic speed data, so that more accurate time estimations for routes can be calculated, so that routing algorithms can return better routes.

To be used, for example, on roads with "rush hours", where the traffic speed can be significantly lower than the applicable legal maximum speed.

Applies to roads (and other ways) where, at times, the traffic speed can be consistently measured to be significantly different to the value of Key:maxspeed.

Rationale

When the real traffic speed is significantly different from the maxspeed, the routes selected by routing algorithms are bad. This can be improved by providing real traffic speeds.

Usage

It is recommended that the traffic_speed relation should only be used when the speed is:

  • Significantly different to the legal maximum speed (to reduce the need to add the relation to all roads)
  • Regularly and consistently measurable (so the data is useful for routing)

It should not be used for:

  • Roads affected by "one-off" events like soccer matches or music festivals, where the effect on traffic is likely to be irregular and unpredictable. For such events a (probably) separate "avoid this area at this day/time" tag would be more appropriate, which could affect roads contained within a more general area.

Tags and Values

Key Required Value Discussion
type required traffic_speed
<transport-mode-list> optional <time-span> <speed>;...
<transport-mode-list>:<direction> optional <time-span> <speed>;...

Where:

  • <transport-mode-list> is a semicolon-separated list of the relevant modes transport from Key:vehicle (e.g. "motorcar", "bus", "bicycle", "vehicle", "bus;taxi")
  • <direction> is one of:
    • forward (the speed applies to the forward direction of the way)
    • backward (the speed applies to the backward direction of the way)
  • <time-span> a time span as in Key:opening_hours (e.g. "Mo-Fr 16:30-18:30")
  • <speed> is a speed value as in Key:maxspeed (e.g. "5", "8mph"). The average time when travelling along the way i.e. the distance divided by the time, in hours, to travel along the way.
  • If a list of speed and time-spans is required, each speed and time-span can be separated by semicolons. e.g. "bus=Mo-Fr 16:30-18:00 10mph;Mo-Fr 18:00-18:30 20mph"

Examples of usage

  • A road, which has a bus and taxi lane, and which is affected by "rush hours" in opposite directions on weekday mornings and evenings could be tagged with a traffic_speed relation containing:
    • motorcar:forward=Mo-Fr 08:30-9:30 8mph
    • bus;taxi:forward=Mo-Fr 08:30-09:30 40mph
    • motorcar:backward=Mo-Fr 16:30-18:30 8mph
    • bus;taxi:backward=Mo-Fr 16:30-18:30 40mph

Applies to

  • Ways

Interpretation by routing algorithms

Expected behaviour for routing algorithms:

  • When estimating route times for a route and mode of transport, use any relevant traffic_speed tag data.
  • In the absence of a traffic_speed tag, or if the traffic_speed tags do not apply to the mode of transport, use the 'default' speed (whether that is from Key:maxspeed or some other - hopefully better! - mechanism).
  • It is expected that routing algorithms should know that for certain classes of roads in certain countries/areas, (e.g. UK cities) that the average traffic speed is "always" less than the legal maximum (because of slower traffic causing delays etc). Therefore, we do not need to add the traffic_speed relation to "ordinary" roads.

Rendering

Normally not rendered. Could be rendered on a "rush hour" map.

Comments

Use the Talk:Proposed_features/traffic_speed page.

See also