[Talk-us] Prima Facie Speed Limits

Tod Fitch tod at fitchdesign.com
Tue Sep 9 19:38:27 UTC 2014


Historical and live speed profiles are pretty much required for trip planning in congested urban areas, but for those of us who drive close to the speed limit and make long trips on relatively uncrowded rural freeways, travel time estimates based on posted (or prima facie) speeds are a good approximation to reality. I travel between northern California and southern Arizona a lot. The distance is about 1,300 kilometers and only a small fraction of that is congested urban freeways (especially if I decide, as I usually do, to avoid Los Angeles). OsmAnd with its knowledge of actual posted speed limits (many entered by me) does a very good job at predicting my arrival time.

On Sep 9, 2014, at 11:48 AM, Martijn van Exel wrote:

> There's a functional difference between speed limits and the actual speed driven. For ETA prediction, speed limit data is not all that useful - detailed historical and live speed profiles are. That is not data that is in OSM (or should be). The speed limits are mostly useful for alerting drivers they may be driving too fast. For a system like that to be feasible you will need comprehensive posted speed limit coverage, which OSM currently does not have.
> 
> Martijn
> 




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