[Talk-us] Prima Facie Speed Limits

[Martin Koppenhoefer]

2014-09-09 17:47 GMT+02:00 Martijn van Exel <m at rtijn.org>:

> I'm of the opinion that wherever the speed limit is just the default for
> that road class, it should not need to be posted at all. Any data user can
> then infer limits.



I don't know how this is handled in the US, but in Europe you will
definitely need explicit speed limits because there is no road class in OSM
that represents the needed properties. In Germany and Italy (and likely in
many other countries as well) for instance there is a distinction between
"inside settlement" and "outside settlement". Now not all residential roads
are inside a closed settlement, and not every settlement is considered a
settlement for the purpose of this law. The actual limits get set by the
city_limit signs, which do not correspond to actual settlement boundaries
but are put where the traffic planners think you should slow down (i.e.
even if we mapped places in osm in all instances as areas, this place area
would not correspond to the area with "urban" city limit).

Besides this, there is another issue: when a key in osm is missing, you
will not know if it is missing (here maxspeed), you will not know if it is
missing or if the default should apply.

Both are IMHO strong arguments to map also "default" (i.e. implicit, not
sign-posted) speed limits, while the dataconsumers (e.g. routers), will of
course need default values for road classes, especially for the cases of
missing maxspeed information.

cheers,
Martin
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