[Tagging] maxspeed=signals

Eckhart Wörner ewoerner at kde.org
Tue Jun 26 18:42:27 BST 2012

Hi Martin,

Am Dienstag, 26. Juni 2012, 12:43:10 schrieb Martin Vonwald:
> The tag maxspeed=signals doesn't carry any useful information in this
> situation. If I tag those speed limits with this tag we completely
> lose the information that on this part(s) of the motorway one usually
> can drive 100km/h and not 130km/h. So is this tag really a good idea
> in this case? I understand that this might be necessary on roads where
> the speed limit changes frequently, e.g. at some specific times.

here's another example: motorway A 100 in Berlin has maxspeed signs that might change between 80 and 60, depending on traffic conditions [1], and is therefore tagged maxspeed=signals. If route calculation just takes the default maxspeed for motorways, it will end up with maxspeed=none, which is way off. Also, a routing program could warn the driver if he's going more than 80.

First of all, the problems we're actually trying to solve:
a. Route calculation needs a tentative maxspeed on roads with dynamic speed limits
b. Speed warning needs an absolute maxspeed on roads with dynamic speed limits to prevent the driver from speeding when possible (it is not acceptable if the software warns on a limit that's too low)

I believe the difference between tentative maxspeed and absolute maxspeed is small enough to justify that we just assume tentative maxspeed = absolute maxspeed.

Problems we should avoid:
a. Static speed information that depends on conditions known to a routing software or the driver (time of day, weather, children present). They are covered by the extended conditions proposal.
b. "Dynamic" speed information that is in fact not dynamic (speed signs that are programmed to show specific speed signs at specific times). They are also covered by the extended conditions proposal. (Correctly identifying a "dynamic" sign as static can be quite difficult, though.)


[1] http://goo.gl/maps/uyQz

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