[Tagging] maxspeed=signals

Peter Wendorff wendorff at uni-paderborn.de
Tue Jun 26 14:02:30 BST 2012


Am 26.06.2012 14:41, schrieb Martin Vonwald:
> 2012/6/26 Philip Barnes <phil at trigpoint.me.uk>:
>> Do we need a separate tag such as limit = variable, maxspeed = 70mph. At
>> present there is a note about active traffic management but I assume is
>> ignored by routers.
> Actually I think we do need a different tagging and also some
> different interpretation of the maxspeed tag itself:
> * First of all the maxspeed key should always contain the maximum
> allowed speed - even if it may vary. And it should always be a number.
> The only exception should be "no" for the cases where there is no
> legal speed limit. So IMO "signals" should be deprecated (currently
> used about 4000 times -> 0.18%)
I would prefer to allow (not require) an additional unit information 
(mph, km/h), simply to encourage data consumers to deal with them as 
they are usually added by users.
On the other hand no data consumer can be sure about a (global) default 
unit if there's no unit given.
> * A different tag should be used if the speed limit is somehow
> managed, maybe maxspeed:managed=yes or something similar.
>
> Why do I think that maxspeed=signals is a bad idea? Because it doesn't
> carry a lot of useful information. The speed limit is especially
> important to routing applications. For such an application
> maxspeed=signals is no information at all and it might fall back to
> the country-specific default limit - and this may (and will quite
> often) be wrong.
But what is NOT wrong?
maxspeed is the maximum allowed speed limit.
If there's a signal controlled, variable maxspeed limit, this is usually 
lower than the national default, as it's used to calm down traffic in 
rush hours and whenever it get's dangerous to drive fast.
Therefore I don't know any of these controls, that usually shows higher 
maxspeeds than the default.
It follows, that such a fallback is definitively not wrong.

What is "the usual" traffic?
In Germany the ones I know often are "unlimited" - meaning national 
default - at night (between 23:00 and 5:00 a.m for example), where 
there's not much traffic, and sometimes 30km/h during rush hours.
So what do you want to put in here?
The national default? well, that's possible with the current scheme. 
It's the fastest possible useful estimation, and most likely not a very 
good guess.
Adding a maxspeed=70, because that's what YOU usually see there, driving 
along everytime e.g. at 13:00, outside the rush hour?
Adding a maxpeed=5, because you're someone driving along in the rush 
hours every day?

Nothing is a good guess for everybody, and I don't think a time schedule 
for USUAL speed limits is a giood idea.

That's why I think, maxspeed=signals should be enhanced by some kind of 
default maxspeed limit if and only if there are non-signal default 
traffic signs with maxspeed lower than the default.

regards
Peter



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