Am 26.06.2012 14:41, schrieb Martin Vonwald:
2012/6/26 Philip Barnes <p...@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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