[Routing] Default speed limits / built-up areas (was: Re: generalized routing format - pre-computation)

[Sascha Silbe]

On Mon, Oct 20, 2008 at 10:31:35PM +0200, Nic Roets wrote:

> During rebuild, gosmore only mmaps the wayType data which is roughly 
> 1GB.
> During one stage, it iterates through the node data and update the 
> wayTypes
> they point to so that bounding boxes can be computed.
OK, so you don't index by location currently (since that would need 
bounding boxes)? How does your geocoder work? I.e. how does it find a 
given street inside a given town?


> I don't believe that writing software for adjusting speeds for 
> built-up
> places is worth all the effort. Reasons :
It may be a misunderstanding because of my choice of words (I'm not a 
native speaker) or there may be countries where it works differently. 
Since both are important for me to sort out, I'll explain how it works 
in Germany:

Each time you enter a town (or village or whatever), there's a yellow 
sign (StVO sign number 310 [1]). Exactly at the location of these signs 
the defaults change from 100km/h to 50km/h (for cars). This is regulated 
by law (Straßenverkehrsordnung (StVO) § 3 (3) [2])
The area delimited by these signs is called "Geschlossene Ortschaft" 
[3], roughly translated it would be "closed (=delimited) place 
(village)".

Mapping these signs
a) is mapping what's on the ground
b) is important for speed calculation during routing (see below)
c) needs to be done with different tags since it's completely different 
from
     - landuse=residential ("there are some residential buildings")
     - place=town/... ("addresses within this polygon are part of town 
XYZ")
     - boundary=administrative ("this land (town+fields) is administered 
by town XYZ")

Not having these polygons (and most often not even one of the others) is 
the number one cause for "bad" (=suboptimal) routes I've encountered. 
The router chooses the streets _through_ the city instead of _around_ it 
(most places with significant non-local traffic have "bypass roads" 
(Ortsumgehungsstraßen) that lead around town). As both streets are of 
equal quality (e.g. both are primary and 2 lanes per direction), it's 
only natural for the router to do so.

  From my visits to Swiss and Austria, I had the impression it works 
very similar there (defaults changing at the town sign). So there's 
quite a large number of users affected by this (well, even if it were 
just Germany, it'd suffice :) ).

There are
a) other things besides default speed limits that change at said signs 
(e.g. use right lane vs. free choice of lane)
b) other signs and facts that affect default speed limits (motorways, 
divided highway, ...)


How does it work in other countries? Are there different defaults and 
where do they change? What "prevents" you from driving as fast inside a 
town as you would outside?


[1] http://de.wikipedia.org/wiki/Bild:Zeichen_310.svg
[2] http://bundesrecht.juris.de/stvo/__3.html
[3] http://de.wikipedia.org/wiki/Geschlossene_Ortschaft


CU Sascha

-- 
http://sascha.silbe.org/
http://www.infra-silbe.de/
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