[Routing] Leave motorway, turn onto track

[David Lynch]

This needs to be set with turn restrictions or permissions on the
track. There are places in the western US where there are legal turns
directly from a motorway onto what would probably best be classified
as tracks, including a few actual crossroads, such as at
http://www.openstreetmap.org/?lat=31.1514&lon=-105.2699&zoom=14

On Fri, Oct 10, 2008 at 09:33, Jon Bright <jon at siliconcircus.com> wrote:
> Hi Frederik,
>
> Frederik Ramm wrote:
>>
>> I wonder if it would nevertheless make sense for routing engines to
>> implicitly disallow leaving a motorway on anything else than a
>> motorway_link (or at least not on something as small as a track).
>
> You'd certainly want to allow leaving a motorway onto trunk, primary and
> secondary.  Near where I live, the A46 (motorway) ends and turns into
> the B326 (primary):
>
> http://www.informationfreeway.org/?lat=51.31285458075313&lon=7.27426070665261&zoom=17&layers=B0000F000F
>
> Something similar happens east of London, where the M25 (motorway)
> becomes the A282 (trunk) for the Dartford river crossing:
>
> http://www.informationfreeway.org/?lat=51.48429693501172&lon=0.2717440463221352&zoom=15&layers=B0000F000F
>
> An example with secondary would be this bit of the A44:
>
> http://www.informationfreeway.org/?lat=51.32945959272296&lon=7.016253712974789&zoom=17&layers=B0000F000F
>
> My suggestion for a solution would be to explicitly exclude "track".  In
> theory, as you say, even this shouldn't be necessary.  I don't think you
> even need turn restrictions - as far as I'm aware, pretty much every
> such track has access restrictions preventing its use as an exit.  But
> in practice, not everyone will have tagged everything perfectly, so
> excluding "track" (and maybe also "unclassified") seems like a
> reasonable compromise.
>
> (A more complicated and computationally intensive way of doing this
> would be to disallow turns where the turn angle is greater than 45
> degrees from the motorway and the motorway itself continues.  But I
> think the better way to deal with that would be to analyse the OSM data
> for such cases, produce a list and have "gardeners" enter appropriate
> access or turn restrictions.)
>
> Another case you might want to think about while looking at this is
> places like:
>
> http://www.informationfreeway.org/?lat=51.94166322328894&lon=7.553746825469445&zoom=15&layers=B0000F000F
>
> This is a normal rest stop on the motorway (between Münster-Süd and
> Münster-Nord.  The quickest way to reach some parts of Münster is to
> leave the motorway at the rest stop, take the road leading off parallel
> to the motorway and then join the K5.  But it's also illegal to do so.
>
> Refusing ever to turn from a motorway onto highway=service might
> therefore also be appropriate.
>
> Jon
>
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-- 
David J. Lynch
djlynch at gmail.com