[Tagging] Turn Restriction usage

phil at trigpoint.me.uk phil at trigpoint.me.uk
Wed Apr 11 15:22:50 BST 2012


I found a similar problem with u-turns while investigating a mapdust bug.
http://map.project-osrm.org/hC

Not wrong, u turns are allowed for vehicles under 7.5 tonnes, but not sensible either. 

My commercial satnav told me to do a u turn here, http://bit.ly/HBOoJv, I didn't.

Phil


On 11/04/2012 14:42 Simone Saviolo wrote:

2012/4/11 Ross Scanlon <info at 4x4falcon.com>:
>>> No.  The router should know not to do this. Likewise as below the router
>>> should not make u turns at traffic lights.
>>
>>
>> Based on what? How does the router know that the two ways are two
>> carriageways of a single road? Couldn't they be a straight road, that
>> becomes a oneway street at a certain point, and at that point a
>> junction brings to a oneway secondary road?
>
>
> The name of the way, the fact that you are turning > 180 degrees on the same
> way.

I don't agree.

First, if you're on the same way, you're not turning, but going
straight and following the road. In the case of the OP, I expect to
see three ways, two of which tagged oneway=yes.

Second, if you turn more than 180 degrees, you're hopefully going on a
bridge ;-)

Third, think of a situation like this: http://osm.org/go/0CKuMhs89-
Suppose that the tertiary has to be split at the junction for any
reason (a relation needs only a part of it, or the surface changes, or
the incline changes, whatever). Also suppose that the tertiary is
oneway=yes. You would end up with two ways with the same name, both
oneway=yes, with an acute angle between them and a third way exiting
from the junction. Would you, as a router, ban the prosecution on the
tertiary?

Regards,

Simone

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