[Talk-GB] No U-turn on a long stretch of road

Robert Skedgell rob at hubris.org.uk
Sat Dec 5 16:13:43 UTC 2020

This probably won't help routers much, but you could at least tag the
positions of the signs as nodes on the highway with
traffic_sign=GB:614 + direction=forward|backward

On 05/12/2020 14:27, Edward Bainton wrote:
> Sorry I should have made clear 
> Rather than seeking to capture a subjective jmt in the map, I'm trying
> to capture "no U-turn" signs that are shopping this long stretch, . 
> I agree a driver should use their discretion. Equally where it's
> actually prohibited do we want to capture that?
> On Sat, 5 Dec 2020, 12:57 David Woolley, <forums at david-woolley.me.uk
> <mailto:forums at david-woolley.me.uk>> wrote:
>     On 05/12/2020 12:39, Edward Bainton wrote:
>     > Any established tagging system?
>     >
>     > The turn restriction wiki
>     > <https://wiki.openstreetmap.org/wiki/Relation:restriction
>     <https://wiki.openstreetmap.org/wiki/Relation:restriction>> envisages
>     > turn restrictions at junctions only; my case is along the length of a
>     > major road (~3km). There's no barrier to prevent it, but presumably
>     > routing engines ought to know that route correction after a wrong
>     turn
>     > will have to wait until the next roundabout.
>     >
>     That's a subjective judgement, so would be tagging for the renderer.
>     The renderer (in this case a router) should be using some sort of
>     heuristic like only  permitting U turns on residential or service
>     roads,
>     and giving a heavy weighting to the use of formal junctions at the the
>     expense of distance travelled.  A real human would consider actual
>     traffic levels and sight distances but they would be difficult to
>     capture on the map and time and season dependent.
>     I think No U Turn signs tend only to be used where traffic volumes or
>     junction structures, might otherwise suggest U turns were acceptable.
>     I don't think any driver (or autonomous vehicle) should be making U
>     Turns based solely on the instructions of an automated router.

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