[Tagging] Conditional restrictions accepted – turn restrictions ahead?

Ole Nielsen on-osm at xs4all.nl
Tue Oct 16 18:19:13 GMT 2012

I don't think we need to make it complicated. The Conditional 
Restrictions syntax is a bit overkill here. The restriction type is 
already known (type=restriction), so is the value 
(restriction=no_left_turn). What is left is just the condition (plus 
eventually a transport mode).

I already mentioned the following proposal on the talk page 

* condition=<condition>
* condition:<transportation_mode>=<condition>
(<condition> uses the condition values from Conditional Restrictions)

The need for the transportation mode variant will like be small as 
restriction:<transportation mode>=* should already cover this.

In my opinion there are no reasons to make it more complicated than 
that. It is backward compatible and easy to understand by mappers.

It would deprecate "hour_on", "hour_off" etc. I believe it may be better 
to keep "except" but I would like to see real-world examples of 
conditional exceptions before adapting a Conditional Restrictions like 
syntax for that key (is your example 3 real?).

Ole / polderrunner

On 16/10/2012 17:45, Rob Nickerson wrote:
> Hi Eckhart,
> Your right, voting has come to an end for the Conditional Restrictions
> proposal, which was approved. A statement was not made on this list as
> Ole and I are working on how best to write the feature page so that some
> of the concerns raised (about complexity / difficulty to understand) are
> reduced as much as possible.
> Like Martin, I'm not hugely convinced about the need for complicated
> turn restrictions (most of the restrictions will be on the road and the
> detail on the turn sign will simply be advanced warning for the driver).
> Having said that, you have provided a few examples so I have looked into it:
>    1. Currently we tag a no left turn restriction using "restriction =
> no_left_turn".
>    2. If we want this to apply only to HGVs then the key is changed so
> that it become "restriction:hgv =no_left_turn".
> To draw the comparison with "Conditional Restrictions" the above tags
> cover of <restriction type>, <transportation mode> and the tag value.
> There is no need to specify <direction> as this is already captured in
> the relation (from, via, to). Therefore the only part left to add is the
> condition. At the moment there are 2 ways to do this
>    3. Using "except = *" (where * is a vehicle type). e.g. except = bicycle
>    4. Using day on, day off, hour on, hour off
> In summary we already have both "applies" type tags (1, 2 and 4) and
> "except" type tags (3, and the inverse of 4!). My gut instinct is that
> adding an "applies = *" tag would further complicate the issue.
> In conclusion I would be in favour of adding the conditions directly to
> the restriction or except tag (depending on how the road sign is
> written). Yes this breaks backward compatibility but there are a lot
> less turn restrictions in OSM than the other restrictions and if the
> conditions are not met then the restrictions does not apply so it
> shouldn't really be tagged anyway!
> == Some Examples ==
>   * Example 1: "no u-turn" restriction for HGVs longer than 6 metres:
>   * restriction:hgv = no_u_turn @ (length > 6)
>   * Example 2: no right turn Monday to Friday 8am to 4 pm:
>   * restriction = no_right_turn @ (Mo-Fi 08:00-16:00)
>   * Example 3: no left turn except PSV's on Monday to Friday 8am to 4 pm:
>   * restriction = no_left_turn
>   * except = psv @ (Mo-Fi 08:00-16:00)
> This then depreciates the need for day on, etc... tags which I'm not a
> fan of - I think it is better to tag what is on the sign e.g. (Mo-Fr
> 08:00-19:00).
> Happy to hear your thoughts.
> Rob
> p.s. I think it would be nice to see a few more real world examples if
> anyone has any photographs (or can remember the conditions).
> p.p.s It would be nice to know how many routing software apps are using
> these turn restriction relations.
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