[Tagging] Conditional restrictions accepted – turn restrictions ahead?

Rob Nickerson rob.j.nickerson at gmail.com
Tue Oct 16 15:45:26 GMT 2012


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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