I was going to make a post about exactly this shortly…
In all of Queensland, u-turns at signal controlled intersections are prohibited by default, except if explicitly permitted with a “u-turn permitted” sign. This raises two issues: a. How to specify that regional legislation b. How to map u-turn permitted signs I would think that a) could be solved by a similar approach as used here: https://github.com/osmlab/osm-planning/issues/5 That is, use the same structure as is used for ELI and OCI and put that into a git repository. The exact format of how to specify different local rules would still need to be worked out. For b) I would propose that we look into adopting something like a type=permission relation, following a similar schema as type=restriction relations. Looking in overpass: https://overpass-turbo.eu/s/xBb There are currently only 8 type=permission relations, which seem to have been created by a single user in a single small area. They are already following the general schema of restriction relations (from, via, to members, and a permission=* key that describes what in particular is permitted). The 8 already existing ones are all permission=on_red_right_turn which means that it is allowed to turn right, even if the traffic signal is red (on the ground represented by a fixed green arrow sign beside the red light of the traffic signal: https://de.wikipedia.org/wiki/Gr%C3%BCnpfeil ). This schema could be easily extended to define permission=u_turn_permitted relations in queensland and other locations where u-turns are prohibited by default, but a u-turn permitted sign is present. The reason why I was going to make a post about this anyway was that https://www.openstreetmap.org/user/shawat94/ is currently busy adding 100’s of no_u_turn restrictions (4 per intersection) to all signal controlled intersections he can find... And while that is currently the only way to make the router behave, it runs the risk that any “u-turn permitted signs” that are present might get overlooked when 100’s of these are added in bulk. And adding in the end 100000’s of no_u_turn restrictions all over queensland seems a very poor plan in the long term. From: Paul Johnson <ba...@ursamundi.org> Sent: Thursday, 5 April 2018 13:16 To: Tag discussion, strategy and related tools <tagging@openstreetmap.org> Subject: [Tagging] Tagging turn restriction defaults What would be the best way to handle setting unusual defaults on a regional basis? For example, all of the City of Tulsa and State of Oregon prohibit U-turns at traffic lights. How would one tag for this, and the inverse, tagging where such a turn is allowed by a sign? Most complicated example I can think of is one intersection I remember is at https://www.openstreetmap.org/node/4597658691 and it's immediately adjacent companion for the other carriageway just south. U-turns are banned in Oregon at traffic lights, but facing Canyon Road eastbound and westbound is a sign that says "U Turn OK, CARS ONLY". Northbound and southbound traffic cannot U-turn at the light. So there would need to be an exception for motorcars coming from the east or west to allow a U-turn and a statewide regional default to deny U-turns at lights for all modes.
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