User:Gauß/Turn Restrictions

Problems with the current turn restriction relation

1. It isn't possible to visualize all traffic signs that are in use. Only a small subset is available, so that other traffic signs are replaced with equivalents. Some of those equivalents are unusual in certain countries. Example: instead of .
2. It isn't possible to fix the above problem by replacing some of those currently allowed traffic signs with local variants, because the meaning isn't exactly the same. For example: only_straight_on_or_right_turn (which doesn't exist) is usually expressed as no_left_turn which is equivalent at conventional crossings but not at T-crossings:

3. It isn't possible to express country specific styles of traffic signs, like for example different arrow forms or different color sets. (Brazil, Sweden, etc.)
Examples:
instead of
instead of
instead of
instead of
4. It isn't always possible to express turn restrictions in a single relation. In many cases several turn restriction relations are combined. All traffic signs of those relations are supposed to be rendered.
5. Another missing class of turn restrictions:

Some traffic signs

	Traffic sign	Turn restriction	Remark
1		only_straight_on_or_right_turn	Germany, Italy, Japan, The Netherlands, Russia
2 a		no_left_turn	Australia, Brazil, France, Ireland, Poland, Russia, Spain, Switzerland, UK, US (R3-2; R3-18 combined with no U-turn)
2 b		no_left_turn	Sweden
3		only_straight_on_or_left_turn	Germany, Italy, Japan, The Netherlands, Russia
4		no_right_turn	Australia, Brazil, France, Ireland, Spain, Poland, Russia, Switzerland, UK, US (R3-1)
5 a		only_left_turn_or_right_turn	Germany, Japan, The Netherlands (RVV 1990, sign D7), Poland, Russia, Switzerland, Israel, Italy
5 b		no_straight_on	Brazil, Ireland, US (UK and France never use such signs - you would usually see adjacent left-turn-only and right-turn-only signs in such a situation; see 5 a)
6 a		no_u_turn	Germany, France, Japan, Spain, Poland, Switzerland, Brazil, The Netherlands, US (R3-4), Israel, Russia
6 b		no_u_turn	Australia, United Kingdom
7		only_u_turn	Austria
8 a		only_right_turn	typically on the approach to a junction In the US, a white rectangular sign is used for this situation and for the case where one lane on a multi-lane road must turn (R3-5R)
8 b		only_right_turn	typically at the junction In the US, a white rectangular sign is used for this situation and for the case where one lane on a multi-lane road must turn (R3-5R)
8 c		only_right_turn	Brazil
9 a		only_left_turn	typically on the approach to a junction In the US, a white rectangular sign is used for this situation and for the case where one lane on a multi-lane road must turn (R3-5L)
9 b		only_left_turn	typically at the junction In the US, a white rectangular sign is used for this situation and for the case where one lane on a multi-lane road must turn (R3-5L)
10		only_straight_on	Used in Russia and in the United Kingdom; usually seen just before a junction or on the approach to a junction In the US you'll see the text "NO TURNS" in a white square (R3-3; R3-5a is usually used only in the case where one lane on a multi-lane road must turn)
11	File:3.1.svg	no_entry	Used for not one-way roads, where entering across some point (member node with role via) is prohibited. Relation can have several from members and one to member.
12	File:3.1.svg	no_exit	Used for not one-way roads, where exiting across some point (member node with role via) is prohibited. Relation can have one from member and several to members.

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