roundabouts

FvGordon · 2017-01-31T11:26:16.000Z

What is the main difference between a roundabout and a gyratory?

Can I see the difference in the satellite background image?

Does a gyratory has a different traffic sign than a roundabout when entering it with a car (other than the three white arrows on blue background)?

Franz

gegeb · 2017-01-31T12:08:52.000Z

If you examine the tags for example regarding the “Place de la Porte de Saint Cloud” in Paris you will see that in the note it is mentioned “Not a roundabout pas un giratoire” because historically it has been done like that; so the only way to consider a roundabout that isn’t a gyratory is to use as indicated in the OSM data base “junction=circular”.

TZorn · 2017-01-31T14:17:59.000Z

I’m still stuck with your initial question. Could you please explain what a “gyratory” is or is not, opposed to a “roundabout”. I am not familiar with the term.

hadw · 2017-01-31T21:22:22.000Z

I think there may be country specific issues here. In the UK, junction=roundabout SHOULD NOT be used for gyratory systems.

escada · 2017-02-01T07:20:56.000Z

@FvGordon: according to wikipedia https://en.wikipedia.org/wiki/Roundabout#Gyratory_system

The term “gyratory” is sometimes used in the United Kingdom for a large circular intersection with non-standard lane markings or priorities, or when buildings occupy the central island.[52]

turepalsson · 2017-02-01T07:48:19.000Z

There are (at least!) two kinds of places where traffic goes in a circle: Those that have special signage (in Europe, this is typically a circular blue sign with white arrows going in a circle) that assigns priority to traffic already in the circle, and those that are just circular roads with no special rules, meaning that the traffic entering the circle has priority because it is coming from the right (or left, in the UK and a few other places). In OSM, junction=roundabout is reserved for the first kind, with traffic already in the circle having priority.

There is room for linguistic confusion here. In France, I believe that a “carrefour giratoire” refers to the first type (junction=roundabout in OSM) while apparently the British use “gyratory system” to mean something else. In everyday English, the terms “roundabout”, “traffic circle”, “gyratory” and probably a few others seem to be thrown around with little respect for legal definitions, and I suspect that the same is true in French (giratoire, rond-point, …) (it certainly is in Swedish, though luckily, the second type is scarce here).

So I agree with TZorn — this thread needs definitions!

Edit: A “the” should have been a “be”.

gegeb · 2017-02-01T12:58:43.000Z

I think that the soluion for a roundabout in every sens, would be to solve any ambiguity, to have in OSM “junction=roundabout”,whatever the giratory systems or circular roads.
Remark:this proposal has been refused by an OSM member in charge of the database. This leads on site to a discrepancy between the way to follow and the voice guidance for circular roads that consequently are treated as normal roads when entering in a roundabout in every sens.

SK53 · 2017-02-01T13:32:29.000Z

The general rule is to use british english (in this case for good reasons as usage even within the US varies), Beware of false friends (faux amis) :

Roundabout: a topologically circular path where traffic on the path has priority over traffic entering the path. As others have said in Europe this is marked by a standard sign. Entry points should have give way (yield) markings: in Britain dashed white lines. In the US these are usually called modern roundabouts.

Gyratory: a oneway system which is also a topologically circular path, but where traffic on the path does not necessarily have priority. The best known one in the UK is the Hangar Lane Gyratory System. Usually access and priorities are controlled by traffic signals, and thus most entries will have a stop markings. I suspect that junction=gyratory should be reserved for places where the path is signal controlled. NOTE: Many roundabouts in Britain now have traffic signals controlling flow both on to the path and within the path. These are still generally tagged as roundabouts even though they are properly gyratory systems. I suspect in the event of failure of the lights British drivers would still treat them as roundabouts.

Other circular roads with different properties with respect to priorities and management of access should not receive one of the above tags. I suspect that using junction=traffic_circle would be a potentially suitable tag. The historic exemplar for me would be the Rond Point d’Etoile (Arc de Triomphe) in Paris. The example given very much fits into this category.

The problem is one of working out how to manage the differences for data consumers. All three types can validly have routes described as " take the 3rd exit", but have very different properties for things like lane tags or calculation of delay times.

One other useful clue as to whether it’s valid to tag something as a roundabout or not is the presence of bus stops. These rotary junctions are usually significant interchange locations for buses. Allowing any vehicle to stop goes against the basic principle of roundabouts. So bus stops located on the actual junction suggest that junction=roundabout is inappropriate.

gegeb · 2017-02-01T14:34:08.000Z

traffic_circle is not currently in the possibilities for junction in the database but junction=circular is in it. Could we use it?

hadw · 2017-02-01T20:57:11.000Z

I don’t understand what you mean by “in the database”. There is no database of valid tags.

gegeb · 2017-02-01T21:43:24.000Z

When you want to modify for example a “roundabout” in OSM, several tags are available such as:
junction=roundabout
junction=gyratory
junction=circular
and others.

hadw · 2017-02-02T08:28:40.000Z

I think you are confusing a particular editor with OSM. I can add any lexically valid key with any lexically valid value to a road or junction. Even iD will allow you to do that, although it is, maybe, less obvious than JOSM.