Proposal:Junction

It has been proposed that this page or section be merged with Relations/Proposed/Junctions. (Discuss)

It has been proposed that this page or section be merged with Proposed features/Set of Traffic Signals. (Discuss)

Junctions
Proposal status:	Draft (under way)
Proposed by:	Ivansanchez
Tagging:	`junction=*` Data item
Applies to:	linear
Definition:	Complex road junctions, and parts of those complex junctions
Statistics:
Rendered as:	N/A (applies mostly to routing)
Draft started:	2008-06-30
RFC start:	*
Vote start:	*
Vote end:	*

Rationale

I'm tired of only being able to use "roundabout" for the "junction" tag. There is much room for improvement. Also, seeing the overcomplicated types of road junctions in existence, it makes sense to build on top of that.

Also, adding more semantic detail to complex junctions should enable router software to build better directions.

This applies to ways that already have a highway=* tag.

Values

I'll make two groups of junctions: junction elements and complete junctions.

Junction element tags are to be applied to individual ways; complete junction tags are to be applied to relations encompassing all the junction elements that are connected.

Junction elements

Tag	Description	Picture(s)	Aerial image(s)
Either `junction=slip` or `junction=ramp`	A slip (or slipway) is any piece of road that connects road A with road B, not being part of neither of those.	(Add pictures)	(Add images)
`junction=traffic_circle`	A traffic circle is a section of road in which the traffic describes a circle (d'oh!). It is different from a roundabout in the sense that a traffic circle is generic, and a roundabout has certain rules regarding vehicle priority. Traffic circles in which the traffic priority scheme is different from a roundabout should be tagged as traffic circles. (Image shows "give way" signals, not direction arrows)		Note the white lines in the pavement, giving priority to vehicles entering the intersection
`junction=roundabout`; implies `junction=traffic_circle`	A roundabout is a subtype of traffic circle, in which the vehicles inside it have preference over the vehicles about to enter the roundabout. Please note how the "give way" signals are located at the entrance to the roundabout. (Image shows "give way" signals, not direction arrows)		(Add images)
`junction=raindrop`; implies `junction=roundabout`	A raindrop is an uncomplete roundabout, in which it is impossible to make a full circle. The shape of the traffic isle inside the raindrop gives it its name.	(Add pictures)
`junction=braid` or `junction=weave`; implies `junction=slip`	A braid is a short section of one-way road where traffic "weaves"; two roads join into the braid (in an inverted "Y" shape), and then the braid splits into another two roads (in a "Y" shape). Usually, the traffic coming from the left will depart to the right, and vice versa (hence the term). (Note: In USA engineering terms, "braiding" is an arrangement, typically involving at least one bridge, specifically to avoid a "weave" configuration as described here.)
`junction=onramp`; implies `junction=slip`	An on-ramp is a one-way slipway that connects a non-motorway to a motorway. Residents in USA, replace the term "motorway" by "freeway".		(Add images)
`junction=offramp`; implies `junction=slip`	The opposite of an on-ramp, an off-ramp is a one-way slipway that connects a motorway to a non-motorway.		(Add images)
`junction=racket`; implies `junction=slip`	A racket (from the spanish "raqueta") is a slipway in a same-level crossing that allows vehicles to reduce speed and stop prior to crossing the road transversally. A racket is always exterior to the crossing, and always has a "stop" or "give way" traffic signal. (In USA, especially New Jersey, this is called a "jughandle".) The term "racket" or "perform a racket (maneuver)" also applies to any junction where the driver has to leave the road to the exterior, in order to cross the road. E.g. when turning left on a spanish cut roundabout.
`junction=leaf`; implies `junction=slip`	You know what a cloverleaf exchange is, right? A leaf is the staple element of a cloverleaf - a sliproad that describes a 270 degree turn.		(Add images)

Complex junction relation

As said before complex junctions will be mapped as a relation. Here is the structure suggested:

Tags:

Key	Value	Discussion
type	junction
junction	See table	link is for clover leaf and similar type junctions; just omit this tag for junctions like cross-roads and simple single-bridge motorway junctions (unless someone can suggest a vocabulary for them)
grade_separated	yes	if it is grade separated (perhaps this can be used to imply layering and bridges without having to individually model each?)
name	a name	if the junction has a name (e.g. "Charlie Brown's Roundabout")
ref	a reference	if the junction has a number (e.g. junction 10 on a motorways would be "10")

Members:

Way or Node	Role	Recurrence?	Discussion
	(blank)	one or more	the ways and/or nodes comprising the junction (a typical grade separated motorway junction would combine ways, but a simple cross roads only has a node comprising it. A single carriageway crossing a dual carriageway might include the two nodes and the link between the carriageways in the junction.
	location_hint	optionally one	a hint to a renderer as to where a good place to put the the junction number or name on the map

Complex junctions

Tag	Description	Picture(s)	Aerial image(s)
`junction=exchange` or `junction=interchange` or `junction=link`	A generic name for complex junctions that don't have any other narrower description.	(Add pictures)	(Add images)
`junction=cloverleaf`; implies `junction=exchange`	You already know what a cloverleaf is. Two motorways (or freeways), four external slipways, four leaves.
`junction=trumpet`; implies `junction=exchange`	You also know what a trumpet is. Two motorways (or freeways), one ends at the other.		(Add image)
`junction=parclo` or `junction=partial cloverleaf`; implies `junction=exchange`	A cloverleaf exchange that has fewer than 4 leaves.		(Add images)
`junction=stack`; implies `junction=exchange`	A four-way exchange with no leaves or weaving, and paired (simmetric) slipway bridges (or even tunnels).		(Add images)
`junction=diamond`; implies `junction=exchange`	One motorway; two on-ramps; two off-ramps. The ramps merge at a non-motorway on a bridge or tunnel.		(Add images)
`junction=dumbbell`; implies `junction=exchange`	A diamond exchange in which the crossings between the ramps and the non-motorway road are replaced with two roundabouts; there is a single bridge or tunnel connecting the two roundabouts.
`junction=roundabout exchange`; implies `junction=exchange`	A diamond exchange in which the crossings between the ramps and the non-motorway road are replaced with one roundabout. This (large) roundabout spans over (or under) the motorway by means of two separated bridges (or tunnels). This roundabout may be represented as a relation, encompassing the bridge and the non-bridge segments.		Note that in this particular exchange there is only one bridge that spans under all the roundabout
`junction=cut roundabout` or `junction=split roundabout`; implies `junction=exchange`	A roundabout that is cut down by the middle by one of the incoming roads. The name is a literal translation of the spanish "Rotonda partida", which can translate to either "cut roundabout" or "split roundabout". Please note that the blue line in one of the images is also a "racket maneuver" mentioned earlier. This maneuver is the only (legal) way for the blue car to turn left; there is an implicit turn restriction that prevents it from turning left in the main road.		Legal maneouvers in a cut roundabout Please note how the "racing line" effect on the road color occurs on legal turns.