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An '''interchange''' is a road junction where two roads are connected by dedicated roadways, called '''ramps'''. The roads connected by an interchange do not intersect one another directly, and if they cross, the crossing is grade-separated.
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An '''interchange''' is a road junction where traffic can move between roads that do not intersect. The roads are connected by ramps, and if they cross, the crossing is grade-separated. They are most commonly used where one or more roads is a controlled-access highway. Complex interchanges may contain many highways and local roads meeting within small areas. Many different layouts have been developed by traffic engineers to optimize interchanges for size, complexity, traffic safety, navigation, and unimpeded traffic flow.
  
Since interchanges often involve grade-separated crossings, the [[road elevation]] of the segments becomes important. If two roads cross without connecting directly, their elevations must be different.
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This article is a sub-article of the [[Junction Style Guide]]. As such, '''this article is a style guide''' as well. Representing interchanges on the map can be exacting and difficult. The guidance on this page will help editors to create accurate and usable map versions of these interchanges. The following sections discuss the proper style for ramps, interchanges, and some common interchange designs. Note that some interchanges may be a hybrid of these basic designs where one side or quadrant of the interchange may differ from the others. Also note that since interchanges often involve grade-separated crossings, the [[road elevation]] of the segments becomes important. If two roads cross without connecting directly, their elevations must be different.
 
 
This article is a sub-article of the [[Junction Style Guide]]. As such, '''this article is a Style Guide''' as well. The following sections discuss the proper style for ramps, interchanges, and some common Interchange designs. Note that some interchanges may be a hybrid of these basic designs where one side or quadrant of the interchange may differ from the others.
 
  
 
Before reading through this article, be sure to fully understand the information in the [[Junction Style Guide]].
 
Before reading through this article, be sure to fully understand the information in the [[Junction Style Guide]].
  
== Ramps ==
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==Ramps==
  
Ramps have a very specific purpose in Waze. They are intended to connect segments of Minor Highways, Major Highways, and Freeways to roads where there are no at-grade crossings.
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Ramps have a very specific purpose in Waze. They are intended to connect segments of minor highways, major highways, and freeways to roads where there are no at-grade crossings.
  
 
The {{Ramp}} type is used extensively in interchanges for three reasons.
 
The {{Ramp}} type is used extensively in interchanges for three reasons.
* Ramp segment names are not displayed on the map. This
 
* Ramp segments have essentially no penalty, so they can be used to connect Freeways and Major Highways with each other without causing problems.
 
* Ramp segments are relatively small but show at high zoom levels, so interchanges do not distract from highways but can be seen at high speeds.
 
  
=== When to use ramps ===
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*Ramp segment names are not displayed on the map.
 +
*Ramp segments have essentially no penalty, so they can be used to connect freeways and major highways with each other without causing problems.
 +
*Ramp segments are relatively thin but show at wide zoom levels, so interchanges do not distract from highways but can be seen at high speeds.
 +
 
 +
===When to use ramps===
  
 
Use of the {{Ramp}} type is governed by the following rules:
 
Use of the {{Ramp}} type is governed by the following rules:
* [[Road types/USA]]
 
* [[At-grade connectors]]
 
  
=== Ramp geometry and complexity ===
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*[[Road types]]
 +
*[[At-grade connectors]]
 +
 
 +
==Geometry==
  
Rule #1 is still simpler is better. If there is no large distance between paths at the end of a ramp (either into or out of the ramp), a single segment connecting to a single junction node is all that is needed. The existence of a painted, concrete, or grass island is '''NOT''' enough of a reason to split a ramp into multiple ramps.
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===Exits, forks, and wayfinders===
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This section concerns the geometry of the following junctions:
  
: [[Image:Jct_ramp_no_split.png]]
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*'''exits''', which are junctions at which ''one'' outbound segment (typically a ramp) carries traffic off of a road and the other outbound segment continues the same road as the entry segment;
 +
*'''forks''', which are junctions at which ''either both or neither'' outbound segment continues the same road as the entry segment; and
 +
*'''wayfinders''', a type of exit or fork which is set up to instruct the driver to stay on the road they're already on.
  
When paths at the end of the ramp deviate significantly in distance, regardless of the existence of any type of island, then multiple ramps should be used.
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When mapping an exit or fork (or wayfinder), there is one guiding question: '''is there one clear straight-ahead path?''' That is, does one and only one outbound segment clearly continue the same path as the inbound segment?
  
: [[Image:Jct_ramp_split.png]]
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<gallery>
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File:Aheadpath2.jpg|Yes, the left path is the clear straight-ahead path—even though these are exit ramps and there is no “continuation” per se, the left path is totally straight while the right path diverges immediately.
 +
File:Aheadpath3.jpg|No, there is no clear straight-ahead path—both paths are equally straight ahead, so there is not ''one'' clear straight-ahead path.
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File:Aheadpath1.jpg|No, there is no clear straight-ahead path. This is a "typical" ramp fork.
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File:Aheadpath4.jpg|No, there is no clear straight-ahead path—both paths are equally straight ahead, so there is not ''one'' clear straight-ahead path.
 +
</gallery>
  
== Interchange types ==
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====Where there is a clear straight ahead path====
These are junctions involving the three Highway/Freeway road types - {{Minor Highway}}, {{Major Highway}}, and {{Freeway}} -- as well as their {{Ramp|Ramps}}.
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The straight ahead path should be more or less straight, with a smooth transition.
  
Specific examples of how to handle common junction types are provided in later sections.  All of those examples use the basic building blocks provided here.
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The diverging path should be configured as follows:
  
If you are unsure what road type you should use, refer to the following pages for more information.
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*First, place the first [[geometry node|geometry handle]] of the diverging segment as follows:
*[[Road_Types_(USA)|United States]]
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**on freeway exits and other similarly-configured ramps, at the '''nearest point''' to the exit from the following:
*[[How_to_label_and_name_roads_%28United_Kingdom%29#Road_types|United Kingdom]]
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***If there's no solid white line, at the gore point (or "theoretical gore", i.e., where the painted lines diverge)
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***If there's a solid white line, at its beginning
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***On a multi-lane exit, at the gore point or solid white line between the inner exit lane and the adjacent continuing lane
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***1/4 mile before the gore point, on exits with a longer solid white line
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***Halfway between the gore points of the exit and the previous exit
 +
**on at-grade connectors, at the '''gore point'''.[[File:NaturalDeparture.jpg|thumb|Use the natural departure angle for a segment with a true departure angle of at least 20°.|250x250px]]
 +
*Next, grab the node itself, where the segments meet, and adjust the geometry of the exit itself as follows:
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**If the actual path of the exit diverges from the inbound path by less than 20°, adjust the node to create a 20° departure angle. This will allow for consistent timing of exit instructions and make it easier to report closures in the Waze client.
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**If the actual path of the exit diverges immediately from the inbound path by more than 20°, adjust the node such that the exit path follows its true natural departure angle.
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*Finally, ensure that the last geometry handle before the node is at least 40 feet ahead of the node, and that the second geometry handle on the diverging path is at least 40 feet beyond the first geometry handle.
  
=== Exits ===
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[[File:ExitRampShort.jpg|900px]]
It is a basic Exit situation when a "straight" direction is obvious to a driver and navigation instructions are only needed for the non-straight direction (the exit.)  If navigation instructions are required for both directions, see the [[#Wayfinder_Segments|Wayfinder Segments]] section below.
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{{clear}}
  
==== Exit geometry ====
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====Where there is not a clear straight ahead path====
: [[Image:Jct_fwy_exit.png]] [[Image:Jct_maj_exit.png]] [[Image:Jct_min_exit.png]]
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[[File:Essentiallysymmetrical.jpg|thumb|Essentially symmetrical: yes, departure angles of outbound segments are very close (7° and 8°). At least 15°: yes (de-select any segments and select the node to check).|250px]]
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Whether both outbound paths are or neither outbound path is straight ahead:
  
To be treated as a basic Exit, the following must be true:
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*First, adjust the inbound segment geometry to follow the inbound segment's true path.
# The entering segment and one exiting segment must be one of the three Highway/Freeway types
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*Next, set the first geometry handles of both outbound segments in line with the gore point.
# The Highway/Freeway exiting segment must have close to a zero degree departure angle from the entering segment
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*Finally, grab the node and adjust such that the angle between the outbound segments is at least 15°:
# The other exiting segment must be of the type Ramp
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**If following the true natural departure angles of the outbound segments leads to an inner angle of more than 15°, then do so.
# The Ramp exiting segment must have a departure angle of between 20 and 30 degrees from the entering segment
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**If the outbound segments are equally straight ahead, ensure that the outbound paths at the node are '''essentially symmetrical'''.
 +
{{clear}}
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====Re-entry====
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Where a ramp or AGC enters the flow of traffic, the driver's path should do so smoothly and naturally. Place the final geometry handle at the gore point or end of the solid white line, then grab the node and pull it along the road to create a smooth, natural entry angle.
 +
[[File:EntranceRamp.jpg|900px]]
  
When those conditions are met, the navigation will present an "Exit Right/Left" instruction when the ramp is to be used, and will remain silent when the exiting  Highway/Freeway segment is to be used.
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Where an exit ramp ends at an intersection with a road, generally, map as you would any other intersection.
  
==== Exit naming ====
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*If an exit ramp forks into distinct and separate paths, particularly on either side of a painted or physical island, create a fork with multiple outbound ramp segments.
The Highway/Freeway segments before and after the junction should be named the same. The ramp segments should be named in accordance with the best practices in your location.
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*Where the ramp continues as a single roadway, and in some cases where a traffic island exists but is not particularly large or significant, a single ramp segment will suffice.
  
[[Road names/USA#Exit_ramps_and_Entrance_ramps_.28on-ramps.29|US Specific Ramp Names]]
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Generally, the same rules used to determine whether to map [[at-grade connectors]] can be used to determine whether to map a ramp island separately.
 +
<gallery>
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File:RampIslands.jpg|With a ramp island of significant size, use separate segments.
 +
File:Junction style simple ramp (2).PNG|Map as you would any normal intersection.
 +
</gallery>
 +
=={{anchor|Interchange types}}Mapping considerations==
 +
Consider the following when editing interchanges and their component junctions.
  
[[How_to_label_and_name_roads_%28United_Kingdom%29#Ramps_.28to.2Ffrom_Motorways_and_Dual_Carriageways.29|UK Specific Ramp Names]]
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===Turn instructions===
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Where the inbound segment is a {{Freeway}}, {{Major Highway}}, or {{Minor Highway}}, if an instruction is given to a specific outbound segment,
  
[[Road types and names|Naming standards for other areas]]
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*The default instruction to an outbound {{Ramp}} segment on the ''right'' will be "Exit right".
 +
*The default instruction to an outbound {{Ramp}} segment on the ''left'' will be "Keep left."
 +
*The default instruction to an outbound {{Freeway}}, {{Major Highway}}, or {{Minor Highway}} segment will be ''Keep left'' or ''Keep right''.
  
Editors covering areas that do not have specific best practices should review the existing guides for other areas, and determine which best matches the roadways of your area.
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As such, if a different instruction than the default is desired in any of these situations, use a [[turn instruction override]].
  
=== Freeway/highway splits ===
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===Road names===
A Highway/Freeway Split is when a Highway/Freeway segment meets at a junction with two other Highway/Freeway segments and there is no obvious straight through direction to a driver.
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Guidance for naming highway and ramp segments is found in the [[road names]] article.
  
==== Freeway split geometry ====
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====Concurrent routes====
: [[Image:Jct_fwy_fwy_split.png]]
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If an exit carries a concurrent route away from the highway (e.g., a U.S. highway that was carried by an interstate up to the exit but splits off at the exit), that route designation should be added as an alternate name on all ramp segments that carry it. Note that this may affect the expected behavior of [[audible instructions]], such that [[turn instruction override]]s may be needed.
  
To receive a navigation instruction for '''both''' branches of a split, the following must be true:
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====Using road name inheritance====
# All segments must be one of the three Highway/Freeway Types
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[[File:RampforkMUTCD.png|thumb]]
# All segments must have names which are different from each other
 
# The two exiting segments must have departure angles of 20 to 30 degrees from the entering segment
 
  
With those conditions met, the junction will present "Keep Left" and "Keep Right" navigation instructions using the name of the appropriate exiting segment.
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In some situations, name inheritance should be used to provide optimal instructions. If a ramp is unnamed ("no name" box checked), the name of the next named road along the route will propagate backwards in navigation instructions. This is useful both for the sake of simplicity and for giving more specific instructions to traffic at exits with ramp forks. If an unnamed ramp is used at an exit and subsequent named ramps are used after the fork, drivers will see the name of whichever side of the fork they need to go to before they exit the highway. This method will provide more sufficient notification of an approaching decision point than a named exit ramp would, and it should be used as long as the names of both ramp forks are visible on signs at the start of the initial ramp. If an exit ramp has multiple lanes with a sign or part of a sign over each lane, using this method can even function as a form of lane guidance. If the example on the right from the MUTCD were mapped using name inheritance, the ramp exiting I-42 would not be named. The ramp that goes to I-17 southbound would be named "Exit 36: I-17 S / Portland" and the ramp that goes to I-17 northbound would be named "Exit 36: I-17 N / Miami." This would produce the following instructions:
  
==== Freeway split naming ====
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*Traffic heading south on I-17 would receive
 +
*#at the exit: exit right to Exit 36: I-17 S / Portland
 +
*#at the fork: keep right to Exit 36: I-17 S / Portland
 +
*Traffic heading north on I-17 would receive
 +
*#at the exit: exit right to Exit 36: I-17 N / Miami
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*#at the fork: keep left to Exit 36: I-17 N / Miami
  
The primary rule is that all 3 segments at the junction must have different names.  That can be accomplished in one of two ways:
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Note that even though the exit number is by design not shown on signs at the ramp fork, it should be included in the names of the ramps for proper instructions at the exit. If signs at the ramp fork differ more significantly from signs at the exit, a different method of naming should be used.
# Using road names alone - It is an easy situation if all three roads which connect have different names.  If "Highway A" splits into "Highway B" and "Highway C", then that is all we need to have a properly functioning split.
 
# Using signs and [[#Wayfinder_Segments|Wayfinder Segments]] - If one of the branches of the split has the same name as the entering segment, we must create uniqueness at the junction. If "Highway X" splits off from "Highway Y" and "Highway X" continues as the other branch, the preferred approach is to use named [[#Wayfinder_Segments|Wayfinder Segments]].
 
  
=== Wayfinders ===
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=====Name inheritance, but signage on consecutive signs are different=====
 +
[[File:PseudoWF.png|thumb]]
  
It may be necessary to provide additional information to a driver for complex or confusing [[#Highway.2FFreeway_Exits|Exits]] and [[#Highway.2FFreeway_Splits|Splits]].  Examples of such situations include:
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If separate or split signs exist for traffic at an exit, but the signs at the ramp fork differ significantly from them, such as being further split or showing additional route numbers or control cities, the following method can be used:
* '''Lane Drops''' - Highway has been 3 lanes for miles and miles but only 2 lanes continue straight through at a certain point
 
* '''Inconsistent signage''' - Highway continues as a numbered route, but signs only call it by a name instead
 
* '''Non-obvious continuations''' - in a right hand drive country, exiting traffic is to the left and continuing traffic is to the right
 
  
In these cases we need to use short way-finder or path-finder segments which are named with the information displayed on the roadway signs.  There are two methods to accomplish this: using Highway/Freeways or using Ramps.
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#Leave the exit ramp unnamed
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#At the ramp fork create a turn instruction override for no instruction going into a stub ramp segment of {{:Segment length/Minimum}}
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#Name the stub according to the sign at the ''exit''
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#At the junction of the stub with the next ramp segment create a turn instruction override to match the expected instruction at the ramp fork, either keep left or right
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#Name the next ramp segment according to the sign at the ''ramp fork'' or leave it unnamed to inherit farther ramp names
  
* '''Highway/Freeways'''
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Because of name inheritance, the shortness of the stub, and the combination of turn instruction overrides, the name of the stub will be used in instructions at the exit, and the name of the ramp past the stub will be used at the ramp fork. This method should only be used when it's not possible to replicate what drivers see on guide signs using simple naming or name inheritance.
** Pro: provide a consistently rendered line on the map with no breaks
 
** Pro: does not introduce a [[Routing_penalties|routing penalty]] for the transition to Ramp type (although we do not know how much of an impact, if any, this has in actuality)
 
** Con: the long name of the segment may be displayed on the map creating clutter
 
** Con: the segment may be hard to see in the editor since it may blend in with the main Freeway
 
** Note: will provide "Keep Left" and "Keep Right" instructions
 
  
* '''Ramps'''
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===Wayfinders===
** Pro: ensures any long names are hidden from display on the map
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A '''[[wayfinder]]''' is defined as any junction configured to instruct drivers to stay on the road they're already on. Wayfinders are generally used where, for one reason or another, the continuation of the highway is not obvious to drivers. For criteria and further details on mapping wayfinders, see [[wayfinder]] and [[turn instruction override]].
** Pro: forces the client to stay zoomed in for the length of the segment to give a close view of the split to the driver
 
** Con: introduces a [[Routing_penalties|routing penalty]] of the transition to Ramp type (although we do not know how much of an impact, if any, this has in actuality)
 
** Con: may render as a broken line on the map
 
** Note: will provide "Keep Left" and "Exit Right" instructions in right-hand drive countries and "Exit Left" and "Keep Right" instructions in left-hand drive countries.
 
  
In both cases, the two exiting segments '''MUST''' have identical road types and different names from themselves and the entering segment.
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=={{Anchor|Interchange configurations}}Configurations==
  
Here we show Highway Y splitting off from Highway X.  By labeling segments with the information available on the road signs at the split, we have achieved uniqueness and provided additional useful information (the destination cities) to the driver.  We can achieve the desired results using either approach.  First as all Freeway segments:
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==={{anchor|Diamond interchange}}Diamond===
  
[[Image:Jct_fwy_fwy_wayfinder_fwy.png]]
+
:[[File:Diamond interchange.PNG|750px]]
  
And then using Ramps (which are named how they appear in the all Freeway example):
+
''See also: [[Wikipedia:Diamond_interchange|Diamond interchange article on Wikipedia]]''
  
[[Image:Jct_fwy_fwy_wayfinder_rmp.png]]
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Common in wide open spaces where land acquisition and geography are not concerns, this interchange design has ramps equally distributed across all 4 quadrants.
  
At times it is also necessary to use a way-finder at an Exit if a driver needs advance notice that only some lanes of the roadway continue straight through.  Again we can accomplish this using either of the two methods. First using Freeway segments for the split (the right branch wayfinder is un-named and the ramp segment that follows contains the appropriate name):
+
In the simplest form, this can be represented as single connections from the ramps to the surface street.  
  
[[Image:Jct_fwy_rmp_wayfinder_fwy.png]]
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The straight through motion from the exit ramp to the entrance ramp should typically be enabled, if legal to drive. Under normal circumstances, the big detour prevention mechanism discourages the routing server from routing someone off the freeway and directly back on. When the freeway path between the ramps is closed, or slow enough to overcome the Detour penalty, this off-on route may be given as a desirable alternative.
  
And then using Ramps (again, named the same as above):
+
Be aware that the big detour prevention penalty is intended to discourage routing that leaves a freeway (or highway) and returns to the same freeway (or highway). Therefore, at least one name (primary or alternate) of the freeway/highway segment before the exit ramp must exactly match one name (primary or alternate) of the freeway/highway segment after the entrance ramp to trigger the penalty. For further information see the [[Detour Prevention Mechanisms|big detour prevention mechanism]] page.
  
[[Image:Jct_fwy_rmp_wayfinder_rmp.png]]
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:[[Image:Jct_diamond_simple_turns_new.png]]
 +
 
 +
If the ramps connect to the surface street at multiple points, restrict turns which should use another ramp. Review the section on [[Junction Style Guide/Interchange#Ramp geometry and complexity|ramp geometry and complexity]] for more details on this topic.
 +
 
 +
First we see the turns that must be restricted for the exit ramps:
  
A rule of thumb for the way-finder segments is to make them 15 to 20 meters longThis keeps the segment small so we are less likely to see it in the client, but keeps it long enough to find and manipulate in the map editor. (In the near future, Way-finder segments may need to be greater than 5 meters long to prevent routing issues.)
+
:[[Image:Jct_diamond_cplx_turns_off_L_new.png]] [[Image:Jct_diamond_cplx_turns_off_R.png]]
  
=== Ramp-ramp splits ===
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Then we see what must be restricted for the entrance ramps:
A ramp may itself split and branch into two directions.  If this is the case, "Exit Right" and "Exit Left" will be announced using the name of the appropriate exiting segment in all cases.
 
  
==== Ramp split geometry ====
+
:[[Image:Jct_diamond_cplx_turns_on.png]]
: [[Image:Jct_ramp_ramp_split.png]]
 
  
==== Ramp split naming ====
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'''Note on elevation:'''
If ramps are unnamed, the name of a subsequent ramp will propagate backwards.  In the example above, if the two ramps exiting the junction are named, the ramp entering the junction can be left unnamed.  Then any navigation instruction directing you onto the first ramp would use the name of the appropriate exiting ramp.
+
The single surface street segment between the inner most ramps should be either raised or lowered in relation to the freeway segments depending on the actual geography at the interchange.
  
'''Example:''' The two ramps exiting the junction are named "DestinationLeft" and "DestinationRight".  The ramp that enters the junction is unnamed.  If you need to "Exit Right" onto the unnamed ramp.  If you are headed to "DestinationLeft", navigation would tell you:
+
==={{anchor|Cloverleaf interchange}}Cloverleaf===
* Exit Right to Destination Left
 
* Exit Left to Destination Left
 
  
Using unnamed ramps is very useful to provide sufficient notification of an approaching decision point, as long as the names of both ramp splits are visible on signs at the start of the initial ramp.
+
:[[Image:Jct_cloverleaf.png]]
  
'''Example of good use of unnamed ramps:'''
+
''See also: [[wikipedia:Cloverleaf_interchange|Cloverleaf Interchange article on Wikipedia]]''
* Initial Exit Sign: to City A and City B
 
* Destination Left Sign: to City A
 
* Destination Right Sign: to City B
 
Result: An unnamed initial ramp will provide accurate and informative navigation instructions to the driver.
 
  
'''Example of poor use of unnamed ramps:'''
+
In a cloverleaf Interchange, left turns are eliminated from all movements between the freeway and the surface street. First check the exit ramps.
* Initial Exit Sign: to Downtown
 
* Destination Left Sign: to Downtown
 
* Destination Right Sign: to Center St
 
Result: An unnamed ramp may create confusion since both Destination ramp names are NOT listed on the initial exit sign. In this case the initial ramp should be named.
 
  
'''Example of modified use of unnamed ramps:'''
+
:[[Image:Jct_cloverleaf_off_outer_turns.png]] [[Image:Jct_cloverleaf_off_inner_turns.png]]
  
* Initial Exit Sign: Exit 70A-B to City A and City B
+
Then check the entrance ramps for illegal turns.
* Destination Left Sign: to City A
 
* Destination Right Sign: to City B
 
* Destination Left name in Waze: Exit 70A: City A
 
* Destination Right name in Waze: Exit 70B: City B
 
Result: By using a modified name for the destination ramps, we have combined information from two sets of signs to generate the advance notice a driver may need to prepare for a decision point.
 
  
== Interchange configurations ==
+
:[[Image:Jct_cloverleaf_on_turns.png]]
Please see the [[Limited_Access_Interchange_Style_Guide|Limited Access Interchange Style Guide]].
 
  
=== Diamond interchange ===
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The connections to the freeway segments may be treated in two ways:
: [[Image:Jct_diamond.png]]
 
''See also: [http://en.wikipedia.org/wiki/Diamond_interchange Diamond Interchange article on Wikipedia]''
 
  
Common in wide open spaces where land acquisition and geography are not concerns, this Interchange design has ramps equally distributed across all 4 quadrants.
+
:[[Image:Jct_cloverleaf_options.png]]
  
In the simplest form, this can be represented as single connections from the ramps to the surface street.  
+
#(top) we can have the inner entrance and exit ramps have their own junction nodes with the freeway. Do '''not''' use this approach if there are [[#Collector.2FDistributor_Lanes|collector/distributor lanes]] (or a similar situation) involved.
 +
#(bottom) we can have the entrance and exit ramps share a single junction node with the freeway. This allows us to eliminate the very short freeway segment that may exist between the inner entrance and exit ramps.<br />It is best to offset this shared junction onto the entrance ramp side of the surface street. This prevents the junction from accidentally being connected to the surface street or looking like it does. We favor the entrance ramp side, because this would result in a slightly earlier exit instruction which is, of course, preferred over a late exit instruction. Use turn instruction overrides from the entrance ramp to give no instruction to the freeway and an exit instruction to the exit.
  
Note: Be sure to restrict the straight through motion from the exit ramp onto the entrance ramp on the other side of the road. This will prevent the routing server from trying to route someone off the freeway just to get back on it. Even though it may be a legal direction for a vehicle, turn restrictions are only for controlling routing directions.
+
The determining factor of which design to use will partly depend on the actual size and scale of the specific interchange and if there is a [[#Collector.2FDistributor_Lanes|collector/distributor]] involved.
  
: [[Image:Jct_diamond_simple_turns.png]]
+
'''Note on elevation: '''The single surface street segment between the inner most ramps should be either raised or lowered in relation to the freeway segments depending on the actual geography at the interchange.
  
If the ramps connect to the surface street at multiple points, ramp-to-ramp routing should be avoided as well as illegal turns which should use another ramp. Review the section [[Junction_Style_Guide#How_complex_should_ramps_be?|How complex should ramps be?]] in the Junction Style Guide for more details on this topic.
+
==={{anchor|Folded diamond interchange}}Folded diamond===
  
First we see the turns that must be restricted for the exit ramps:
+
:[[Image:Jct_folded_diamond.png]]
  
: [[Image:Jct_diamond_cplx_turns_off_L.png]]  [[Image:Jct_diamond_cplx_turns_off_R.png]]
+
''See also: Discussion of Folded Diamonds and A2/B2 Partial Cloverleafs on the [[wikipedia:Partial_cloverleaf_interchange|Partial Cloverleaf Interchange article on Wikipedia]]''
  
Then we see what must be restricted for the entrance ramps:
+
Geography or property ownership may prevent the ability for an interchange to be constructed with all ramps evenly distributed across the 4 quadrants of the interchange. When only two quadrants are used, it is typically called a folded diamond (basically a sub-type of a partial cloverleaf interchange). The ramps may be all on one side (as in the examples in this section) or they may be located in diagonally opposed quadrants.
  
: [[Image:Jct_diamond_cplx_turns_on.png]]
+
The unique situation presented by the folded diamond arrangement is having both entrance and exit ramps terminating on the same side of the surface street. Ideally both ramps should terminate on the same junction node to permit easy restriction of the illegal and usually impossible ramp-to-ramp movement.
  
'''Note on elevations:'''
+
:[[Image:Jct_folded_diamond_u-turn.png]]'
The single surface street segment between the inner most ramps should be either raised or lowered in relation to the freeway segments depending on the actual geography at the interchange.
 
  
=== Cloverleaf interchange ===
+
Like with a basic diamond interchange, often it will be necessary to represent the ramps making multiple connections to the surface street. Be sure to read the [[Junction_Style_Guide#Simple_is_better|Simple is better]] section in the Junction Style Guide.
: [[Image:Jct_cloverleaf.png]]
 
  
''See also: [http://en.wikipedia.org/wiki/Cloverleaf_interchange Cloverleaf Interchange article on Wikipedia]''
+
Restrict all non-permitted turns.
  
In a Cloverleaf Interchange, left turns are eliminated from all movements between the Freeway and the surface street. First check the exit ramps.
+
:[[Image:Jct_folded_diamond_off_turns_L.png]] [[Image:Jct_folded_diamond_off_turns_R.png]] [[Image:Jct_folded_diamond_on_turns.png]]
  
: [[Image:Jct_cloverleaf_off_outer_turns.png]] [[Image:Jct_cloverleaf_off_inner_turns.png]]
+
'''Note on elevation:''' Similar to a basic diamond interchange, in most cases only the segment of the surface street that crosses the Freeway segments will need to be adjusted up or down.
  
Then check the entrance ramps for illegal turns.
+
===Single-point urban interchange (SPUI)===
  
: [[Image:Jct_cloverleaf_on_turns.png]]
+
:[[File:SPUI.PNG|750px]]
  
The connections to the Freeway segments may be treated in two ways:
+
''See also: [[wikipedia:Single-point_urban_interchange|Single Point Urban Interchange article on Wikipedia]]''
  
:[[Image:Jct_cloverleaf_options.png]]
+
A SPUI is a very space and flow efficient design, but it takes extra attention to ensure the turns are correct. And as the name indicates, ideally there should be a single junction in the center. You may need to tweak the geometry of segments a bit off of alignment from the real physical world, but it should be minor if the interchange is a true SPUI.
  
# (top) we can have the inner entrance and exit ramps have their own junction nodes with the Freeway. Do '''NOT''' use this approach if there are [[#Collector.2FDistributor_Lanes|Collector/Distributor Lanes]] (or a similar situation) involved.
+
The outer branches of the exit ramps are similar to a diamond interchange and ramp to ramp routing should be enabled if possible and legal. However, in many SPUIs such ramp to ramp routing is not possible:
# (bottom) we can have the entrance and exit ramps share a single junction node with the Freeway. This allows us to eliminate the very short Freeway segment that may exist between the inner entrance and exit ramps.<br />It is best to offset this shared junction onto the Entrance ramp side of the surface street. This prevents the junction from accidentally being connected to the surface street or looking like it does. We favor the Entrance ramp side, because this would result in a slightly earlier exit instruction which is of course preferred over a late exit instruction.
 
  
The determining factor of which design to use will partly depend on the actual size and scale of the specific interchange and if there is a [[#Collector.2FDistributor_Lanes|Collector/Distributor]] involved.
+
:[[File:SPUI outer branch.PNG|500px]]
  
'''Note on Elevation:'''
+
Where things get complicated is the inner branches leading to the single point.  You need to avoid ramp-to-ramp in two directions and a reverse flow turn. '''Note:''' The ramp-to-ramp motion to facilitate a U-turn (the top left arrow in the image below) may or may not be allowed depending on the specific interchange.  Please validate this turn.
The single surface street segment between the inner most ramps should be either raised or lowered in relation to the freeway segments depending on the actual geography at the interchange.
 
  
=== Folded diamond interchange ===
+
:[[File:SPUI inner branch.PNG|700px]]
: [[Image:Jct_folded_diamond.png]]
 
''See also: Discussion of Folded Diamonds and A2/B2 Partial Cloverleafs on the [http://en.wikipedia.org/wiki/Partial_cloverleaf_interchange Partial Cloverleaf Interchange article on Wikipedia]''
 
  
Geography or property ownership may prevent the ability for an interchange to be constructed with all ramps evenly distributed across the 4 quadrants of the interchange. When only two quadrants are used, it is typically called a Folded Diamond (basically a sub-type of a Partial Cloverleaf Interchange). The ramps may be all on one side (as in the examples in this section) or they may be located in diagonally opposed quadrants.
+
Luckily the entrance ramp restrictions are similar to the diamond interchange:
  
The unique situation presented by the Folded Diamond arrangement is having both Entrance and Exit ramps terminating on the same side of the surface street. Ideally both ramps should terminate on the same junction node to permit us to easily restrict the illegal and usually impossible ramp-to-ramp movement.
+
:[[File:SPUI middle branch.PNG|400px]]
  
: [[Image:Jct_folded_diamond_u-turn.png]]'
+
If you were to look at all the restricted turns at once, you may get the false impression that something is very wrong. But as you now know, a SPUI has almost as many restricted turns as allowed ones.
  
Like with a basic Diamond Interchange, often it will be necessary to represent the ramps making multiple connections to the surface street. Be sure to read the article [[Junction_Style_Guide#How_complex_should_ramps_be?|How complex should ramps be?]] in the Junction Style Guide.
+
:[[File:SPUI disabled turns.PNG|300px]]
  
Restrict all non-permitted turns.
+
'''Note on Elevation: '''The two surface street segments (between the outer ramps and connected to the single point) and the four ramp segments connected to the single point should all be the same level, either one higher or one lower than the elevation of the freeway segments above/below the single point.
  
: [[Image:Jct_folded_diamond_off_turns_L.png]] [[Image:Jct_folded_diamond_off_turns_R.png]] [[Image:Jct_folded_diamond_on_turns.png]]
+
==={{Anchor|Collector/Distributor Lanes}}Collector/distributor lanes===
  
'''Note on Elevation:''' Similar to a basic Diamond interchange, in most cases only the segment of the surface street that crosses the Freeway segments will need to be adjusted up or down.
+
These are lanes parallel to, but physically separated from, the lanes of a Freeway that serve to keep merging traffic out of the flow of through traffic on the mainline freeway.
  
=== Single-point urban interchange (SPUI) ===
+
Collector/distributor lanes serve as either:
: [[Image:Jct_SPUI.png]]
 
''See also: [http://en.wikipedia.org/wiki/Single-point_urban_interchange Single Point Urban Interchange article on Wikipedia]''
 
  
A SPUI is a very space and flow efficient design, but it takes extra attention to ensure the turns are correct. And as the name indicates, ideally there should be a single junction in the center. You may need to tweak the geometry of segments a bit off of alignment from the real physical world, but it should be minor if the interchange is a true SPUI.
+
*some of the ramps in an '''interchange''', or
 +
*local lanes in configurations with '''[[wikipedia:local-express lanes|local-express lanes]]'''.
  
The outer branches of the exit ramps are very much like in the case of a diamond interchange:
 
  
: [[Image:Jct_SPUI_off_outer_turn.png]]
+
===={{anchor|Collector/distributor interchanges}}Collector/distributor interchange====
  
Where things get complicated is the inner branches leading to the Single Point.  You need to avoid ramp-to-ramp in two directions and a reverse flow turn. '''Note:''' The ramp-to-ramp motion to facilitate a U-Turn (the top left arrow in the image below) may or may not be allowed depending on the specific interchange.  Please validate this turn.
+
Some interchange configurations make use of collector/distributor lanes to separate lower-speed merging traffic from high-speed through traffic. This is often used in cloverleaf interchanges and in groups of nearby exits.
  
: [[Image:Jct_SPUI_off_inner_turn.png]]
+
=====Collector/distributor cloverleaf=====
  
Luckily the entrance ramp restrictions are similar to the diamond interchange:
+
This is a cloverleaf interchange that is connected to a collector/distributor instead of directly to the main roadway. Map collector-distributor cloverleaf ramps as you would any other ramp.
  
: [[Image:Jct_SPUI_on_turn.png]]
+
[[Image:Jct_fc_cloverleaf_bad.png]]
  
If you were to look at all the restricted turns at once, you may get the false impression that something is very wrong. But as you now know, a SPUI has almost as many restricted turns as allowed ones.
+
The [[Detour Prevention Mechanisms|detour prevention mechanism]] will discourage Waze from routing users onto the collector-distributor and back onto the freeway – as long as the street name on the freeway is the same before, throughout, and after the collector-distributor. Previously this feature was not available and the ramps were set up to restrict the through route. Some of these ramp configurations may still be set up that way, so they can now be configured as pictured above with the through route enabled.
  
: [[Image:Jct_SPUI_all_turns.png]]
+
===={{anchor|Complex collector/distributor interchanges}}Complex collector/distributor interchange====
  
'''Note on Elevation:'''
+
[[Image:Collector-distributor-exit.png|thumb|right|450px|Collector-distributor lanes used in an interchange on I-81 in Christiansburg, Virginia (Exits 118A-B-C)]]
The two surface street segments (between the outer ramps and connected to the Single Point) and the 4 ramp segments connected to the single point should all be the same level, either one higher or one lower than the elevation of the freeway segments above/below the single point.
 
  
=== Collector/distributor interchanges ===
+
Where collector/distributor lanes are used as part of an interchange, use the {{Ramp}} type for the collector/distributor lanes. Name the ramp segments as you would any other ramp segment.
  
These are lanes parallel to but physically separated from the lanes of a Limited Access Road that serve to keep merging traffic out of the flow of through traffic on the mainline Freeway.
+
Ensure that a name on the Freeway segments is consistent before and after the collector/distributor lanes, so that the [[Detour Prevention Mechanisms|detour prevention mechanism]] will prevent Waze from routing users erroneously.
  
==== Collector/distributor cloverleaf ====
+
{{clear}}
  
This is a Cloverleaf interchange that is connected to a Collector/Distributor instead of directly to the main roadway. Here is an example which matches the physical world but has a major deficiency.
+
====Local-express lanes====
  
[[Image:Jct_fc_cloverleaf_bad.png]]
+
[[Image:Local-express.png|thumb|right|450px|A local-express lane configuration on I-96 in Livonia, Michigan]]
  
At first it appears that this layout allows everyone to get where they are going.  The problem is that it allows MORE than it should. It is possible to exit the mainline Freeway and stay on the Collector/Distributor, bypassing the Cloverleaf, and merge back onto the mainline Freeway.
+
Local-express lanes are similar to collector/distributor interchange, but on a larger scale. While collector/distributor interchanges typically have an exit number or numbers, local-express lanes typically share the same name, differentiated by "Local" for the collector/distributor lanes and "Express" for the thru lanes.
  
Although this may be a way to avoid traffic on the mainline Freeway, doing so is inefficient, may be unsafe, and is outright illegal in some areas. Therefore we need to tweak our design a little...
+
A local-express lane configuration is not technically an "interchange"; however, since its physical characteristics are similar to those of a complex collector/distributor interchange, it is discussed here.
  
[[Image:Jct_fc_cloverleaf_good.png]]
+
Where collector/distributor lanes are used as part of a local-express lane configuration,
  
In this example, we have eliminated the ramp segment joining the two loops of the cloverleaf and the Collector/Distributor ramps. Now they all connect at a single point and we are therefore able to restrict the turn that allowed drivers to use the Collector/Distributor as a bypass.
+
*use the same type (most likely {{Freeway}}) for the local lanes as is used for the express lanes, and
 +
*name the road as it is signed: typically "[Name] Local [Direction]": for example, "I-96 Local W" for local lanes (and "I-96 Express W" for the corresponding express lanes).
  
==== Complex collector/distributor ====
+
{{clear}}
  
A Collector/Distributor is considered complex if there are multiple exits and entrances connected to the Collector/Distributor.
+
==={{Anchor|
 +
Diverging diamond interchange (DDI)|Diverging diamond interchange|Diverging_diamond_interchange|DDI}}Diverging diamond (DDI)===
  
Ideally you will '''not''' have to implement any of the complex layouts described in this section.  Start by representing the ramps in the simplest manner possible and see how they perform for a while. If everything is mapped correctly and navigation still tries to have drivers bypass the mainline Freeway, then and only then modify the layout with the following suggestions.
+
''See also:'' [[Wikipedia:Diverging_diamond_interchange|Diverging Diamond Interchange]] article on Wikipedia.
 +
[[File:DDI Example Dupont.png|thumb|845x845px|none]]
 +
Diverging diamond interchanges (DDI) are a type of diamond interchange in which the two directions of traffic cross one another on each side of a limited-access roadway. A DDI may pass over or under the limited-access roadway.
  
If we are lucky, we can still restrict the bypass movement with the single central node like we did for the [[#Collector.2FDistributor_Cloverleaf|Collector/Distributor Cloverleaf]] example.  Notice how all the exits are either before or at the central node (highlighted in the next image) and all the entrances are at or after the central node.
+
This type of interchange is unusual, in that it requires traffic to briefly drive on the opposite side of the road from what is customary for the jurisdiction. However, the design of the Diverging Diamond Interchange controls the driver's line of sight to ensure the cross-over action feels natural and goes unnoticed.
  
[[Image:Jct_cmplx_collector_1.png]]
+
====Segment directionality====
 +
[[File:DDI Example Dupont - traffic flow.png|thumb|848x848px|Flow of traffic within a diverging diamond interchange|none]]
 +
All ramp and surface street segments are set as one-way. If you are creating a DDI along a road which is not divided, divide the road, first. {{Details|Best map_editing_practice#Dividing_and_un-dividing_divided_highways{{!}}Best map editing practice § Dividing and un-dividing divided highways|how to properly divide/un-divide a road}}
  
It becomes more complicated if entrances and exits are more mixed. In the following example, there is an entrance before an exit and the highlighted path shows this entering traffic crossing the exiting traffic we dealt with in previous examples. If we use the same restricted turn on the same node as in previous examples, we block traffic entering from the right-most entrance from being able to get to the mainline Freeway. If we enable that turn, now we are no longer blocking the bypass movement.
+
====At-grade intersections====
  
[[Image:Jct_cmplx_collector_2a.png]]
+
=====Junctions=====
  
To get the control we require, we need to run the entrance ramp up to the node of the last exit. This allows the exiting traffic to be kept separate from the entering traffic. In the next example, we have modified the right-most entrance so it connects further down the Collector/Distributor. Even if the Collector/Distributor itself is only one lane, we want to have these parallel road segments through the area. They can be close together, but do not overlap them. You will have segments overlapping, but be sure not to junction them together.
+
As with all at-grade intersections in Waze, all DDI at-grade intersections are modeled with junction nodes, ''including'' the two signaled intersections where opposing directions of traffic "cross over" each other (inner surface road junctions). A DDI may also have two outer surface road junctions, where the one-way segments transition to two-way road segments.
  
[[Image:Jct_cmplx_collector_2b.png]]
+
=====Turn restrictions=====
  
Now we can restrict the exiting traffic from using the Collector/Distributor as a bypass of the mainline Freeway as we have previously without impacting the entering traffic.
+
======Overview======
 +
There are four junctions in a DDI at which the turn restrictions must be checked - two inner surface road junctions where traffic crosses, and two outer surface road junctions where the road divides/joins on each side of the DDI.[[File:DDI Example Dupont - turn restrictions.png|thumb|871x871px|All restricted turns within a DDI (displayed by using Shift+Z).|none]]
  
In a more complicated case, you will need to create parallel paths for exiting and entering traffic for a majority of the Collector/Distributor's length. In the following example, the path for exiting traffic is highlighted and the ramps available for entering traffic appear normally. There is no mixing of entering and exiting traffic in this logical view of the Collector/Distributor even if traffic is mixing in reality.
+
======Inner surface road junctions======
 +
[[File:DDI Example Dupont - turn restrictions - inner - 01.png|none|thumb|871x871px]]
 +
[[File:DDI Example Dupont - turn restrictions - outer - 02.png|none|thumb|870x870px]]Disable the ''two'' turns from one-way segments to the segments carrying traffic the ''opposite'' direction at both inner surface road intersections, for a total of four disabled turns.  
  
[[Image:Jct_cmplx_collector_3.png]]
+
======Outer surface road junctions======
 +
[[File:DDI Example Dupont - turn restrictions - outer.png|none|thumb|871x871px]]
 +
Disable the ''single'' turn from the one-way segment carrying traffic ''exiting'' the DDI to the one-way segment carrying traffic ''entering'' the DDI at both outer surface road intersections, for a total of two disabled turns.
  
As a worse case scenario, you may have a situation where traffic can enter early in the Collector/Distributor and can legally exit at any of the exits along the Collector/Distributor. In this case you will need to carefully create junctions with restricted turns or even additional ramps to enable the legal movements.
+
==See also==
  
== See also ==
+
Review the [[Wikipedia:Interchange_(road)|Wikipedia article on road Interchanges]] for further information on this topic.
  
Review the [http://en.wikipedia.org/wiki/Interchange_(road) Wikipedia article on Road Interchanges] for further information on this topic.
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{{ReturnTo | Junction_Style_Guide | the Junction Style Guide}}
 +
[[Category:Style Guides]]

Latest revision as of 19:27, 26 November 2020

An interchange is a road junction where traffic can move between roads that do not intersect. The roads are connected by ramps, and if they cross, the crossing is grade-separated. They are most commonly used where one or more roads is a controlled-access highway. Complex interchanges may contain many highways and local roads meeting within small areas. Many different layouts have been developed by traffic engineers to optimize interchanges for size, complexity, traffic safety, navigation, and unimpeded traffic flow.

This article is a sub-article of the Junction Style Guide. As such, this article is a style guide as well. Representing interchanges on the map can be exacting and difficult. The guidance on this page will help editors to create accurate and usable map versions of these interchanges. The following sections discuss the proper style for ramps, interchanges, and some common interchange designs. Note that some interchanges may be a hybrid of these basic designs where one side or quadrant of the interchange may differ from the others. Also note that since interchanges often involve grade-separated crossings, the road elevation of the segments becomes important. If two roads cross without connecting directly, their elevations must be different.

Before reading through this article, be sure to fully understand the information in the Junction Style Guide.

Ramps

Ramps have a very specific purpose in Waze. They are intended to connect segments of minor highways, major highways, and freeways to roads where there are no at-grade crossings.

The  Ramp  type is used extensively in interchanges for three reasons.

  • Ramp segment names are not displayed on the map.
  • Ramp segments have essentially no penalty, so they can be used to connect freeways and major highways with each other without causing problems.
  • Ramp segments are relatively thin but show at wide zoom levels, so interchanges do not distract from highways but can be seen at high speeds.

When to use ramps

Use of the  Ramp  type is governed by the following rules:

Geometry

Exits, forks, and wayfinders

This section concerns the geometry of the following junctions:

  • exits, which are junctions at which one outbound segment (typically a ramp) carries traffic off of a road and the other outbound segment continues the same road as the entry segment;
  • forks, which are junctions at which either both or neither outbound segment continues the same road as the entry segment; and
  • wayfinders, a type of exit or fork which is set up to instruct the driver to stay on the road they're already on.

When mapping an exit or fork (or wayfinder), there is one guiding question: is there one clear straight-ahead path? That is, does one and only one outbound segment clearly continue the same path as the inbound segment?

Where there is a clear straight ahead path

The straight ahead path should be more or less straight, with a smooth transition.

The diverging path should be configured as follows:

  • First, place the first geometry handle of the diverging segment as follows:
    • on freeway exits and other similarly-configured ramps, at the nearest point to the exit from the following:
      • If there's no solid white line, at the gore point (or "theoretical gore", i.e., where the painted lines diverge)
      • If there's a solid white line, at its beginning
      • On a multi-lane exit, at the gore point or solid white line between the inner exit lane and the adjacent continuing lane
      • 1/4 mile before the gore point, on exits with a longer solid white line
      • Halfway between the gore points of the exit and the previous exit
    • on at-grade connectors, at the gore point.
      Use the natural departure angle for a segment with a true departure angle of at least 20°.
  • Next, grab the node itself, where the segments meet, and adjust the geometry of the exit itself as follows:
    • If the actual path of the exit diverges from the inbound path by less than 20°, adjust the node to create a 20° departure angle. This will allow for consistent timing of exit instructions and make it easier to report closures in the Waze client.
    • If the actual path of the exit diverges immediately from the inbound path by more than 20°, adjust the node such that the exit path follows its true natural departure angle.
  • Finally, ensure that the last geometry handle before the node is at least 40 feet ahead of the node, and that the second geometry handle on the diverging path is at least 40 feet beyond the first geometry handle.

ExitRampShort.jpg

Where there is not a clear straight ahead path

Essentially symmetrical: yes, departure angles of outbound segments are very close (7° and 8°). At least 15°: yes (de-select any segments and select the node to check).

Whether both outbound paths are or neither outbound path is straight ahead:

  • First, adjust the inbound segment geometry to follow the inbound segment's true path.
  • Next, set the first geometry handles of both outbound segments in line with the gore point.
  • Finally, grab the node and adjust such that the angle between the outbound segments is at least 15°:
    • If following the true natural departure angles of the outbound segments leads to an inner angle of more than 15°, then do so.
    • If the outbound segments are equally straight ahead, ensure that the outbound paths at the node are essentially symmetrical.

Re-entry

Where a ramp or AGC enters the flow of traffic, the driver's path should do so smoothly and naturally. Place the final geometry handle at the gore point or end of the solid white line, then grab the node and pull it along the road to create a smooth, natural entry angle. EntranceRamp.jpg

Where an exit ramp ends at an intersection with a road, generally, map as you would any other intersection.

  • If an exit ramp forks into distinct and separate paths, particularly on either side of a painted or physical island, create a fork with multiple outbound ramp segments.
  • Where the ramp continues as a single roadway, and in some cases where a traffic island exists but is not particularly large or significant, a single ramp segment will suffice.

Generally, the same rules used to determine whether to map at-grade connectors can be used to determine whether to map a ramp island separately.

Mapping considerations

Consider the following when editing interchanges and their component junctions.

Turn instructions

Where the inbound segment is a  Freeway ,  Major Highway , or  Minor Highway , if an instruction is given to a specific outbound segment,

  • The default instruction to an outbound  Ramp  segment on the right will be "Exit right".
  • The default instruction to an outbound  Ramp  segment on the left will be "Keep left."
  • The default instruction to an outbound  Freeway ,  Major Highway , or  Minor Highway  segment will be Keep left or Keep right.

As such, if a different instruction than the default is desired in any of these situations, use a turn instruction override.

Road names

Guidance for naming highway and ramp segments is found in the road names article.

Concurrent routes

If an exit carries a concurrent route away from the highway (e.g., a U.S. highway that was carried by an interstate up to the exit but splits off at the exit), that route designation should be added as an alternate name on all ramp segments that carry it. Note that this may affect the expected behavior of audible instructions, such that turn instruction overrides may be needed.

Using road name inheritance

RampforkMUTCD.png

In some situations, name inheritance should be used to provide optimal instructions. If a ramp is unnamed ("no name" box checked), the name of the next named road along the route will propagate backwards in navigation instructions. This is useful both for the sake of simplicity and for giving more specific instructions to traffic at exits with ramp forks. If an unnamed ramp is used at an exit and subsequent named ramps are used after the fork, drivers will see the name of whichever side of the fork they need to go to before they exit the highway. This method will provide more sufficient notification of an approaching decision point than a named exit ramp would, and it should be used as long as the names of both ramp forks are visible on signs at the start of the initial ramp. If an exit ramp has multiple lanes with a sign or part of a sign over each lane, using this method can even function as a form of lane guidance. If the example on the right from the MUTCD were mapped using name inheritance, the ramp exiting I-42 would not be named. The ramp that goes to I-17 southbound would be named "Exit 36: I-17 S / Portland" and the ramp that goes to I-17 northbound would be named "Exit 36: I-17 N / Miami." This would produce the following instructions:

  • Traffic heading south on I-17 would receive
    1. at the exit: exit right to Exit 36: I-17 S / Portland
    2. at the fork: keep right to Exit 36: I-17 S / Portland
  • Traffic heading north on I-17 would receive
    1. at the exit: exit right to Exit 36: I-17 N / Miami
    2. at the fork: keep left to Exit 36: I-17 N / Miami

Note that even though the exit number is by design not shown on signs at the ramp fork, it should be included in the names of the ramps for proper instructions at the exit. If signs at the ramp fork differ more significantly from signs at the exit, a different method of naming should be used.

Name inheritance, but signage on consecutive signs are different
PseudoWF.png

If separate or split signs exist for traffic at an exit, but the signs at the ramp fork differ significantly from them, such as being further split or showing additional route numbers or control cities, the following method can be used:

  1. Leave the exit ramp unnamed
  2. At the ramp fork create a turn instruction override for no instruction going into a stub ramp segment of 19.69 ft (6 m)
  3. Name the stub according to the sign at the exit
  4. At the junction of the stub with the next ramp segment create a turn instruction override to match the expected instruction at the ramp fork, either keep left or right
  5. Name the next ramp segment according to the sign at the ramp fork or leave it unnamed to inherit farther ramp names

Because of name inheritance, the shortness of the stub, and the combination of turn instruction overrides, the name of the stub will be used in instructions at the exit, and the name of the ramp past the stub will be used at the ramp fork. This method should only be used when it's not possible to replicate what drivers see on guide signs using simple naming or name inheritance.

Wayfinders

A wayfinder is defined as any junction configured to instruct drivers to stay on the road they're already on. Wayfinders are generally used where, for one reason or another, the continuation of the highway is not obvious to drivers. For criteria and further details on mapping wayfinders, see wayfinder and turn instruction override.

Configurations

Diamond

Diamond interchange.PNG

See also: Diamond interchange article on Wikipedia

Common in wide open spaces where land acquisition and geography are not concerns, this interchange design has ramps equally distributed across all 4 quadrants.

In the simplest form, this can be represented as single connections from the ramps to the surface street.

The straight through motion from the exit ramp to the entrance ramp should typically be enabled, if legal to drive. Under normal circumstances, the big detour prevention mechanism discourages the routing server from routing someone off the freeway and directly back on. When the freeway path between the ramps is closed, or slow enough to overcome the Detour penalty, this off-on route may be given as a desirable alternative.

Be aware that the big detour prevention penalty is intended to discourage routing that leaves a freeway (or highway) and returns to the same freeway (or highway). Therefore, at least one name (primary or alternate) of the freeway/highway segment before the exit ramp must exactly match one name (primary or alternate) of the freeway/highway segment after the entrance ramp to trigger the penalty. For further information see the big detour prevention mechanism page.

Jct diamond simple turns new.png

If the ramps connect to the surface street at multiple points, restrict turns which should use another ramp. Review the section on ramp geometry and complexity for more details on this topic.

First we see the turns that must be restricted for the exit ramps:

Jct diamond cplx turns off L new.png Jct diamond cplx turns off R.png

Then we see what must be restricted for the entrance ramps:

Jct diamond cplx turns on.png

Note on elevation: The single surface street segment between the inner most ramps should be either raised or lowered in relation to the freeway segments depending on the actual geography at the interchange.

Cloverleaf

Jct cloverleaf.png

See also: Cloverleaf Interchange article on Wikipedia

In a cloverleaf Interchange, left turns are eliminated from all movements between the freeway and the surface street. First check the exit ramps.

Jct cloverleaf off outer turns.png Jct cloverleaf off inner turns.png

Then check the entrance ramps for illegal turns.

Jct cloverleaf on turns.png

The connections to the freeway segments may be treated in two ways:

Jct cloverleaf options.png
  1. (top) we can have the inner entrance and exit ramps have their own junction nodes with the freeway. Do not use this approach if there are collector/distributor lanes (or a similar situation) involved.
  2. (bottom) we can have the entrance and exit ramps share a single junction node with the freeway. This allows us to eliminate the very short freeway segment that may exist between the inner entrance and exit ramps.
    It is best to offset this shared junction onto the entrance ramp side of the surface street. This prevents the junction from accidentally being connected to the surface street or looking like it does. We favor the entrance ramp side, because this would result in a slightly earlier exit instruction which is, of course, preferred over a late exit instruction. Use turn instruction overrides from the entrance ramp to give no instruction to the freeway and an exit instruction to the exit.

The determining factor of which design to use will partly depend on the actual size and scale of the specific interchange and if there is a collector/distributor involved.

Note on elevation: The single surface street segment between the inner most ramps should be either raised or lowered in relation to the freeway segments depending on the actual geography at the interchange.

Folded diamond

Jct folded diamond.png

See also: Discussion of Folded Diamonds and A2/B2 Partial Cloverleafs on the Partial Cloverleaf Interchange article on Wikipedia

Geography or property ownership may prevent the ability for an interchange to be constructed with all ramps evenly distributed across the 4 quadrants of the interchange. When only two quadrants are used, it is typically called a folded diamond (basically a sub-type of a partial cloverleaf interchange). The ramps may be all on one side (as in the examples in this section) or they may be located in diagonally opposed quadrants.

The unique situation presented by the folded diamond arrangement is having both entrance and exit ramps terminating on the same side of the surface street. Ideally both ramps should terminate on the same junction node to permit easy restriction of the illegal and usually impossible ramp-to-ramp movement.

Jct folded diamond u-turn.png'

Like with a basic diamond interchange, often it will be necessary to represent the ramps making multiple connections to the surface street. Be sure to read the Simple is better section in the Junction Style Guide.

Restrict all non-permitted turns.

Jct folded diamond off turns L.png Jct folded diamond off turns R.png Jct folded diamond on turns.png

Note on elevation: Similar to a basic diamond interchange, in most cases only the segment of the surface street that crosses the Freeway segments will need to be adjusted up or down.

Single-point urban interchange (SPUI)

SPUI.PNG

See also: Single Point Urban Interchange article on Wikipedia

A SPUI is a very space and flow efficient design, but it takes extra attention to ensure the turns are correct. And as the name indicates, ideally there should be a single junction in the center. You may need to tweak the geometry of segments a bit off of alignment from the real physical world, but it should be minor if the interchange is a true SPUI.

The outer branches of the exit ramps are similar to a diamond interchange and ramp to ramp routing should be enabled if possible and legal. However, in many SPUIs such ramp to ramp routing is not possible:

SPUI outer branch.PNG

Where things get complicated is the inner branches leading to the single point. You need to avoid ramp-to-ramp in two directions and a reverse flow turn. Note: The ramp-to-ramp motion to facilitate a U-turn (the top left arrow in the image below) may or may not be allowed depending on the specific interchange. Please validate this turn.

SPUI inner branch.PNG

Luckily the entrance ramp restrictions are similar to the diamond interchange:

SPUI middle branch.PNG

If you were to look at all the restricted turns at once, you may get the false impression that something is very wrong. But as you now know, a SPUI has almost as many restricted turns as allowed ones.

SPUI disabled turns.PNG

Note on Elevation: The two surface street segments (between the outer ramps and connected to the single point) and the four ramp segments connected to the single point should all be the same level, either one higher or one lower than the elevation of the freeway segments above/below the single point.

Collector/distributor lanes

These are lanes parallel to, but physically separated from, the lanes of a Freeway that serve to keep merging traffic out of the flow of through traffic on the mainline freeway.

Collector/distributor lanes serve as either:

  • some of the ramps in an interchange, or
  • local lanes in configurations with local-express lanes.


Collector/distributor interchange

Some interchange configurations make use of collector/distributor lanes to separate lower-speed merging traffic from high-speed through traffic. This is often used in cloverleaf interchanges and in groups of nearby exits.

Collector/distributor cloverleaf

This is a cloverleaf interchange that is connected to a collector/distributor instead of directly to the main roadway. Map collector-distributor cloverleaf ramps as you would any other ramp.

Jct fc cloverleaf bad.png

The detour prevention mechanism will discourage Waze from routing users onto the collector-distributor and back onto the freeway – as long as the street name on the freeway is the same before, throughout, and after the collector-distributor. Previously this feature was not available and the ramps were set up to restrict the through route. Some of these ramp configurations may still be set up that way, so they can now be configured as pictured above with the through route enabled.

Complex collector/distributor interchange

Collector-distributor lanes used in an interchange on I-81 in Christiansburg, Virginia (Exits 118A-B-C)

Where collector/distributor lanes are used as part of an interchange, use the  Ramp  type for the collector/distributor lanes. Name the ramp segments as you would any other ramp segment.

Ensure that a name on the Freeway segments is consistent before and after the collector/distributor lanes, so that the detour prevention mechanism will prevent Waze from routing users erroneously.

Local-express lanes

A local-express lane configuration on I-96 in Livonia, Michigan

Local-express lanes are similar to collector/distributor interchange, but on a larger scale. While collector/distributor interchanges typically have an exit number or numbers, local-express lanes typically share the same name, differentiated by "Local" for the collector/distributor lanes and "Express" for the thru lanes.

A local-express lane configuration is not technically an "interchange"; however, since its physical characteristics are similar to those of a complex collector/distributor interchange, it is discussed here.

Where collector/distributor lanes are used as part of a local-express lane configuration,

  • use the same type (most likely  Freeway ) for the local lanes as is used for the express lanes, and
  • name the road as it is signed: typically "[Name] Local [Direction]": for example, "I-96 Local W" for local lanes (and "I-96 Express W" for the corresponding express lanes).

Diverging diamond (DDI)

See also: Diverging Diamond Interchange article on Wikipedia.

DDI Example Dupont.png

Diverging diamond interchanges (DDI) are a type of diamond interchange in which the two directions of traffic cross one another on each side of a limited-access roadway. A DDI may pass over or under the limited-access roadway.

This type of interchange is unusual, in that it requires traffic to briefly drive on the opposite side of the road from what is customary for the jurisdiction. However, the design of the Diverging Diamond Interchange controls the driver's line of sight to ensure the cross-over action feels natural and goes unnoticed.

Segment directionality

Flow of traffic within a diverging diamond interchange

All ramp and surface street segments are set as one-way. If you are creating a DDI along a road which is not divided, divide the road, first.

For more details on how to properly divide/un-divide a road, see Best map editing practice § Dividing and un-dividing divided highways.

At-grade intersections

Junctions

As with all at-grade intersections in Waze, all DDI at-grade intersections are modeled with junction nodes, including the two signaled intersections where opposing directions of traffic "cross over" each other (inner surface road junctions). A DDI may also have two outer surface road junctions, where the one-way segments transition to two-way road segments.

Turn restrictions
Overview

There are four junctions in a DDI at which the turn restrictions must be checked - two inner surface road junctions where traffic crosses, and two outer surface road junctions where the road divides/joins on each side of the DDI.

All restricted turns within a DDI (displayed by using Shift+Z).
Inner surface road junctions
DDI Example Dupont - turn restrictions - inner - 01.png
DDI Example Dupont - turn restrictions - outer - 02.png

Disable the two turns from one-way segments to the segments carrying traffic the opposite direction at both inner surface road intersections, for a total of four disabled turns.

Outer surface road junctions
DDI Example Dupont - turn restrictions - outer.png

Disable the single turn from the one-way segment carrying traffic exiting the DDI to the one-way segment carrying traffic entering the DDI at both outer surface road intersections, for a total of two disabled turns.

See also

Review the Wikipedia article on road Interchanges for further information on this topic.