Difference between revisions of "Junction Style Guide/Interchange"

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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]].
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== Ramps ==
 
== 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
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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.
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* 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.
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* 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 ===
 
=== 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]]
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* [[Road types]]
 
* [[At-grade connectors]]
 
* [[At-grade connectors]]
  
 
=== Ramp geometry and complexity ===
 
=== Ramp geometry and complexity ===
  
When placing the beginning of a ramp, place the first [[geometry node]] of the ramp segment at the point where the solid white line begins, and extend the ramp naturally to create a junction with the road segment, typically at about a 10° angle. This will allow for consistent timing of exit instructions.
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[[File:exitcomparison.png|thumb|Divergence is 12.5° on the left and 22.5° on the right. No angle between outgoing segments should ever be less than 20°, to facilitate closure reporting.|250x250px]]
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This section concerns the geometry of ramps at basic exits and entrances, which are the majority of use cases for ramps. For information on the geometry of other junctions involving ramps, see the other sections below.
  
: [[Image:Exit-ramp-geom.png]]
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When placing the beginning of an exit ramp, first place a [[geometry node]] of the ramp segment at the nearest point to the exit from among:
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* If there's no solid white line, at the gore point (where the painted lines diverge)
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* If there's a solid white line, at its beginning
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* The beginning of the inside solid white line on a multi-lane exit
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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
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Extend the ramp naturally to create a junction with the road segment at a 20° departure angle. This will allow for consistent timing of exit instructions and make it easier to report closures in the Waze client.
 +
[[File:ExitRampShort.png|900px]]
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At the end of an entrance ramp place a geometry node at the end of the solid white line and extend the ramp to join with the highway at a reasonable departure angle that follows the natural road geometry. The angle used should allow for smooth and consistent auto-zoom functionality—the client remains zoomed in for the duration of the ramp, zooming out when the user gets on the freeway.
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[[File:EntranceRamp.png|900px]]
  
Do the same when placing the end of a ramp. This will allow for consistent auto-zoom functionality – the client remains zoomed in for the duration of the ramp, zooming out when the user gets on the freeway.
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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 divide a ramp into multiple ramps.
  
: [[Image:Entrance-ramp-geom.png]]
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: [[File:Junction_style_simple_ramp_(2).PNG|400px]]
  
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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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.
  
: [[Image:Jct_ramp_no_split.png]]
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: [[File:Junction Style ramp split.PNG|350px]]
  
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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== {{anchor|Interchange types}}Component junction types ==
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Interchanges are made up of multiple individual junctions involving the following:
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* One or more highways, represented by the three highway road types {{Minor Highway}}, {{Major Highway}}, and {{Freeway}}
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* Grade-separated cross streets which may be highways or lower road types such as {{Primary Street}}
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* {{Ramp|Ramps}} to join them
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Specific examples of how to handle common junction types are provided in the following sections.  All of those examples use these road types. If you are unsure what road type you should use, refer to the [[road types]] article.
  
: [[Image:Jct_ramp_split.png]]
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=== {{anchor|Exits}}Basic exit/entrance ===
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A basic exit is a junction where a single ramp exits a highway and leads to another road, and the continuation of the highway is obvious to drivers. Most exits fit this description.
  
== Interchange types ==
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To map a basic exit:
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 entering segment and the continuing segment must be {{Freeway}}, {{Major Highway}}, or {{Minor Highway}} type and should match name and type.
 +
# The freeway/highway continuing segment should have close to a zero degree departure angle from the entering segment.
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# The exiting segment should be of the type {{Ramp}}.
 +
# The ramp geometry should be consistent with [[#Ramp geometry and complexity|ramp geometry and complexity]].
  
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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When those conditions are met and the ramp exits to the right, the navigation will present an "exit right" instruction when the ramp is to be used, and will remain silent when the continuing freeway/highway segment is to be used. When those conditions are met and the ramps exits to the left, the default instruction in the USA is "keep left." A [[Turn instruction override#Exit left|turn instruction override]] should be used to provide an "exit left" instruction at basic exits where the exit ramp departs the highway to the left.
  
If you are unsure what road type you should use, refer to the following pages for more information.
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Similarly, a basic entrance is where a single ramp joins an existing highway, and the path of the highway is obvious to drivers. The geometry of a basic entrance junction should be mapped just like a basic exit, but with directions reversed.
*[[Road_Types_(USA)|United States]]
 
*[[How_to_label_and_name_roads_%28United_Kingdom%29#Road_types|United Kingdom]]
 
  
=== Exits ===
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==== {{anchor|Exit geometry}}Basic exit geometry ====
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.
 
 
 
==== Exit geometry ====
 
 
: [[Image:Jct_fwy_exit.png]] [[Image:Jct_maj_exit.png]] [[Image:Jct_min_exit.png]]
 
: [[Image:Jct_fwy_exit.png]] [[Image:Jct_maj_exit.png]] [[Image:Jct_min_exit.png]]
  
To be treated as a basic Exit, the following must be true:
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See [[#Ramp geometry and complexity|ramp geometry and complexity]] for information on setting the angles of basic exits.
# The entering segment and one exiting segment must be one of the three Highway/Freeway types
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==== {{anchor|Exit naming}}Basic exit naming ====
# The Highway/Freeway exiting segment must have close to a zero degree departure angle from the entering segment
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The highway/freeway segments before and after the junction should be named the same. The ramp segments should be named in accordance with the section on [[Road names#Exit|exit ramp names]]. In addition, if an exit carries a concurrent route away from the highway, for example a US route 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.
# The other exiting segment must be of the type Ramp
 
# The Ramp exiting segment must have a departure angle of between 20 and 30 degrees from the entering segment
 
  
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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=== {{Anchor|Wayfinders|Terminology|Criteria|Configuration|Segment naming}}Complex exit ===
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A complex exit is a junction where one or more exit ramps leave the highway, and the continuation of the highway is not obvious to drivers. Therefore, another instruction is needed for traffic continuing on the highway. This can be a "keep" or "continue" instruction. When mapping complex exits, the geometry should match the instruction given, so for "continue" instructions the geometry should be set up as described for exits in [[#Ramp geometry and complexity|ramp geometry and complexity]], and for keep instructions (i.e. most wayfinder exits), the geometry should be set up in the same way as a [[#Freeway fork geometry|freeway fork]]. For criteria and further details on mapping complex exits, see [[wayfinder]] and [[turn instruction override]].
  
==== Exit naming ====
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=== {{anchor|Freeway/highway splits|Freeway/highway forks}}Freeway/highway fork===
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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A highway/freeway fork  is a junction where one freeway or highway splits into two, and there is no obvious straight through direction for a driver. This can happen at the end of a concurrency of highway routes or where one or both highway routes begin. This is synonymous with the MUTCD term "split."
  
[[Road names/USA#Exit_ramps_and_Entrance_ramps_.28on-ramps.29|US Specific Ramp Names]]
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==== {{anchor|Freeway split geometry}}Freeway fork geometry ====
 
 
[[How_to_label_and_name_roads_%28United_Kingdom%29#Ramps_.28to.2Ffrom_Motorways_and_Dual_Carriageways.29|UK Specific Ramp Names]]
 
 
 
[[Road types and names|Naming standards for other areas]]
 
 
 
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.
 
 
 
=== Freeway/highway splits ===
 
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. 
 
 
 
==== Freeway split geometry ====
 
 
: [[Image:Jct_fwy_fwy_split.png]]
 
: [[Image:Jct_fwy_fwy_split.png]]
  
To receive a navigation instruction for '''both''' branches of a split, the following must be true:
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Place the first geometry node of each outgoing segment at the beginning of the solid white line where the roadways diverge, then move the junction node to where each outgoing segment deviates from the incoming segment 20° right and left.
# All segments must be one of the three Highway/Freeway Types
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==== {{anchor|Freeway split naming}}Freeway fork naming====
# 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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The purpose of freeway fork naming is to give instructions for both right and left side of the fork that are accurate to posted signage. That can be accomplished using the following:
 +
# Signs and [[wayfinder]]<nowiki/> stub segments: If an outgoing segment has a big green sign (BGS) above it that says something different than the name of the entering segment, cut the segment at the fork to create a stub and name it according to what is on the sign. If the outgoing segment continues the route designation of the incoming segment, add that as an alternate name of the stub to preserve name continuity for [[Detour Prevention Mechanisms|detour prevention]] purposes. If the BGS doesn't say anything different from the name of the highway itself, there is no need to make a stub; simply name the outgoing segment with the name of the highway.
 +
# A [[turn instruction override]]: If one branch is named the same as the entering segment either as a primary or alt name, use a turn instruction override to give a "keep left" or "keep right" instruction depending upon which direction the branch leaves the fork.
 +
For further details on freeway fork mapping, see the [[wayfinder]] page.
  
==== Freeway split naming ====
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=== {{anchor|Ramp-ramp forks}}Ramp fork ===
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A ramp may itself fork and branch into two directions. This is synonymous with the MUTCD term "bifurcation." Most of the time a ramp fork should be mapped to give instructions to traffic going either direction. This is accomplished by using the ramp type for both outgoing segments and names that are different from the incoming segment or turn instruction overrides where necessary.
  
The primary rule is that all 3 segments at the junction must have different namesThat can be accomplished in one of two ways:
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==== Ramp fork geometry ====
# 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.
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[[Image:Jct_ramp_ramp_split.png]] [[Image:jct_cd_ramp_split.png]]
# 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]].
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 +
Ramp forks should generally have the same geometry as [[#Freeway fork geometry|freeway forks]], except for where the ramp fork is part of a [[#Collector/distributor cloverleaf|collector/distributor interchange]] or if one side of the ramp fork is using a "continue" instruction or no instruction. In this case the ramp fork should look more like a [[#Ramp geometry and complexity|basic exit]].
  
=== Wayfinders ===
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==== Ramp fork naming ====
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Naming of ramp forks should generally follow the guidelines from [[Road names#Exit|road names]], but there are multiple ways to handle all the signs present at each junction.
  
A '''wayfinder''' gives a user an instruction reminding them to stay on the road the user is already on, in situations where a reminder is warranted. A wayfinder is warranted in the following situations:
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===== Using information on the signs directly =====
* '''Lane drops''', where at least as many lanes leave the road as stay on the road;
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A simple way to name the ramp segments in ramp forks is to name each ramp segment with full or abbreviated information shown on the signs leading into it. This will provide a static set of instructions for users as they travel on each segment, regardless of what their further movements will be. This is especially appropriate when a single sign is present at an exit, but multiple signs with different information are present farther down the road.
* '''Non-obvious continuations''', where at least one "exit only" lane exists on the side of the road where exits are not normally placed (in a [[right-hand traffic]] country, exiting traffic is to the left and continuing traffic is to the right); and
 
* '''Inconsistent signage''', where a highway continues as a numbered route, but signs call it only by a name.
 
  
{{NeedImage| Need sample images for "lane drops" and "non-obvious continuations"; also, example of BGS with lane arrows}}
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===== Using road name inheritance =====
 +
[[File:RampforkMUTCD.png|thumb]]
  
In these cases, we need to use a wayfinder configuration. Each wayfinder configuration will have one "IN" segment and two "OUT" segments.
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Another way to name these ramp segments is to use name inheritance. If a ramp is unnamed ("no name" box checked), the name of a subsequent ramp on 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 only 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
 +
*# 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
 +
*# at the fork: keep left to Exit 36: I-17 N / Miami
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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.
  
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====== Name inheritance, but signage on consecutive signs are different ======
 +
[[File:PseudoWF.png|thumb]]
  
Keep these basic principles in mind:
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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:
* The OUT segments must be the same type (either Freeway or Ramp, as explained below).
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# Leave the exit ramp unnamed
* Each OUT segment must have a name different than the IN segment.
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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}}
* OUT segments should be named with the information displayed on the roadway signs.
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# Name the stub according to the sign at the ''exit''
** However, if this would leave an OUT segment with the same name as the IN segment, the OUT segment name must be modified.
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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
* Do '''not''' use "to" at the beginning of the name of the continuation segment (the user is already on the road, not going "to" it).
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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
* Each "stub" segment should be {{:Segment length/Minimum}} long. This is long enough so it will not cause routing problems, but it is short enough to suppress names (on Freeway stubs) and keep freeways looking contiguous (on Ramp stubs).
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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.
  
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== {{Anchor|Interchange configurations}}Configurations ==
  
To configure the wayfinder,
+
=== {{anchor|Diamond interchange}}Diamond ===
* If the numbered/signed exit is on the '''right''', the OUT segments should be {{Ramp}} type. This will give an "exit right" instruction for the exit and a "stay to the left" instruction for the continuation.
+
: [[File:Diamond interchange.PNG|750px]]
** For a basic [[Junction Style Guide/Interchanges#Exits|exit]], use a named Ramp stub for the continuation, and a standard Ramp for the exit.
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''See also: [[Wikipedia:Diamond_interchange|Diamond interchange article on Wikipedia]]''
** For a [[Junction Style Guide/Interchanges#Freeway.2Fhighway splits|freeway split]], use a Ramp stub on both sides.
 
* If the numbered/signed exit is on the '''left''', the OUT segments should be {{Freeway}} type. This will give "stay to the" instructions on both sides (if Ramp segments were used, Waze would give a confusing "exit right" instruction for the continuation).
 
** For a basic [[Junction Style Guide/Interchanges#Exits|exit]], use a named Freeway stub for the continuation, and an unnamed Freeway stub followed by a named Ramp for the exit.
 
** For a [[Junction Style Guide/Interchanges#Freeway.2Fhighway splits|freeway split]], use named Freeway stubs on both sides.
 
  
<div style="font-size:smaller">
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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.
{| class="wikitable"
 
|-
 
! Exit direction
 
! Type
 
! Left OUT configuration
 
! Right OUT configuration
 
! Example
 
|-
 
| Right
 
| Basic exit
 
| named Ramp stub → Fwy (continuation)
 
| named Ramp (exit)
 
| image
 
|-
 
| Right
 
| Fwy split
 
| named Ramp stub → Fwy (continuation)
 
| named Ramp stub → Fwy (exit)
 
| image
 
|-
 
| Left
 
| Basic exit
 
| unnamed Fwy stub → named Ramp (exit)
 
| named Fwy stub → Fwy (continuation)
 
| image
 
|-
 
| Left
 
| Fwy split
 
| named Fwy stub → Fwy (exit)
 
| named Fwy stub → Fwy (continuation)
 
| image
 
|}
 
</div>
 
  
=== Ramp-ramp splits ===
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In the simplest form, this can be represented as single connections from the ramps to the surface street.  
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_ramp_ramp_split.png]]
 
 
 
==== Ramp split naming ====
 
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.
 
 
 
'''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:
 
* 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.
 
 
 
'''Example of good use of unnamed ramps:'''
 
* 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:'''
 
* 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:'''
 
 
 
* Initial Exit Sign: Exit 70A-B to City A and City B
 
* 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 ==
+
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.
Please see the [[Limited_Access_Interchange_Style_Guide|Limited Access Interchange Style Guide]].
 
  
=== Diamond interchange ===
+
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_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_diamond_simple_turns_new.png]]
  
In the simplest form, this can be represented as single connections from the ramps to the surface street.
+
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.  
 
 
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.
 
 
 
: [[Image:Jct_diamond_simple_turns.png]]
 
 
 
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.  
 
  
 
First we see the turns that must be restricted for the exit ramps:
 
First we see the turns that must be restricted for the exit ramps:
  
: [[Image:Jct_diamond_cplx_turns_off_L.png]]  [[Image:Jct_diamond_cplx_turns_off_R.png]]
+
: [[Image:Jct_diamond_cplx_turns_off_L_new.png]]  [[Image:Jct_diamond_cplx_turns_off_R.png]]
  
 
Then we see what must be restricted for the entrance ramps:
 
Then we see what must be restricted for the entrance ramps:
Line 229: Line 153:
 
: [[Image:Jct_diamond_cplx_turns_on.png]]
 
: [[Image:Jct_diamond_cplx_turns_on.png]]
  
'''Note on elevations:'''
+
'''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.
 
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 ===
+
=== {{anchor|Cloverleaf interchange}}Cloverleaf ===
 
: [[Image:Jct_cloverleaf.png]]
 
: [[Image:Jct_cloverleaf.png]]
  
''See also: [http://en.wikipedia.org/wiki/Cloverleaf_interchange Cloverleaf Interchange article on Wikipedia]''
+
''See also: [[wikipedia:Cloverleaf_interchange|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.
+
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_cloverleaf_off_outer_turns.png]] [[Image:Jct_cloverleaf_off_inner_turns.png]]
 
: [[Image:Jct_cloverleaf_off_outer_turns.png]] [[Image:Jct_cloverleaf_off_inner_turns.png]]
Line 245: Line 169:
 
: [[Image:Jct_cloverleaf_on_turns.png]]
 
: [[Image:Jct_cloverleaf_on_turns.png]]
  
The connections to the Freeway segments may be treated in two ways:
+
The connections to the freeway segments may be treated in two ways:
  
 
:[[Image:Jct_cloverleaf_options.png]]
 
:[[Image:Jct_cloverleaf_options.png]]
  
# (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.
+
# (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.  
+
# (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.  
  
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.
+
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.
  
'''Note on Elevation:'''
+
'''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.
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 ===
+
=== {{anchor|Folded diamond interchange}}Folded diamond ===
 
: [[Image:Jct_folded_diamond.png]]
 
: [[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]''
+
''See also: Discussion of Folded Diamonds and A2/B2 Partial Cloverleafs on the [[wikipedia: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.
+
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 us to easily restrict the illegal and usually impossible ramp-to-ramp movement.
+
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.
  
 
: [[Image:Jct_folded_diamond_u-turn.png]]'
 
: [[Image: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 article [[Junction_Style_Guide#How_complex_should_ramps_be?|How complex should ramps be?]] in the Junction Style Guide.  
+
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.  
  
 
Restrict all non-permitted turns.
 
Restrict all non-permitted turns.
Line 273: Line 196:
 
: [[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_folded_diamond_off_turns_L.png]] [[Image:Jct_folded_diamond_off_turns_R.png]] [[Image: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.
+
'''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) ===
 
=== Single-point urban interchange (SPUI) ===
: [[Image:Jct_SPUI.png]]
+
: [[File:SPUI.PNG|750px]]
''See also: [http://en.wikipedia.org/wiki/Single-point_urban_interchange Single Point Urban Interchange article on Wikipedia]''
+
''See also: [[wikipedia: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.
 
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 very much like in the case of a diamond interchange:
+
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:
  
: [[Image:Jct_SPUI_off_outer_turn.png]]
+
: [[File:SPUI outer branch.PNG|500px]]
  
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.
+
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.
  
: [[Image:Jct_SPUI_off_inner_turn.png]]
+
: [[File:SPUI inner branch.PNG|700px]]
  
 
Luckily the entrance ramp restrictions are similar to the diamond interchange:
 
Luckily the entrance ramp restrictions are similar to the diamond interchange:
  
: [[Image:Jct_SPUI_on_turn.png]]
+
: [[File:SPUI middle branch.PNG|400px]]
  
 
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.
 
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.
  
: [[Image:Jct_SPUI_all_turns.png]]
+
: [[File:SPUI disabled turns.PNG|300px]]
  
'''Note on Elevation:'''
+
'''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.
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 lanes ===
+
=== {{Anchor|Collector/Distributor Lanes}}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.
+
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:
 
Collector/distributor lanes serve as either:
Line 309: Line 231:
  
  
==== Collector/distributor interchanges ====
+
==== {{anchor|Collector/distributor interchanges}}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.
 
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.
Line 319: Line 241:
 
[[Image:Jct_fc_cloverleaf_bad.png]]
 
[[Image:Jct_fc_cloverleaf_bad.png]]
  
The [[Detour Prevention Mechanisms|detour prevention mechanism]] will prevent Waze from routing users onto the collector-distributor and back onto the freeway – as long as the city name on the freeway is the same (or set to "no city") 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.
+
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.
  
==== Complex collector/distributor interchanges ====
+
==== {{anchor|Complex collector/distributor interchanges}}Complex collector/distributor interchange ====
  
 
[[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)]]
 
[[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)]]
Line 327: Line 249:
 
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.
 
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 the city 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.
+
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.
  
 
{{clear}}
 
{{clear}}
Line 340: Line 262:
  
 
Where collector/distributor lanes are used as part of a local-express lane configuration,
 
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
+
*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" (and "I-96 Express W" for the Express lanes).
+
*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).
  
 
{{clear}}
 
{{clear}}
 +
 +
=== {{Anchor|
 +
Diverging diamond interchange (DDI)|Diverging diamond interchange|Diverging_diamond_interchange|DDI}}Diverging diamond (DDI) ===
 +
 +
''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.
 +
 +
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 ====
 +
[[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}}
 +
==== 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.[[File:DDI Example Dupont - turn restrictions.png|thumb|871x871px|All restricted turns within a DDI (displayed by using Shift+Z).|none]]
 +
 +
====== 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.
 +
 +
====== 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.
  
 
== See also ==
 
== See also ==
  
Review the [http://en.wikipedia.org/wiki/Interchange_(road) Wikipedia article on Road Interchanges] for further information on this topic.
+
Review the [[Wikipedia:Interchange_(road)|Wikipedia article on road Interchanges]] for further information on this topic.
 +
 
 +
{{ReturnTo | Junction_Style_Guide | the Junction Style Guide}}
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[[Category:Style Guides]]

Latest revision as of 01:16, 21 March 2019

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:

Ramp geometry and complexity

Divergence is 12.5° on the left and 22.5° on the right. No angle between outgoing segments should ever be less than 20°, to facilitate closure reporting.

This section concerns the geometry of ramps at basic exits and entrances, which are the majority of use cases for ramps. For information on the geometry of other junctions involving ramps, see the other sections below.

When placing the beginning of an exit ramp, first place a geometry node of the ramp segment at the nearest point to the exit from among:

  • If there's no solid white line, at the gore point (where the painted lines diverge)
  • If there's a solid white line, at its beginning
  • The beginning of the inside solid white line on a multi-lane exit
  • 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

Extend the ramp naturally to create a junction with the road segment at a 20° departure angle. This will allow for consistent timing of exit instructions and make it easier to report closures in the Waze client. ExitRampShort.png At the end of an entrance ramp place a geometry node at the end of the solid white line and extend the ramp to join with the highway at a reasonable departure angle that follows the natural road geometry. The angle used should allow for smooth and consistent auto-zoom functionality—the client remains zoomed in for the duration of the ramp, zooming out when the user gets on the freeway. EntranceRamp.png

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 divide a ramp into multiple ramps.

Junction style simple ramp (2).PNG

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.

Junction Style ramp split.PNG

Component junction types

Interchanges are made up of multiple individual junctions involving the following:

  • One or more highways, represented by the three highway road types  Minor Highway ,  Major Highway , and  Freeway 
  • Grade-separated cross streets which may be highways or lower road types such as  Primary Street 
  •  Ramps  to join them

Specific examples of how to handle common junction types are provided in the following sections. All of those examples use these road types. If you are unsure what road type you should use, refer to the road types article.

Basic exit/entrance

A basic exit is a junction where a single ramp exits a highway and leads to another road, and the continuation of the highway is obvious to drivers. Most exits fit this description.

To map a basic exit:

  1. The entering segment and the continuing segment must be  Freeway ,  Major Highway , or  Minor Highway  type and should match name and type.
  2. The freeway/highway continuing segment should have close to a zero degree departure angle from the entering segment.
  3. The exiting segment should be of the type  Ramp .
  4. The ramp geometry should be consistent with ramp geometry and complexity.

When those conditions are met and the ramp exits to the right, the navigation will present an "exit right" instruction when the ramp is to be used, and will remain silent when the continuing freeway/highway segment is to be used. When those conditions are met and the ramps exits to the left, the default instruction in the USA is "keep left." A turn instruction override should be used to provide an "exit left" instruction at basic exits where the exit ramp departs the highway to the left.

Similarly, a basic entrance is where a single ramp joins an existing highway, and the path of the highway is obvious to drivers. The geometry of a basic entrance junction should be mapped just like a basic exit, but with directions reversed.

Basic exit geometry

Jct fwy exit.png Jct maj exit.png Jct min exit.png

See ramp geometry and complexity for information on setting the angles of basic exits.

Basic exit naming

The highway/freeway segments before and after the junction should be named the same. The ramp segments should be named in accordance with the section on exit ramp names. In addition, if an exit carries a concurrent route away from the highway, for example a US route 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.

Complex exit

A complex exit is a junction where one or more exit ramps leave the highway, and the continuation of the highway is not obvious to drivers. Therefore, another instruction is needed for traffic continuing on the highway. This can be a "keep" or "continue" instruction. When mapping complex exits, the geometry should match the instruction given, so for "continue" instructions the geometry should be set up as described for exits in ramp geometry and complexity, and for keep instructions (i.e. most wayfinder exits), the geometry should be set up in the same way as a freeway fork. For criteria and further details on mapping complex exits, see wayfinder and turn instruction override.

Freeway/highway fork

A highway/freeway fork is a junction where one freeway or highway splits into two, and there is no obvious straight through direction for a driver. This can happen at the end of a concurrency of highway routes or where one or both highway routes begin. This is synonymous with the MUTCD term "split."

Freeway fork geometry

Jct fwy fwy split.png

Place the first geometry node of each outgoing segment at the beginning of the solid white line where the roadways diverge, then move the junction node to where each outgoing segment deviates from the incoming segment 20° right and left.

Freeway fork naming

The purpose of freeway fork naming is to give instructions for both right and left side of the fork that are accurate to posted signage. That can be accomplished using the following:

  1. Signs and wayfinder stub segments: If an outgoing segment has a big green sign (BGS) above it that says something different than the name of the entering segment, cut the segment at the fork to create a stub and name it according to what is on the sign. If the outgoing segment continues the route designation of the incoming segment, add that as an alternate name of the stub to preserve name continuity for detour prevention purposes. If the BGS doesn't say anything different from the name of the highway itself, there is no need to make a stub; simply name the outgoing segment with the name of the highway.
  2. A turn instruction override: If one branch is named the same as the entering segment either as a primary or alt name, use a turn instruction override to give a "keep left" or "keep right" instruction depending upon which direction the branch leaves the fork.

For further details on freeway fork mapping, see the wayfinder page.

Ramp fork

A ramp may itself fork and branch into two directions. This is synonymous with the MUTCD term "bifurcation." Most of the time a ramp fork should be mapped to give instructions to traffic going either direction. This is accomplished by using the ramp type for both outgoing segments and names that are different from the incoming segment or turn instruction overrides where necessary.

Ramp fork geometry

Jct ramp ramp split.png Jct cd ramp split.png

Ramp forks should generally have the same geometry as freeway forks, except for where the ramp fork is part of a collector/distributor interchange or if one side of the ramp fork is using a "continue" instruction or no instruction. In this case the ramp fork should look more like a basic exit.

Ramp fork naming

Naming of ramp forks should generally follow the guidelines from road names, but there are multiple ways to handle all the signs present at each junction.

Using information on the signs directly

A simple way to name the ramp segments in ramp forks is to name each ramp segment with full or abbreviated information shown on the signs leading into it. This will provide a static set of instructions for users as they travel on each segment, regardless of what their further movements will be. This is especially appropriate when a single sign is present at an exit, but multiple signs with different information are present farther down the road.

Using road name inheritance
RampforkMUTCD.png

Another way to name these ramp segments is to use name inheritance. If a ramp is unnamed ("no name" box checked), the name of a subsequent ramp on 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 only 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.

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.