Difference between revisions of "Roundabout"

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====Segment angles====
 
====Segment angles====
[[File:RABent.png|alt=|right|262x262px]]
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[[File:RABent1.png|frameless|left]]
[[File:RAStraight.png|alt=|left|262x262px]]
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[[File:RAStraight1.png|frameless|right]]
 
Since the angles of the segments approaching the nodes do not matter, both of these layouts will give the same instructions. Only the angles between the nodes and the center of the roundabout (roundabout angles) determine which instructions are given.{{Clear}}
 
Since the angles of the segments approaching the nodes do not matter, both of these layouts will give the same instructions. Only the angles between the nodes and the center of the roundabout (roundabout angles) determine which instructions are given.{{Clear}}
 
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====Three incoming segments====
 
====Three incoming segments====
 
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[[File:RANormal1.png|thumb|Both exit nodes have roundabout angles within the normal range of ±15° from 0° or 90°.|alt=]]'''Let's assume this roundabout has a radius of less than 25 meters, so the other criteria are met for normal instructions.'''
*'''Let's assume this roundabout has a radius of less than 25 meters, so the other criteria are met for normal instructions.'''
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'''Coming from node #1, this is how we see the roundabout:'''
*'''Coming from node #1, this is how we see the roundabout:'''
 
 
 
[[File:RANormal.png|thumb|295x295px|Both exit nodes have roundabout angles within the normal range of ±15° from 0° or 90°.|alt=]]
 
<br />
 
 
 
 
:*Both exits 2 and 3 have roundabout angles within the normal range (90&deg;&plusmn;15&#176; & 0&deg;&plusmn;15&deg;).
 
:*Both exits 2 and 3 have roundabout angles within the normal range (90&deg;&plusmn;15&#176; & 0&deg;&plusmn;15&deg;).
 
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:*''These exits will get an instruction to "turn right" or "continue straight".''
 
:*''These exits will get an instruction to "turn right" or "continue straight".''
 
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{{clear}}
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[[File:RANNormal1.png|thumb|Node 2 has a roundabout angle that is outside the normal range of ±15° from 90°|alt=]]
 
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'''Coming from node #3, this is how we see the roundabout:'''
*'''Coming from node #3, this is how we see the roundabout:'''
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:*Exit 1 is within the normal roundabout angle range, but exit 2 is not within the normal roundabout angle range.
 
 
[[File:RANNormal.png|thumb|295x295px|Node 2 has a roundabout angle that is outside the normal range of ±15° from 90°|alt=]]
 
<br />
 
 
 
:*Exit 1 is within the normal roundabout angle range, but exit 2 is not within the normal roundabout angle range. <br />
 
 
:*''Even though one of these exits is within normal range, the roundabout itself is ‘non-normal’ and both exits will get the "take the X exit" prompt. All exits must be within the normal range with respect to a given entrance in order to generate "turn left", "turn right", "continue straight" or "make a U-turn" instructions from this entrance.''
 
:*''Even though one of these exits is within normal range, the roundabout itself is ‘non-normal’ and both exits will get the "take the X exit" prompt. All exits must be within the normal range with respect to a given entrance in order to generate "turn left", "turn right", "continue straight" or "make a U-turn" instructions from this entrance.''
 
 
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Revision as of 17:28, 10 August 2021

Roundabouts, rotaries, or traffic circles, are unique segments of roadway in the Waze routing system. When a driver approaches a roundabout, a specific icon is displayed in the turn direction area of the display with a number corresponding to the exit count from the driver's entry into the roundabout or with a symbol of the movement through the roundabout. Manually creating a circular road will not produce these instructions.

What is a roundabout and what is not

In general when there is a clear roundabout in imagery, it is best to have it mapped as a roundabout in the road layer. There are a few cases that should not be mapped as roundabouts.

These are not drawn as roundabouts
Description Image
Streets intersect, but there is no center island preventing left turns. There are no signs indicating a roundabout approaching the intersection or painted on the ground. RdAbt-Not1.png
A single road segment leading to a cul-de-sac should be drawn as a dead end. With very large roads it might be advisable to create a three-segment loop but not a roundabout. Jct cul-de-sac island ex.png
Small traffic-calming circles are usually not drawn as roundabouts, especially if they do not increase the size of the intersection greater than that of a simple four-way intersection, have no roundabout signs or yield signs and have stop signs on at least one approach. Check with local leadership on how to map traffic circles. TrafficCircleSquare.png

Creation from an intersection

Oftentimes when streets become more congested, planners will install a roundabout to get traffic to flow more freely. This section shows the steps to get from an existing intersection to a new roundabout.

The situation starts out like this, where the roads are no longer aligned with the new plan, and now there is a roundabout which we need to create. This situation is fairly simple because all the segments are connected together already.

First, move the junction to the center of the roundabout. Click and drag the junction to where it should be. We also need to adjust the incoming segments so that they align with the roads leading into the roundabout. When roundabouts are built at existing intersections, the approaching segments are usually realigned for drivers to reach optimal speeds when entering and exiting the roundabout and/or to allow the roundabout to be placed at appropriate distances from existing structures. If roads have been added, removed or reconfigured in other ways near the roundabout, make these changes now.

Oftentimes roundabouts are completed before aerial imagery is updated. In these cases, enable the GPS tracks layer in the map editor by pressing Shift+G, and use the tracks to guide your preparations. If the roads approaching the roundabout meet the criteria for dividing roads, make the roads divided where they will connect to the roundabout. Note that where road changes do not match aerial imagery, leaving a map comment is advised.

Once all preparations are made, hover the cursor over the Roads icon on the toolbar and click Roundabout. You can also use the keyboard shortcut O.

Move the cursor to the center of the actual roundabout. The cursor will be a crosshair + to indicate it is in roundabout creation mode. Click once at the center and then move the mouse any direction towards the perimeter of the roundabout. An orange circle will grow and shrink as you move the mouse, and the numbers in the center of the circle display the radius of the resulting roundabout.

Click once when satisfied with the size and shape of the roundabout, which will create new 1-way segments in between each road segment contacted by the edge of the orange circle. Each of those segments is disconnected from the junction in the center and reconnected to the roundabout with allowed turns already set.

Any segments completely within the roundabout area will be deleted.

Just as with drawing new roads, the segments of the roundabout which were created in the last step must be confirmed. That is, each segment needs the country, state and city. Please see the updating details to confirm the road section for details on this process. If the roundabout doesn't have a name, which is usually the case, click the None box next the Street. If the roundabout is a named circle on local signs, its segments can be named just like any other road. This is particularly important if addresses are on the roundabout. If this roundabout is a local landmark, such as Dupont Circle in Washington, DC, an area place may also be drawn inside it with the Park and/or Junction/Interchange categories, as appropriate.

When the process is complete and the Save button has been clicked on one last time, this is how the new roundabout looks.

Some new roundabouts may be announced by local authorities before their construction, complete with road closures. If this is the case, map the roundabout in this way while following the procedures outlined for scheduled reconfigurations.

For further reference, please watch this video on roundabout creation.

Oval, large or unusual shapes

This roundabout is shaped like a peanut; it was created with the roundabout tool and then manually squished into this shape. It has closures scheduled to end when it opens to traffic.

If an oval or elliptical roundabout is required, hold down the Shift key during roundabout creation. At this time only oval roundabouts along the north/south or east/west axis can be created. If an alternate shape or axis is desired, create a circular roundabout that is close to the correct shape and adjust the geometry handles manually.

Note that roundabouts cannot be created over a maximum of 100 m (328 feet) in radius because of the danger that erasing all roads in the center could accidentally wipe out an entire city of roads. If a larger radius is required, use the same steps described above to alter the shape by adjusting the nodes as required.

Scheduled creation

In areas where local government is proactive in announcing traffic changes, we may be able to map a roundabout before it opens and use closures to open it on time. This usually happens as an improvement to an existing intersection, with the intersection closed during roundabout construction. To do this:

  1. Add necessary road closures during construction. If only the intersection is closed where the roundabout is being constructed, make a single one-way closure leading away from this intersection, and close the node.
  2. Once road closures are active, restrict all turns represented by the closures and wait for a tile update.
  3. Build the roundabout according the section above, adding time-based restrictions to end sometime before its scheduled opening, and wait for a tile update.
  4. Add closures on the roundabout scheduled to end when the roundabout opens, and remove the time-based restrictions. Attach these closures to an event in order to announce the imminent opening of the new roundabout.

The procedure is similar to the general procedure for scheduled reconfigurations with some important differences:

  • A new roundabout at an existing intersection is mapped after closures begin, since the creation of a roundabout deletes roads inside it, making it difficult to preserve routing before construction begins.
  • Creation of a roundabout preserves the segment IDs of roads leading into it. Therefore, steps 2 and 3 can be combined in a quicker, slightly riskier process, by removing the construction closures at the roundabout, building the roundabout, then adding the closures back with an end time within 48 hours. After a tile update, the closures can be removed from the approach roads and applied to the roundabout (step 4).
    • Only one tile update is necessary, so the process is quicker.
    • There is a risk of people being routed through the closed intersection as the roundabout is being built in the editor, and there is another risk of a tile delay making it difficult to preserve closures.

Improving manually drawn roundabouts

If normal one-way segments are drawn in a circle, Waze will not navigate them like a roundabout, instead producing "turn right and then turn right" instructions. This is not what the driver would expect. Therefore, such a roundabout should be redrawn.

The first step is to select and delete all the segments that make up the circle connecting the roads leading into the roundabout. That can be done individually or as a group.

Next, extend the segments deeper into the center of the roundabout area. They need to end inside the final perimeter of the roundabout, otherwise they will not be connected automatically during the final step of creating the roundabout. During this step be sure to center the roadway segments from the middle of their respective roads. Unless the actual road has a significant divider between the incoming and outgoing lanes on a road, avoid creating two separate one-way roads leading into and out of the roundabout (see below). Press Save to ensure there are no errors before going to the next step. After this, create the roundabout according to the section above.

Creating a roundabout from nothing

Draw all of the road segments that will lead to the roundabout and ensure they extend into the center of the roundabout area. Use the visual map to align the roads. From there, create the roundabout just as is described in the two sections above.

Note that there must be at least one road segment partially inside the area of the roundabout being created, otherwise no roundabout will be created.

Road type

It is possible to have multiple types of roads ( Street ,  Primary Street ,  Minor Highway , etc.) meeting at a roundabout.

To minimize inefficient routing, it is important to be careful with the road type assigned to the Roundabout itself. Any routing penalty going from connected roads to the roundabout must be kept to a minimum, but it should not be too "attractive" where routing through it is encouraged when unnecessary.

The road types of interest in are, in order from highest to lowest,  Freeway ,  Major Highway ,  Minor Highway ,  Primary Street ,  Street ,  Parking Lot Road , and  Private Road . Since a Roundabout is not a Limited Access Interchange, two Freeways should never meet at a roundabout; however, it is conceivable that a Freeway might begin or end at one.

To determine what road type to use for the Roundabout:

  1. Identify the two connected segments with the highest type listed above:
    • If a particular road goes through a roundabout, count the road as two separate segments, one on each side of the roundabout.
    • If a road on one side of the roundabout is a divided roadway made of two one-way road segments, count the pair of one-way segments as a single segment.
    • The two connected segments with the highest type may have the same type or different types.
    • If a ramp connects to the Roundabout, use the road type to which that ramp connects.
  2. Select the roundabout and set the road type as follows.
    • If the two highest-type segments have the same type, use that type.
    • If the two highest-type segments have different types, use the lower type of those two segments.
Roundabout Road Type Guide
Description Top 2 Road Types
RA Type
Example
A Primary Street and a Street cross at a Roundabout so we have two Street segments connected and two Primary Street segments connected.  Primary Street 

 Primary Street 

RdAbt PrPr.png
One Primary Street segment and three Street segments meet.  Primary Street 

 Street 

RdAbt PrSt.png
Three Primary Street segments and one Street segment meet.  Primary Street 

 Primary Street 

RdAbt PrPr3.png
A Major Highway and a Minor Highway cross so we have two segments of each type.  Major Highway 

 Major Highway 

RdAbt MjMj.png
Three Major Highway segments and one Minor Highway segment meet.  Major Highway 

 Major Highway 

RdAbt MjMj3.png
A Major Highway, two Primary Streets, and one Street segment meet. (The Major Highway can be thought to start/end at the Roundabout.)  Major Highway 

 Primary Street 

RdAbt MjPr.png
A Major Highway, a Primary Street, and two Street segments meet at a Roundabout.  Major Highway 

 Primary Street 

RdAbt MjPr2.png
A Major Highway, a Minor Highway, and two Primary Street segments meet. (If we used Primary Street, routing would be penalized going from the Minor Highway to the Major Highway.)  Major Highway 

 Minor Highway 

RdAbt MjMn.png
Same as above, except the Major Highway and Minor Highway are divided roadways. (Recall that a divided roadway is treated as one "segment" for this rule.)  Major Highway 

 Minor Highway 

Roundabout - split roads.png
A Ramp (connected to a Major Highway), a Minor Highway, and two Primary Street segments meet. (Recall that the type connected to the ramp is used in the analysis. Effectively, it's the same as the previous two examples.)  Major Highway 

 Minor Highway 

Roundabout - ramp.png
Only Ramp segments are connected to a Roundabout. If every segment connected is a Ramp, so is the Roundabout. (When only Ramps connect to a Roundabout, none of the connected road types are considered.)  Ramp  Roundabout - all ramps.png

Understanding navigation instructions

Waze supports two different styles of roundabout navigation instructions. One style instructs simply to turn or continue at the roundabout, while the other instructs how many exits one must pass before leaving the roundabout. The US editing community terms these two instruction styles as "normal" and "non-normal" respectively. The term "normal" is used here in its mathematical sense to mean "orthogonal", "perpendicular", or "at right angles".

This section will explain the difference between a normal and a non-normal roundabout.
Normal roundabouts:

Non-normal roundabouts:

  • Require at least one of the following:
    • 5 or more nodes.
    • Nodes outside the normal roundabout angle range
    • A radius greater than 25 meters.
  • Provide the following instructions:

A roundabout can be both normal and non-normal at the same time depending on your entry node, because the roundabout angle is calculated from where one enters the roundabout.

Roundabout angle

The roundabout angle is the angle of any segment connected to the roundabout from the perspective of the origin. This is basically the same as the central angle of a circle. The actual turn angle of the segments is irrelevant.
To explain;

  • Draw an imaginary line through the center of the roundabout to the other side of the roundabout from junction node where the origin joins the roundabout. This will represent a 0° roundabout angle, any deviation to the right or left will increase the angle.
  • Draw another imaginary line across the roundabout through the center and perpendicular to the first imaginary line. This will represent a 90° roundabout angle to either side.
Roundabouts
Normal Non-normal
Roundabout 3 normal.png

Roundabout 3 non-normal.png

All other segments are within the allowed ±15° from either 0° or 90°. Not all other segments are within the allowed ±15° from either 0° or 90°.

Examples

Segment angles

RABent1.png
RAStraight1.png

Since the angles of the segments approaching the nodes do not matter, both of these layouts will give the same instructions. Only the angles between the nodes and the center of the roundabout (roundabout angles) determine which instructions are given.


Three incoming segments

Both exit nodes have roundabout angles within the normal range of ±15° from 0° or 90°.

Let's assume this roundabout has a radius of less than 25 meters, so the other criteria are met for normal instructions.

Coming from node #1, this is how we see the roundabout:

  • Both exits 2 and 3 have roundabout angles within the normal range (90°±15° & 0°±15°).
  • These exits will get an instruction to "turn right" or "continue straight".
Node 2 has a roundabout angle that is outside the normal range of ±15° from 90°

Coming from node #3, this is how we see the roundabout:

  • Exit 1 is within the normal roundabout angle range, but exit 2 is not within the normal roundabout angle range.
  • Even though one of these exits is within normal range, the roundabout itself is ‘non-normal’ and both exits will get the "take the X exit" prompt. All exits must be within the normal range with respect to a given entrance in order to generate "turn left", "turn right", "continue straight" or "make a U-turn" instructions from this entrance.


Entries and exits

RdAbt-NoDivRd.png
RdAbt-DivRd.png

If the road segments approaching a roundabout do not meet the criteria for dividing roads, they are generally drawn as simple two-way roads connected perpendicular (90 degrees) to the roundabout circle itself. If they do meet the criteria for dividing, each entry or exit segment should be connected to its own node on the roundabout, and the segments should be drawn in a way that fits with the natural flow of traffic. This will almost always cause the roundabout instructions to be non-normal. Due to historical reasons, some regions of the USA have a preponderance of normal or non-normal roundabouts, and the users in those regions are accustomed to one or the other set of instructions. Check with your regional leadership to determine which instructions are preferred when drawing roundabouts.

Multiple segments at one node

It is usually inappropriate to join two segments at the same node on a roundabout and tends to cause problems. If both segments are one way in opposing directions, and the exit is to the left of the entrance, such as with both roadways of a divided highway, these will be treated correctly like a single two-way segment in navigation instructions. However, this geometry results in sharp turns that rarely fit the natural flow of traffic turning into and out of the roundabout, and it is often better simply to join each one-way segment at its own node on a roundabout.

Do not connect an entry belonging to one road to or past an exit belonging to the next road to the right, as this causes the first exit not to be counted and the subsequent exits to be numbered incorrectly. Even if the movement into and out of the roundabout is prohibited at this point (often the case in roundabouts with bypasses), if it is physically possible, users will tend to count it as the first exit, and we need to provide a consistent experience when mapping.

Do not connect more than one exit (either two-way segments or outgoing one-way segments) to the same node at a roundabout, as this causes Waze not to number any exit. In these cases Waze will show an empty circle for the roundabout instruction and will truncate the spoken instruction to "at the roundabout."

Moving junctions and disconnecting roads

When adjusting roundabouts, drag the junction nodes and move/delete the geometry points of the segments. This is better than disconnecting and reconnecting. Apart from the loss of turn data that happens with disconnections, some nodes can't be deleted from roundabouts, and changing segment IDs within them (caused by cutting and merging) has historically caused them to work improperly, though this may no longer be the case as of 2021. The script WME RA Util makes adjustment of roundabouts much easier.

Bypass

Some roundabouts are designed with physically separated bypass roads or at-grade connectors (AGCs). In many cases, roundabout bypasses can be mapped just like any other, but some roundabouts with bypasses have persistent routing problems.

Correcting inappropriate avoidance of roundabout bypasses

Where bypasses have been built to allow right-turning or straight traffic to avoid the roundabout altogether, Waze might send traffic through the roundabout anyway. This is often confusing to drivers when it is contrary to regulatory or informative signs. In these cases, use a junction box to restrict the invalid route through the roundabout, which will force the bypass to be routed.

What not to do

Entrances of one road connected to exits of a different road at the same nodes give incorrect normal instructions (left). Entrances of one road connected past exits of the next road give incorrectly numbered non-normal instructions (right).
Hacks to activate the U-turn penalty (left) and the detour prevention penalty (right) should no longer be used.

Before junction boxes were developed to work with roundabouts, various hacks were used to force bypass routing. Some involved connecting the entrance of one road at or past the exit of the next road, in order to prevent the redundant turn through the roundabout and force routing through the bypass. Others involved the activation of penalties on the redundant turn to force routing through the bypass. None of these should be used.

  • Do not junction the incoming and outgoing segment at the same node in order to prevent the redundant turn. Joining multiple entrances or exits at one node causes incorrect exit numbering, and, in some cases the distortion can cause incorrect normal instructions, (for example - "at the roundabout, turn right" to users continuing straight, if they travel through only 90° of the roundabout from entry to exit).
  • Do not move the incoming segment after the outgoing segment to make Waze avoid the exit. This is also a distortion if the roundabout and can cause incorrect roundabout instructions.
  • Do not activate fake U-turn and detour penalties by means of unconventional road names and types or unnatural geometry.

Wherever found, these deviations should be removed and replaced with junction boxes as described in the next section.

Junction box

A junction box has been used to force right turning traffic on US-41 S to use the bypass rather than being routed through the roundabout. Normal turn instructions have also been specified in accordance with regional norms, lane markings and signage

Junction boxes can be used over roundabouts, covering them either partially or fully. In addition to providing better timing, using a junction box on a roundabout can accomplish these goals:

  1. As mentioned above, they may be used to correct routing problems.
  2. They may also be used to override the default navigation instructions.
    • For example, divided roads may meet at a small roundabout, where drivers would expect normal instructions based on signs, lane markings and what's common in the region. Rather than using unnatural geometry to force the normal instructions, draw a junction box to encircle the roundabout and set the voice prompt for each path through the roundabout to Turn left, Turn right, U-turn or Continue.
    • Conversely, where non-normal instructions are desired that would otherwise be normal, make a junction box voice prompt of Let Waze count the exit number.
    • Furthermore, where small traffic-calming circles have been mapped as roundabouts, a junction box may be used to suppress unnecessary "at the roundabout, continue straight" instructions. Check with local leadership on how to handle traffic-calming circles.

If the junction box completely contains only nodes on the roundabout, its voice prompts will produce the proper roundabout spoken and visual instructions, such as "at the roundabout, turn right" and "at the roundabout, take the fourth exit". Normal and non-normal instructions can be used in the same roundabout. If nodes outside the roundabout are included in the junction box, the navigation instructions will not work as expected, so be sure to only include roundabout segments when using a junction box to control roundabout instructions.