Junction boxes

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Revision as of 01:28, 26 September 2021 by LostInMyMaps (talk | contribs) (Add an extra example of a complex intersection)

In line with our Revised Waze Editing Philosophy, our mapping standards have changed in 2020. For more information, see new technology, new mapping standards.

Introduction

Australia has spent years using workarounds to avoid using junction boxes (JBs), but those times must end. Many intersections around our country would benefit from a junction box, but it takes an educated and fearless editor to realise it.

This page will discuss common intersections that are important to have junction boxes in Australia. The USA wiki page has an amazing explanation of how junction boxes work and is highly recommended reading to understand the fundamentals of why junction boxes are so important to Waze.

Quickly, what’s a junction box do?

Remember that Waze stores data about segment and junction node traversal times? It does not further consider the relationship between segments around it beyond that they are connected. Junction boxes tell the Waze routing server that a group of segments are important together and that traversing a path through them should be considered a single intersection. This allows Waze to make more intelligent decisions about routing.

Junction boxes also allow for the fine control of paths through them, such as disabling a path that would otherwise be allowed through turn restrictions, or overriding turn instructions on paths instead of individual turns on segments within the junction box.

Limitations

Unfortunately these amazing and powerful tools have some limitations that you should be aware of before you go designing a complex intersection that requires them:

  • Minimum lock level
  • Maximum size
    • A junction box cannot exceed 0.01° latitude and 0.01° longitude. That’s pretty massive, and you’re unlikely to reach it.
  • Minimum two junction nodes
    • A junction box must include at least two junction nodes which must be connected by a segment.
  • No overlapping
    • A junction node cannot be included in multiple junction boxes.
  • Maximum 16 paths
    • No more than 16 controllable entry/exit paths can pass through a single-junction node within a junction box. Adjacent connections not displayed in the routing box list are also counted.
  • Enabled u-turn on a two-way segment
    • Having u-turns enabled on a two-way segment increases the number of paths.
  • Non-navigable segments
    • Junction nodes within a junction box can't be connected to non-drivable road types unless connected by a virtual node.

Junction boxes also create new limitations that need to be considered. Once applied to an intersection, editors must delete the junction box before they can:

  • Change direction of travel (two way/one way)
  • Move a junction node across the boundary of the junction box
  • Add/delete a junction node inside the junction box
  • Add/delete/connect/disconnect a segment inside a junction box

Deleting a junction box to perform any of the above also results in the loss of all the settings attached to it - so make a note before you blindly delete any!

Where junction boxes help

H-intersection with only one allowed u-turn

There is no way to allow u-turns in one direction and not another in a H-intersection using just segment turn restrictions. The fine control of this junction box allowed paths through it to be turned on or off to meet the unique requirements of the intersection.

This type of u-turn situation is common in states like Queensland and Victoria, and is rare in other states and territories.

Control u-turns one way while allowing the other with a junction box.

Allow u-turns when median segments is less than 14m

With a median segment 14m and less, the automatic u-turn prevention mechanism kicks in and prohibits the routing server from offering a u-turn even if it is allowed by the segment turn restrictions. A junction box when applied to an intersection automatically allows all routes not prohibited by segment turn restrictions, even overriding u-turn prevention.

This type of u-turn situation is common in states like Queensland and Victoria, and is rare in other states and territories.

Intersections with smaller medians are protected by automatic u-turn prevention unless you use a junction box.

Disable u-turns when median segments is greater than 14m

With median segments greater than 14m, the automatic u-turn prevention mechanism does not apply and Waze will offer a u-turn at an intersection like the following unless a junction box is applied and the paths disabled.

This type of u-turn situation is common in states like New South Wales where u-turns at traffic lights are not allowed. Other states and territories may encounter situations where there is a combination of allowed and disallowed u-turns, which can be easily controlled with a junction box.

Intersections with larger medians are NOT protected by automatic u-turn prevention when you might expect it to. Control turns with a junction box.
If you forget to add a junction box and disable u-turns on intersections with medians larger than 14m, you're going to get some grumpy Update Requests from users.


Queued traffic through multiple junction nodes from while waiting at an intersection

Particularly during busy periods, it is important to users that Waze gives them the best route. To do this, Waze needs to understand the speed traffic is traversing segments and junction nodes. It has no understanding though that traffic queuing across multiple segments might be related unless we tell it with a junction box.

Consider the following example where the drawn vehicles are queued to turn right, meanwhile all other traffic continues zooming by heading straight. Some vehicles are moving slow on segment 2 (queued to turn right) while others move fast (going straight ahead) - Waze interprets this as traffic flow is moving fast. A junction box is needed here to tell Waze that the traffic in segment 1 and 2 are related to segment 3. Waze now treats all the segments within it as a single intersection.

In this particular example, before the junction box was added, Waze always preferred this route during peak hour. After the junction box was added, Waze now sends drivers on a faster route because it knows the traffic is slow here when turning.

Junction boxes help Waze to understand the relationship between segments by treating them as a single intersection.

Improve data collected on intricate/complex intersections

Similar to the queuing example above, Waze has no understanding that traffic queuing across multiple segments might be related unless we tell it with a junction box. A junction box over this major intersection tells Waze to treat this as one intersection instead of looking at the individual segments within it.

In the below example, following the path of the green arrow, the driver needs to cross and potentially queue across five segments (which are all allowed and legitimate). The time the driver spends on each segment is irrelevant, whereas the time to traverse the entire intersection is what Waze needs to calculate times for the best route. Also note traffic queues in six different places, and with a single junction box, the route calculation is quickly optimised for all of those paths.

It may not be obvious an intersection is complex until you examine it carefully. This junction box helped Waze understand this is one giant intersection and that the total time to travel through it is what matters, not individual segments.
An example of a complex intersection that would benefit from a junction box. How long it takes a driver to transition each individual segment inside this complex intersection isn't very useful. It is much more useful for Waze to see this as "one intersection" by adding a junction box, and understand the transitions times for specific routes through it.

Where slip/turn lanes are permitted and used correctly, and on important roads, treat them as complex intersections. This helps Waze understand that all the segments are related and that queueing traffic could occur on multiple segments.

Important intersections with slip/turn lanes used correctly are considered complex intersections that will benefit from a junction box.

Fix roundabout routing issues and override voice prompts

Launched late 2021, junction boxes can now be applied to roundabouts. This allows editors to remove several map hacks and manage paths through the roundabout and override traffic instructions easily.

In the following example, drivers were given routing instructions to follow the red path despite there being a slip/turn lane to bypass the roundabout, resulting in frequent complaints. If the turn on the roundabout was turned off at the D exit, traffic coming from A, B, and D would be unable to exit the roundabout at D. This is wrong and should never be attempted.

This is poor practice and breaks entry from all points on the roundabout.

Once a junction box is applied to the roundabout, the path travelling from C to D can been turned off, subsequently forcing C to D traffic to the slip/turn lane. Because only the path between C and D was turned off, traffic from A, B and D can still exit at D.

Junction boxes on roundabouts are new in 2021, and allow turn control on paths and voice prompt overrides.

In the roundabouts page, section understanding navigation instructions, describes how Waze automatically determines how it announces “turn left/right/continue/u-turn” or “take the first/second/third/nth exit”. Because roundabouts are sometimes different shapes or connect at different points, Waze can get the direction wrong. Using a junction box, the Voice prompt can override the default instruction, improving the Waze app experience.