Bidirectional Traffic

This module enables trajectory planning for vehicles on “single-lane bidirectional traffic” roads in autonomous driving systems. Here, “single-lane bidirectional traffic” refers to roads without a centerline, such as those commonly found in residential areas, as shown in the image below．

In the following descriptions, the term bidirectional traffic refers specifically to such single-lane bidirectional roads as shown in the image above.

Purpose/Role

The main roles of this module are as follows:

• Generating a driving trajectory along the left (or right) side of the road center

  This module provides a function to generate a trajectory along the left (or right) side of the road center on bidirectional traffic lanes. In some countries, traffic laws require vehicles to drive on the left or right side of the road center on bidirectional roads. For example, in Japan, Article 18, Paragraph 1 of the Road Traffic Act requires that vehicles must keep to the left side of the road center. Because of these legal requirements, this module provides the function to generate a trajectory that follows the left (or right) side of the road center on bidirectional roads.

• Giving way to oncoming vehicles on bidirectional traffic roads

  This module provides the function for the ego vehicle to stop on the left side of the road and give way to oncoming vehicles in all situations where vehicles must pass each other on bidirectional roads. Bidirectional traffic roads are often narrow, and it is dangerous for both the ego vehicle and the oncoming vehicle to pass while moving simultaneously. To avoid such dangerous situations, this module enables the ego vehicle to stop on the left side of the road until the oncoming vehicle has completely passed.

The representation of bidirectional traffic on a Lanelet map

Bidirectional lanelets are represented on a Lanelet map as two lanes with opposite directions that share the same LineString as their boundary. There is no need to assign any special tags to the lanelets.

Limitations

This module does not support the following situations or functionalities.

• Handling situations where passing is not possible

  Depending on factors such as lane width, the size of the ego vehicle and the oncoming vehicle, and the surrounding environment, simple behaviors like those shown in the video above may not be sufficient for passing. In such cases, special behaviours such as reversing or clearing an intersection may be required. However, this module does not provide such functionality.

• When the oncoming vehicle is giving way or moving slowly

  In cases where the oncoming vehicle is trying to give way or is traveling at a low speed, it may be more appropriate for the ego vehicle to continue driving rather than stopping to give way. However, this module does not make any decision about whether to give way to the oncoming vehicle – it always pulls over to the left and stops.

• Does not support the functionality of pulling into the shoulder to stop and give way

  Depending on the road width, the ego vehicle may need to enter the shoulder in order to give way to an oncoming vehicle. However, this module does not support such functionality.

Inner workings/Algorithms

This module does not support the following situations or functionalities.

Keep Left

This module detects bidirectional lanelets from the lanelet map and performs a keep left maneuver. When keeping left, the shift starts from the beginning of the lanelet immediately before the bidirectional lanelet, and ends at the end of the bidirectional lanelet.

Give Way

State transition of GiveWay

To perform the give way maneuver, the GiveWay module has five internal states.

• NoNeedToGiveWay

  No oncoming vehicles present and driving normally or oncoming vehicles are far away.

  

• ApproachingToShift

  If an oncoming vehicle is detected, it generates a path to shift left and pull over, approaching the shift start point.

  

• ShiftingRoadside

  

• WaitingForOncomingCarsToPass

  The ego vehicle stops and waits until all oncoming vehicles have passed.

  

• BackToNormalLane

  After the oncoming vehicle has passed, the ego vehicle performs a shift to return to its original driving lane.

  

The state transition diagram of the GiveWay module is shown below.

```plantuml @startuml skinparam state { BackgroundColor White BorderColor Black FontName “Arial” }

[*] –> NoNeedToGiveWay

state NoNeedToGiveWay : No oncoming vehicles,\ndriving normally state ApproachingToShift : Oncoming vehicle detected,\napproaching shift start

File truncated at 100 lines see the full file

Changelog for package autoware_behavior_path_bidirectional_traffic_module

0.46.0 (2025-06-20)

• Merge remote-tracking branch 'upstream/main' into tmp/TaikiYamada/bump_version_base

• feat(autoware_behavior_path_bidirectional_traffic_module): add a functionality for bidirectional traffic (#10394)

  • add bidirectional traffic module
  • first version
  • add virtual wall
  • WIP
  • apply new message type
  • revert autoware_trajectory change
  • WIP
  • developping...
  • fix bug
  • update module
  • remove stopping in BackToNormalLane mode
  • fix bug maybe
  • tidy
  • add document
  • rename images
  • add test, tidy.
  • catch up with latest branch
  • fix
  • style(pre-commit): autofix
  • update
  • downsizing svg files
  • fix
  • fix
  • tidy

  * fix

  Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

• Contributors: TaikiYamada4, Yukinari Hisaki