[Proposal] roundabout support

[zusizusi]

We would like to propose a new module for roundabouts.

Background

Currently, Autoware's planning module doesn't officially support roundabouts. It appears the intersection module is being adapted to manage them, but this approach has several limitations:

• Turn Signal Behavior
  • The existing turn signal module only supports simple left and right signals. This isn't sufficient for regulations in some countries, like France and the UK, where drivers often need to signal their intended exit direction upon entering a roundabout.
• Roundabout Entry Logic
  • Vehicles inside a roundabout generally have the right of way. Entering vehicles should slow down and ensure the path is clear before proceeding. While the current intersection module can simulate this with right_of_way and yield tags, it complicates map creation and seems to assume a full stop for unsignalized intersections.

Related old discussion: https://github.com/orgs/autowarefoundation/discussions/4020

Proposal Solutions

We propose adding roundabout support to Autoware, focusing on the following:

Base Map Specifications

The regulatory elements for a roundabout are defined. Roles such as entry, exit, and internal are added to manage each lanelet.

Turn Signal Logic

We'll enhance the turn_signal_decider to include roundabout-specific logic:

• Standard Options: In param.yaml, we'll allow three options for roundabout entry/exit signals: Right, Left, or None.

• Country-Specific Rules (UK/France): For regulations requiring exit signaling upon entry, we plan to link the exit lanelet ID and desired turn signal direction (e.g., exit_turn_signal_left, exit_turn_signal_right) to an optional tag on the entry lanelet. The ego vehicle's path will then determine and output the appropriate signal for the corresponding exit. This flexible approach accounts for ambiguous or varying country-specific regulations.

  • Example Optional Tag: <tag k="exit_turn_signal_left" v="301599"/> (where 301599 is an exit Lanelet ID)

• Timing for Initiating Exit Turn Signals

  • In some countries, ego vehicle is required to start indicating their exit with a turn signal as soon as they pass the exit prior to their desired one. To allow for flexible control over when the exit turn signal is activated, we will embed an optional tag {enable_exit_turn_signal: true} in the lanelet where the exit turn signal should begin.

• Example Video (Demonstrates signaling towards the exit when entering):

• Screencast.from.2025.07.22.16.17.49.webm

• related PR(Draft): feat(turn_signal_decider): add turn signal support for roundabouts autoware_universe#10944

New Roundabout Module (behavior_velocity_roundabout_module)

Add a new behavior_velocity_roundabout_module to the behavior_velocity_module. This module will set an attention area (within the roundabout), when entering a roundabout, and check for collisions with predicted objects similar to the intersection module.
We

The functions of this module are as follows:

• Define following stop lines
  • Default stop line
  • Attention stop line: This line is the collision point between the entry lanelet and the internal lanelet.
  • Overpass judge line: This line determines whether the ego vehicle can stop at the attention stop line.
• Collision check with other objects when entering
• Determines whether to proceed or stop based on the collision detection results:
  • If no collision objects are detected, the ego vehicle will not stop.
  • If collision objects are detected and the ego vehicle can stop at the default stop line, it will stop at that line.
  • If collision objects are detected and the ego vehicle can stop at the attention stop line, it will stop at that line.
  • If collision objects are detected, but the ego vehicle has already passed the overpass judge line, the ego vehicle will not stop.

example video (WIP):

Screencast.from.2025.07.22.18.41.09.webm

Future Work

As this proposal is the first step, the following features are not included but will be needed eventually:

• Deceleration: slow down when entering.
• Occlusion check
• Check the blind spot for bicycles, etc.
  • The current blind spot module does not work well with roundabouts.
• Appropriate entry lane handling when there are multiple lanes at the entry
  • This may need to be resolved with the behavior path planner.
• Lane changes within the roundabout (multiple lane support)

To AWF members

We've aimed for compliance with all relevant national regulations. Please let us know if you find any gaps.
Additionally, we welcome your comments regarding the specifications.
As we continue development, we'll soon be asking for your review support. We appreciate your forthcoming assistance.

edit history

• 2025-07-25
  • add detail of New Roundabout Module
• 2025-07-28
  • add timing for Initiating Exit Turn Signals
• 2025-09-18
  • modify the map specification

[sasakisasaki]

@zusizusi Thank you for working on adding the awesome feature! It seems you are already working on the following PR. I'll review and support 👍

• feat(turn_signal_decider): add turn signal support for roundabouts autoware_universe#10944

[zusizusi]

@takayuki5168 @soblin cc @yhisaki
Could you please check this proposal?

[sasakisasaki]

@xmfcx @mitsudome-r It would be helpful if we could discuss this matter in today's Software Working Group.

As stated in the description of this proposal, we need to implement the new feature while ensuring it complies with traffic regulations in each country. In today’s meeting, I’d like to discuss this not only with those familiar with local traffic regulations, but also to ask for support from those who can help with development and review.

[mitsudome-r]

@zusizusi
Have you considered defining a regulatory elements for roundabouts instead of adding tags to individual lanelets?
I'm thinking of something like the following:

  <relation id='1001' visible='true' version='1'>
    <member type='relation' ref='1' role='entry' /> <!-- points to entry lanelets -->
    <member type='relation' ref='2' role='entry' />
    <member type='relation' ref='3' role='internal' />
    <member type='relation' ref='4' role='exit' />
    <member type='relation' ref='5' role='exit' />
    <tag k='subtype' v='roundabout' />
    <tag k='type' v='regulatory_element' />
  </relation>

I thought it becomes difficult for the behavior planners to know which lanes belongs to which roundabout in a situation where there are consecutive roundabouts as in the following image that I found from the UK example link you provided if we just add tags to individual lanelets. Instead, we could use regulatory element to provide "grouping" information.

[zusizusi]

@mitsudome-r cc @yhisaki @sasakisasaki
Thank you for your suggestion. I hadn't considered using a regulatory_element.
I think using a regulatory_element will make it more convenient to retrieve all the lanelets of the roundabout in the future, so I will adopt this approach.
Here is an example of an roundabout regulatory element:

  <relation id="3020000" version='1'>
    <member type="relation" role="entry" ref="3015718"/>
    <member type="relation" role="entry" ref="3015772"/>
    <member type="relation" role="entry" ref="3015057"/>
    <member type="relation" role="entry" ref="3015022"/>
    <member type="relation" role="entry" ref="3015362"/>
    <member type="relation" role="entry" ref="3015311"/>
    <member type="relation" role="entry" ref="3016019"/>
    <member type="relation" role="entry" ref="3016054"/>
    <member type="relation" role="internal" ref="3014843"/>
    <member type="relation" role="internal" ref="3016146"/>
    <member type="relation" role="internal" ref="3014887"/>
    <member type="relation" role="internal" ref="3016160"/>
    <member type="relation" role="internal" ref="3014863"/>
    <member type="relation" role="internal" ref="3016174"/>
    <member type="relation" role="internal" ref="3014873"/>
    <member type="relation" role="internal" ref="3016132"/>
    <member type="relation" role="internal" ref="3014838"/>
    <member type="relation" role="internal" ref="3014823"/>
    <member type="relation" role="internal" ref="3016139"/>
    <member type="relation" role="internal" ref="3014882"/>
    <member type="relation" role="internal" ref="3016153"/>
    <member type="relation" role="internal" ref="3016167"/>
    <member type="relation" role="internal" ref="3014868"/>
    <member type="relation" role="internal" ref="3016118"/>
    <member type="relation" role="exit" ref="3015870"/>
    <member type="relation" role="exit" ref="3015915"/>
    <member type="relation" role="exit" ref="3015815"/>
    <member type="relation" role="exit" ref="3015733"/>
    <member type="relation" role="exit" ref="3015196"/>
    <member type="relation" role="exit" ref="3015161"/>
    <member type="relation" role="exit" ref="3015988"/>
    <member type="relation" role="exit" ref="3015961"/>
    <tag k="type" v="regulatory_element"/>
    <tag k="subtype" v="roundabout"/>
  </relation>

[zusizusi]

autowarefoundation/autoware_lanelet2_extension#75
I crated the PR of roundabout regulatory element.

[zusizusi]

I created two PRs and both of them are merged.

Turn signal PR
autowarefoundation/autoware_universe#11235

behavior_velocity_roundabout_module PR
autowarefoundation/autoware_universe#11142