Handling Roundabout

[beyzanurkaya]

Limitations of the Current Intersection Module for Roundabouts
The current intersection module has certain limitations when it comes to roundabouts.

These limitations are as follows:

• Checking Obstacle: In the current intersection module, if the EGO is inside the roundabout, it is not checked by the behavior_velocity_planner for obstacles even though the intersection module is registered. Instead, only the obstacle_stop_planner checked the obstacles.

     

roundabout-obstacle.mp4

roundabout-obstacle2.mp4

Attention areas change after EGO entering the roundabout:

attention_area.mp4

Green areas are attention areas

• Wait/Drive: The right_of_way and yield tags for intersections allow EGO to consciously wait or continue to drive. For example, if EGO is on the main road and a vehicle is leaving an intersection, it should not wait for that vehicle. Or if EGO is leaving the intersection on the main road, it must consider the other vehicles on the main road and wait. We can achieve this with rigth_of_way and yield tags. But when it comes to the roundabout's annotation, it becomes complicated because of the roundabout's structural design. So when in and around the roundabout the EGO has no conscious wait/drive ability.

• Turn on Signal: In YTU map, the turn directions of the roundabout's lanes are straight. This causes the autonomous vehicle to not signal when entering, exiting, or passing through the roundabout.

  • According to the rules, when entering the roundabout, EGO must give a signal in the direction it will exit.
  • While making a U-turn, it must signal left when entering, while it must signal right when exiting the roundabout. For this, the lanes must be divided and the exits must be annotated separately in the current intersection module. At this point, the annotation of the roundabout and the adding the right_of_way and yield tags become complicated. On the other hand, If we annotated the roundabout as a single piece then we may turn on the wrong signal.

• Registration of the Intersection Module: The intersection module is registered when the lanes have a turn_direction tag. However, since roundabouts have a more complex structure, the presence of overlap lanes with a turn_direction tag is not enough for roundabouts.

Possible solutions:

• Registration: It makes more sense to create scene_roundabout file in behavior_velocity_intersection_module rather than creating a new module. The roundabout module will register if it has the lane <tag k="roundabout" v="yes"/>

Additionally, entrance and exit lanes can be added as optionalTags during annotation.

e.g.
- <tag k="roundabout_entry" v="yes"/>
- <tag k="roundabout_exit" v="yes"/>

• Checking Obstacle: Until the roundabout module is unregistered, the entire attention area must stay the same and predicted objects must be checked while inside the EGO roundabout.

• Features: EGO should follow when the roundabout module is registered should be defined in this module.

  • slow_down
  • select_enter_lane
  • check_crosswalk
  • yield_to_traffic
  • calculate_enter_space
  • decide_enter
  • signal_exit

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So what do you think of this? Do you have any ideas or suggestions?

[beyzanurkaya]

@soblin
our YTU campus map: map
roundabout scenarios: roundabout scenarios

[soblin]

@beyzanurkaya Thanks a lot, I just started working on this topic. According to Japan road traffic rules EGO does not need to turn signal when entering the roundabout but only need to turn signal when exiting the roundabout just before the exit. It seems that we need several different handlings depending on the region.

[soblin]

FYI

Tier4 is trying to create a lanelet2 map for this roundabout: https://earth.google.com/web/search/35.4980448,134.2263538/@35.49806264,134.22641101,7.765741a,202.42246793d,35y,15.39030326h,0t,0r/data=CigiJgokCUaEGoPe0EFAEWMGSnuszkFAGbcut0MeeWFAIeIOPT2KeGFAOgMKATA

I found a video of this roundabout
https://www.youtube.com/watch?v=yRYT2jfW5Ms

Common roundabout geometry

There is a center island and a inscribed circle around center island. There are several splitter islands to divide entry/exit lanes. Inside the inscribed circle there will be one/more lanes (like arc de triomphe https://www.youtube.com/watch?v=-2RCPpdmSVg)

[soblin]

@beyzanurkaya I agree with the idea to divide the roundabout lane at least "entry" part and "exit" part because

• Blinker maybe necessary at the entry in some countries. At least in Japan and in the US turn signal is not necessary on the entry
• Blinker is seems to be necessary across all the countries including Japan, US, Turkey. I'll look for if there are any exceptions.
• Priority differs at the entry/inside/exit of the roundabout. In Japan EGO needs to yield vehicles inside roundabout when entering, but after that it has priority over merging vehicles so it does not yield inside roundabout (otherwise the traffic flow would not be smooth)

For autoware-wise the lanelet representation is critical for predicting other vehicles inside/outside of roundabout. To distinguish the predicted paths of a vehicle inside roundabout which is going to exit the ring / keep running in the ring, the "roundabout area" part needs to diverge to the next "roundabout area" and the exit lane. Also I observed that the roundabout Tier4 is now working on has "splitter island"s and they give good hints how the "roundabout area" should be divided.

Here is a rough idea of how to divide the lanelets for our project.

Note that Japan is left-hand traffic and there is only one lane inside the circle.

First, the inner ring is divided into 6 pieces. This corresponds to the number of merging roads . The 4 splitter islands help to divide the inner ring. Also I added two division lines, though they are unnecessary if I come up with better solution.
Once the inner ring is divided I could easily connect the entry/exit lanes. In this process the splitter islands were very useful.

I think this map suffices to plan the route / predict the paths of entering/exiting vehicles.

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The blinker is handled in behavior_path_planner, so each lane needs to have "roundabout" tag to distinguish normal intersection and roundabout.

[soblin]

Actions items:

• How to divide the lanelets for routing/blinker/prediction
  • And how to annotate the "roundabout" tag ?
  • Do we handle roundabout with more than two lanes in it ?
• additional feature for prediction/blinker
• Which module should handle ?
  • I agree with adding scene_roundabout_module.cpp under the behavior_velocity_intersection_module.

[soblin]

For a roundabout with multiple lanes, we can divide the inner ring to multiple lanes for each division. Since there are same number of lanes at the entry and exit we can connect the entry/exit and the inner lanes as shown in this figure.

This division gives the following routes for instance.

According to this material lane change is prohibited inside roundabout. https://www.co.washington.mn.us/DocumentCenter/View/6395/Roundabout-U-Brochure-Oct2014?bidId= , which supports this style of representation.