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Index

Traffic Light#

Role#

Judgement whether a vehicle can go into an intersection or not by traffic light status, and planning a velocity of the stop if necessary. This module is designed for rule-based velocity decision that is easy for developers to design its behavior. It generates proper velocity for traffic light scene.

brief

Limitations#

This module allows developers to design STOP/GO in traffic light module using specific rules. Due to the property of rule-based planning, the algorithm is greatly depends on object detection and perception accuracy considering traffic light. Also, this module only handles STOP/Go at traffic light scene, so rushing or quick decision according to traffic condition is future work.

Activation Timing#

This module is activated when there is traffic light in ego lane.

Algorithm#

  1. Obtains a traffic light mapped to the route and a stop line correspond to the traffic light from a map information.

    • If a corresponding traffic light signal have never been found, it treats as a signal to pass.
    • If a corresponding traffic light signal is found but timed out, it treats as a signal to stop.

  2. Uses the highest reliability one of the traffic light recognition result and if the color of that was not green or corresponding arrow signal, generates a stop point.

    • If an elapsed time to receive stop signal is less than stop_time_hysteresis, it treats as a signal to pass. This feature is to prevent chattering.

  3. When vehicle current velocity is

    • higher than yellow_light_stop_velocity m/s ⇒ pass judge(using next slide formula)
    • lower than yellow_light_stop_velocity m/s ⇒ stop

  4. When it to be judged that vehicle can’t stop before stop line, autoware chooses one of the following behaviors

    • "can pass through" stop line during yellow lamp => pass
    • "can’t pass through" stop line during yellow lamp => emergency stop

Dilemma Zone#

brief

  • yellow lamp line

    It’s called “yellow lamp line” which shows the distance traveled by the vehicle during yellow lamp.

  • dilemma zone

    It’s called “dilemma zone” which satisfies following conditions: - vehicle can’t pass through stop line during yellow lamp.(right side of the yellow lamp line)

    • vehicle can’t stop under deceleration and jerk limit.(left side of the pass judge curve)

      ⇒emergency stop(relax deceleration and jerk limitation in order to observe the traffic regulation)

  • optional zone

    It’s called “optional zone” which satisfies following conditions: - vehicle can pass through stop line during yellow lamp.(left side of the yellow lamp line)

    • vehicle can stop under deceleration and jerk limit.(right side of the pass judge curve)

      ⇒ stop(autoware selects the safety choice)

  • arrow-aware passing on yellow

    This feature enables smooth passing on a yellow signal in turn lanes to avoid sudden braking. Even in situations where the system would normally select STOP (Optional Zone) or EMERGENCY STOP (Dilemma Zone), it overrides the decision and selects PASS if all the following conditions are met: - The parameter enable_arrow_aware_yellow_passing is set to true. - The ego vehicle is in a turn lane (left or right). - The corresponding traffic light has a static arrow bulb defined in the map. - The signal state has transitioned from "Green" to "Yellow". (Note: If the transition is from "Red + Arrow" to "Yellow", the system decides to STOP for safety as per normal logic.)

Module Parameters#

Parameter Type Description
stop_margin double [m] margin before stop point
tl_state_timeout double [s] time out for detected traffic light result.
stop_time_hysteresis double [s] time threshold to decide stop planning for chattering prevention
yellow_lamp_period double [s] time for yellow lamp
yellow_light_stop_velocity double [m/s] velocity threshold for always stopping at a yellow light.
enable_pass_judge bool [-] whether to use pass judge
enable_arrow_aware_yellow_passing bool [-] whether to support arrow-aware passing on yellow
v2i.use_remaining_time bool [-] whether to use V2I remaining time information for traffic light decision
v2i.last_time_allowed_to_pass double [s] relative time against the time of turn to red - safety margin for passing through
v2i.velocity_threshold double [m/s] velocity threshold to change decision logic for V2I prediction
v2i.required_time_to_departure double [s] required time to departure for low speed scenarios to prevent unsafe passing

Flowchart#

uml diagram

Known Limits#
  • tbd.