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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 2.0m/s ⇒ pass judge(using next slide formula)
    • lower than 2.0m/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)

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
enable_pass_judge bool [-] whether to use pass judge

Flowchart#

uml diagram

Known Limits#
  • tbd.