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.

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

• 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

Flowchart

@startuml
title modifyPathVelocity
start

:calc stop point and insert index;

:find offset segment;

:calculate stop pose;

:calculate distance to stop line;

if (state is APPROACH) then (yes)
  :set stop velocity;
  if (distance to stop point is below singed dead line length(-2[m])) then (yes)
    :change state to GO_OUT;
    stop
  elseif (no stop signal) then (yes)
    :change previous state to PASS;
    stop
  elseif (not pass through) then (yes)
    :insert stop pose;
    :change previous state to STOP;
    stop
  else(no)
    stop
  endif
elseif(state is GO_OUT) then (yes)
  if (signed arc length to stop line is more than restart length(1[m])) then (yes)
    :change state to APPROACH;
  endif
  stop
else(no)
  stop
endif

@enduml

Known Limits

• tbd.