Traffic Light Stop

Purpose/Role

This module modifies DP trajectories if they are found to run through a red or amber traffic light. If it finds that the DP trajectories causes the ego to cross or overshoot a red/amber traffic light, it will insert a stop point to ensure traffic rules compliance.

This module uses the TrafficLightComplianceChecker to check for violations. For details of the compliance checker logic refer to Compliance Checker Documentation.

The TrafficLightComplianceChecker will check for violations and return the results. The traffic light stop module will then scan the provided results for any red/amber light crossing. If the trajectory is crossing a red/amber light then a stop point is inserted.

Algorithm Overview

The following diagram shows the overall logic flow of the TrafficLightStop module:

Interface

Context & Data

The module utilizes the following data from TrajectoryModifierContext & InputData:

• Vehicle Info: Used to account for the vehicle's dimensions (longitudinal offset) when checking for stop line intersections & computing stopping margin.
• Lanelet Map: Used to find regulatory elements (traffic lights) and their associated stop lines.
• Traffic Light Signals: Provides the current state (color) of traffic light groups.
• Route: Used to map traffic light signals to lanelets and filter those that are relevant to the vehicle's path.
• Odometry: Provides the current ego velocity to determine if ego is stopped and to calculate stopping distances.
• Acceleration: Provides the current ego acceleration to calculate stopping distances.

Parameters

The module parameters are grouped under traffic_light_stop section of trajectory_modifier.param.yaml

Parameter name	Type	Default	Description
stop_margin	double	0.75	[m] Distance to keep from stop line (measured from ego front)
stop_for_red_light	bool	true	Flag to enable/disable stopping for red light violation
stop_for_amber_light	bool	false	Flag to enable/disable stopping for amber light violation
treat_amber_light_as_red	bool	false	When true, amber lights are treated identically to red lights (rejection on intersection regardless of distance).
treat_unknown_light_as_red	bool	false	When true, unknown lights are treated identically to red lights (rejection on intersection).
overshoot_tolerance	double	0.0	[m] Maximum distance between the stop line and the trajectory stop point to consider the trajectory feasible.
th_stable_duration_red	double	0.2	[s] Minimum duration a RED light must be seen before it is considered active (only when ego is moving).
th_stable_duration_amber	double	0.2	[s] Minimum duration an AMBER light must be seen before it is considered active (only when ego is moving).
th_amber_rejection_hysteresis	double	0.5	[s] Duration to persist an amber rejection state to prevent "flipping" due to minor velocity/distance changes.
crossing_time_limit	double	2.75	[s] Maximum time allowed for the ego vehicle to cross the stop line after an amber light appears.