Rear Collision Checker

The rear_collision_checker is a plugin module of the autoware_planning_validator node. It validates the planned trajectory by verifying that it does not lead to a collision with other road users (primarily vehicles, but also pedestrian/cyclists/motorcycles) approaching from lateral/rear directions. In particular, it is designed to detect potential rear-end collisions and entrapment risks when the ego vehicle is making a right/left turn or merging into an adjacent lane.

Inner Workings

The module operates by:

1. Identifying conflict lanes
   • Uses the current route and lanelet topology to determine lanes that the ego vehicle’s trajectory may intersect with during right/left turns or lane changes.
   • Focuses on lanes where vehicles, bicycles, or motorcycles could approach from behind or from a lateral direction, posing a potential rear-end or entrapment risk.
   • Considers the turn_direction of the approaching lanelets to filter out irrelevant lanes.
2. Filtering perception data
   • Subscribes to obstacle pointcloud and first filters by the conflict region, keeping only points that fall within relevant spatial bounds.
   • Performs clustering on the filtered points to form obstacle candidates.
   • Associates clusters with nearby lanelets and computes the nearest face of each obstacle along the lane direction.
   • Applies configurable range gates (forward/backward, lateral, height) and basic outlier rejection to discard distant or irrelevant clusters.
3. Estimating motion
   • For each selected object, determines its motion relative to the lane direction.
   • Estimates speed and direction based on frame-to-frame position changes along the lane’s centerline.
   • Maintains a per-lane tracking list to stabilize velocity estimation and reduce noise from perception flicker.
4. Calculating metrics
   • The calculation method and decision logic vary based on the selected collision assessment metric (e.g., Time-to-Collision). The module calculates the chosen metric and uses the result to determine if a collision risk exists.
5. Judging collision risk
   • Evaluates the selected metric results against predefined thresholds to determine whether a collision is likely.
   • Applies hysteresis logic:
     • on_time_buffer: Hazardous state must persist for this duration before marking the trajectory unsafe.
     • off_time_buffer: Safe state must persist for this duration before clearing the unsafe flag.
   • If check_on_unstoppable=false, the module will skip collision warnings in cases where the ego vehicle cannot realistically stop before the conflict area (to prevent unnecessary alerts when stopping is already infeasible).

Flowchart

WIP

General Parameters

Pointcloud Preprocess

Object Filtering

TTC

Ego Behavior

Collision Check For Blind Spot

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Changelog for package autoware_planning_validator_rear_collision_checker

0.53.0 (2026-09-29)

• Merge remote-tracking branch 'origin/main' into prepare-0.53.0-changelog

• feat(planning_validator): apply [agnocast_wrapper::Node]{.title-ref} to [planning_validator]{.title-ref} (#12964)

  • apply agnocast_wrapper::node
  • style(pre-commit): autofix

  * fix(autoware_planning_validator): feed stop checker per odometry message Restore the original VehicleStopChecker behavior: subscribe to /localization/kinematic_state and call addTwist() on every odometry message, instead of feeding the latest polled odometry once per trajectory cycle.

  • refactor(autoware_planning_validator): drop odometry subscriber comment
  • refactor(planning_validator): migrate to polling:: API
  • fix(planning_validator): adopt PlanningFactorInterfaceT<Node>
  • fix(autoware_planning_validator): launch as a standalone node and fix the agnocast build wiring
  • fix(autoware_planning_validator): pass the underlying rclcpp node to the planning test manager
  • style(pre-commit): autofix

  * refactor(autoware_planning_validator): declare the utils packages it includes and drop the stale comment ---------Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com> Co-authored-by: kobayu858 <<yutaro.kobayashi.2@tier4.jp>>

• chore(planning): update package maintainers (#13186)

• chore(pre-commit): update clang-format to v22.1.5 (#13126)

  • chore(pre-commit): update clang-format to v22.1.5

  * style(pre-commit): autofix ---------

• fix(planning_validator, control_validator): fix include path for angles header (#13026)

  • fix include path for angles header

  * add missing package dependency ---------

• Contributors: Koichi Imai, Mete Fatih Cırıt, Ryohsuke Mitsudome, Satoshi OTA, mkquda

0.52.0 (2026-06-30)

0.51.0 (2026-05-01)

• Merge remote-tracking branch 'origin/main' into tmp/bot/bump_version_base

• fix: bound int 32 range for rqt_reconfigure older than 1.1.4 (#12349)

• feat(lanelet2_extension): replace ported lanelet2_extension utilities functions (final) (#12173) Co-authored-by: Mamoru Sobue <<hilo.soblin@gmail.com>>

• feat(autoware_lanelet2_extension): replace remaining lanelet2_extension utilities functions - planning component (#12083)

  • replace getArcCoordinates in planning component
  • replace getCenterlineWithOffset in planning component
  • replace getRight/LeftBoundWithOffset in planning component
  • replace getExpandedLanelet(s) in planning component
  • replace combineLaneletsShape in planning component
  • remove log for empty combine_lanelet_opt

  * bind reference to optional value ---------Co-authored-by: Mamoru Sobue <<hilo.soblin@gmail.com>>

• Contributors: Sarun MUKDAPITAK, Yuxuan Liu, github-actions

0.50.0 (2026-02-14)

• Merge remote-tracking branch 'origin/main' into humble
• fix(planning_validator_rear_collision_checker): use autoware_utils_geometry type (#11940)
• docs(rear_collision_checker): revise sentence from README. (#11837)
• Contributors: Mete Fatih Cırıt, Ryohsuke Mitsudome, Zulfaqar Azmi

0.49.0 (2025-12-30)

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