diff --git a/planning/behavior_path_lane_change_module/README.md b/planning/behavior_path_lane_change_module/README.md
index b26ec56cbb29e..b37e76e3c052e 100644
--- a/planning/behavior_path_lane_change_module/README.md
+++ b/planning/behavior_path_lane_change_module/README.md
@@ -298,6 +298,17 @@ First, we divide the target objects into obstacles in the target lane, obstacles
Furthermore, to change lanes behind a vehicle waiting at a traffic light, we skip the safety check for the stopping vehicles near the traffic light. The explanation for parked car detection is written in [documentation for avoidance module](../behavior_path_avoidance_module/README.md).
+The detection area for the target lane can be expanded beyond its original boundaries to enable detection of objects that are outside the target lane's limits.
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##### Collision check in prepare phase
The ego vehicle may need to secure ample inter-vehicle distance ahead of the target vehicle before attempting a lane change. The flag `enable_collision_check_at_prepare_phase` can be enabled to gain this behavior. The following image illustrates the differences between the `false` and `true` cases.
diff --git a/planning/behavior_path_lane_change_module/images/lane_change-lane_expansion-with.png b/planning/behavior_path_lane_change_module/images/lane_change-lane_expansion-with.png
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diff --git a/planning/behavior_path_lane_change_module/images/lane_change-lane_expansion-without.png b/planning/behavior_path_lane_change_module/images/lane_change-lane_expansion-without.png
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