diff --git a/planning/behavior_path_planner/include/behavior_path_planner/utils/utils.hpp b/planning/behavior_path_planner/include/behavior_path_planner/utils/utils.hpp
index 50165f42af77d..14b2ea45d6285 100644
--- a/planning/behavior_path_planner/include/behavior_path_planner/utils/utils.hpp
+++ b/planning/behavior_path_planner/include/behavior_path_planner/utils/utils.hpp
@@ -409,6 +409,9 @@ void makeBoundLongitudinallyMonotonic(PathWithLaneId & path, const bool is_bound
 std::optional<lanelet::Polygon3d> getPolygonByPoint(
   const std::shared_ptr<RouteHandler> & route_handler, const lanelet::ConstPoint3d & point,
   const std::string & polygon_name);
+
+lanelet::ConstLanelets combineLanelets(
+  const lanelet::ConstLanelets & base_lanes, const lanelet::ConstLanelets & added_lanes);
 }  // namespace behavior_path_planner::utils
 
 #endif  // BEHAVIOR_PATH_PLANNER__UTILS__UTILS_HPP_
diff --git a/planning/behavior_path_planner/src/utils/utils.cpp b/planning/behavior_path_planner/src/utils/utils.cpp
index 06638cf2487fc..b1975147f2f24 100644
--- a/planning/behavior_path_planner/src/utils/utils.cpp
+++ b/planning/behavior_path_planner/src/utils/utils.cpp
@@ -3033,4 +3033,21 @@ void extractObstaclesFromDrivableArea(
     bound = drivable_area_processing::updateBoundary(bound, unique_polygons);
   }
 }
+
+lanelet::ConstLanelets combineLanelets(
+  const lanelet::ConstLanelets & base_lanes, const lanelet::ConstLanelets & added_lanes)
+{
+  lanelet::ConstLanelets combined_lanes = base_lanes;
+  for (const auto & added_lane : added_lanes) {
+    const auto it = std::find_if(
+      combined_lanes.begin(), combined_lanes.end(),
+      [&added_lane](const lanelet::ConstLanelet & lane) { return lane.id() == added_lane.id(); });
+    if (it == combined_lanes.end()) {
+      combined_lanes.push_back(added_lane);
+    }
+  }
+
+  return combined_lanes;
+}
+
 }  // namespace behavior_path_planner::utils