diff --git a/planning/autoware_obstacle_stop_planner/src/adaptive_cruise_control.cpp b/planning/autoware_obstacle_stop_planner/src/adaptive_cruise_control.cpp
index ee2eadac6f780..82a4d5a7ec550 100644
--- a/planning/autoware_obstacle_stop_planner/src/adaptive_cruise_control.cpp
+++ b/planning/autoware_obstacle_stop_planner/src/adaptive_cruise_control.cpp
@@ -111,16 +111,6 @@ double getDistanceFromTwoPoint(
   }
 }
 
-constexpr double sign(const double value)
-{
-  if (value > 0) {
-    return 1.0;
-  } else if (value < 0) {
-    return -1.0;
-  } else {
-    return 0.0;
-  }
-}
 }  // namespace
 
 namespace autoware::motion_planning
@@ -573,7 +563,7 @@ double AdaptiveCruiseController::calcUpperVelocity(
 }
 
 double AdaptiveCruiseController::calcThreshDistToForwardObstacle(
-  const double current_vel, const double obj_vel)
+  const double current_vel, const double obj_vel) const
 {
   const double current_vel_min = std::max(1.0, std::fabs(current_vel));
   const double obj_vel_min = std::max(0.0, obj_vel);
@@ -590,7 +580,7 @@ double AdaptiveCruiseController::calcThreshDistToForwardObstacle(
 }
 
 double AdaptiveCruiseController::calcBaseDistToForwardObstacle(
-  const double current_vel, const double obj_vel)
+  const double current_vel, const double obj_vel) const
 {
   const double obj_vel_min = std::max(0.0, obj_vel);
   const double minimum_distance = param_.min_dist_standard;
diff --git a/planning/autoware_obstacle_stop_planner/src/adaptive_cruise_control.hpp b/planning/autoware_obstacle_stop_planner/src/adaptive_cruise_control.hpp
index 7535986f1db85..ce57f585197ad 100644
--- a/planning/autoware_obstacle_stop_planner/src/adaptive_cruise_control.hpp
+++ b/planning/autoware_obstacle_stop_planner/src/adaptive_cruise_control.hpp
@@ -203,8 +203,8 @@ class AdaptiveCruiseController
   double estimateRoughPointVelocity(double current_vel);
   bool isObstacleVelocityHigh(const double obj_vel);
   double calcUpperVelocity(const double dist_to_col, const double obj_vel, const double self_vel);
-  double calcThreshDistToForwardObstacle(const double current_vel, const double obj_vel);
-  double calcBaseDistToForwardObstacle(const double current_vel, const double obj_vel);
+  double calcThreshDistToForwardObstacle(const double current_vel, const double obj_vel) const;
+  double calcBaseDistToForwardObstacle(const double current_vel, const double obj_vel) const;
   double calcTargetVelocity_P(const double target_dist, const double current_dist) const;
   static double calcTargetVelocity_I(const double target_dist, const double current_dist);
   double calcTargetVelocity_D(const double target_dist, const double current_dist);
diff --git a/planning/autoware_obstacle_stop_planner/src/debug_marker.hpp b/planning/autoware_obstacle_stop_planner/src/debug_marker.hpp
index ac043dd895ea7..4400368cc3d70 100644
--- a/planning/autoware_obstacle_stop_planner/src/debug_marker.hpp
+++ b/planning/autoware_obstacle_stop_planner/src/debug_marker.hpp
@@ -77,7 +77,7 @@ class DebugValues
    * @brief get all the debug values as an std::array
    * @return array of all debug values
    */
-  std::array<double, static_cast<int>(TYPE::SIZE)> getValues() const { return values_; }
+  const std::array<double, static_cast<int>(TYPE::SIZE)> & getValues() const { return values_; }
   /**
    * @brief set the given type to the given value
    * @param [in] type TYPE of the value