diff --git a/simulator/simple_planning_simulator/src/simple_planning_simulator/simple_planning_simulator_core.cpp b/simulator/simple_planning_simulator/src/simple_planning_simulator/simple_planning_simulator_core.cpp
index 9599d24bfa2b9..3f92bbe8e92a1 100644
--- a/simulator/simple_planning_simulator/src/simple_planning_simulator/simple_planning_simulator_core.cpp
+++ b/simulator/simple_planning_simulator/src/simple_planning_simulator/simple_planning_simulator_core.cpp
@@ -321,9 +321,9 @@ void SimplePlanningSimulator::on_timer()
   }
 
   // calculate longitudinal acceleration by slope
-  const double ego_pitch_angle = calculate_ego_pitch();
-  const double acc_by_slope =
-    enable_road_slope_simulation_ ? -9.81 * std::sin(ego_pitch_angle) : 0.0;
+  constexpr double gravity_acceleration = -9.81;
+  const double ego_pitch_angle = enable_road_slope_simulation_ ? calculate_ego_pitch() : 0.0;
+  const double acc_by_slope = gravity_acceleration * std::sin(ego_pitch_angle);
 
   // update vehicle dynamics
   {