diff --git a/src/ground_vehicle.hpp b/src/ground_vehicle.hpp
--- a/src/ground_vehicle.hpp
+++ b/src/ground_vehicle.hpp
@@ -377,6 +377,41 @@ struct GroundVehicle : public Specialize
 			this->gcache.last_speed = this->cur_speed;
 		}
 	}
+
+protected:
+	/**
+	 * Update the speed of the vehicle.
+	 *
+	 * It updates the cur_speed and subspeed variables depending on the state
+	 * of the vehicle; in this case the current acceleration, minimum and
+	 * maximum speeds of the vehicle. It returns the distance that that the
+	 * vehicle can drive this tick. #Vehicle::GetAdvanceDistance() determines
+	 * the distance to drive before moving a step on the map.
+	 * @param accel     The acceleration we would like to give this vehicle.
+	 * @param min_speed The minimum speed here, in vehicle specific units.
+	 * @param max_speed The maximum speed here, in vehicle specific units.
+	 * @return Distance to drive.
+	 */
+	FORCEINLINE uint DoUpdateSpeed(uint accel, int min_speed, int max_speed)
+	{
+		uint spd = this->subspeed + accel;
+		this->subspeed = (byte)spd;
+
+		/* When we are going faster than the maximum speed, reduce the speed
+		 * somewhat gradually. But never lower than the maximum speed. */
+		int tempmax = max_speed;
+		if (this->cur_speed > max_speed) {
+			tempmax = max(this->cur_speed - (this->cur_speed / 10) - 1, max_speed);
+		}
+
+		this->cur_speed = spd = Clamp(this->cur_speed + ((int)spd >> 8), min_speed, tempmax);
+
+		int scaled_spd = this->GetAdvanceSpeed(spd);
+
+		scaled_spd += this->progress;
+		this->progress = 0; // set later in *Handler or *Controller
+		return scaled_spd;
+	}
 };
 
 #endif /* GROUND_VEHICLE_HPP */
diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -2630,38 +2630,14 @@ void Train::MarkDirty()
  */
 int Train::UpdateSpeed()
 {
-	uint accel;
-	uint16 max_speed;
-
 	switch (_settings_game.vehicle.train_acceleration_model) {
 		default: NOT_REACHED();
 		case AM_ORIGINAL:
-			max_speed = this->gcache.cached_max_track_speed;
-			accel = this->acceleration * (this->GetAccelerationStatus() == AS_BRAKE ? -4 : 2);
-			break;
+			return this->DoUpdateSpeed(this->acceleration * (this->GetAccelerationStatus() == AS_BRAKE ? -4 : 2), 0, this->gcache.cached_max_track_speed);
+
 		case AM_REALISTIC:
-			max_speed = this->GetCurrentMaxSpeed();
-			accel = this->GetAcceleration();
-			break;
+			return this->DoUpdateSpeed(this->GetAcceleration(), this->GetAccelerationStatus() == AS_BRAKE ? 0 : 2, this->GetCurrentMaxSpeed());
 	}
-
-	uint spd = this->subspeed + accel;
-	this->subspeed = (byte)spd;
-	{
-		int tempmax = max_speed;
-		if (this->cur_speed > max_speed) {
-			tempmax = max(this->cur_speed - (this->cur_speed / 10) - 1, tempmax);
-		}
-		/* Force a minimum speed of 1 km/h when realistic acceleration is on and the train is not braking. */
-		int min_speed = (_settings_game.vehicle.train_acceleration_model == AM_ORIGINAL || this->GetAccelerationStatus() == AS_BRAKE) ? 0 : 2;
-		this->cur_speed = spd = Clamp(this->cur_speed + ((int)spd >> 8), min_speed, tempmax);
-	}
-
-	int scaled_spd = this->GetAdvanceSpeed(spd);
-
-	scaled_spd += this->progress;
-	this->progress = 0; // set later in TrainLocoHandler or TrainController
-	return scaled_spd;
 }
 
 /**