(svn r20299) -Add: Make trains and road vehicles use a different area value to calculate air drag.

src/train.h

@@ -432,6 +432,15 @@ protected: // These functions should not be called outside acceleration code.
 		return GetVehicleProperty(this, PROP_TRAIN_TRACTIVE_EFFORT, RailVehInfo(this->engine_type)->tractive_effort);
 	}
 
+	/**
+	 * Gets the area used for calculating air drag.
+	 * @return Area of the engine.
+	 */
+	FORCEINLINE byte GetAirDragArea() const
+	{
+		return 120;
+	}
+
 	/**
 	 * Checks the current acceleration status of this vehicle.
 	 * @return Acceleration status.