<p>The device has vehicle roofs arranged between a fixed cross bar and a plane. The control unit has a marginal temperature sensor and a sensor for generating signals represented the standstill of a vehicle. The control unit is designed such that the filling of an air tube takes place only by standstill of vehicle and by falling of adjustable marginal temperature. The air tube is blown during existence of both requirements. An automatic ventilation of the air tube is passed during omission of requirements.</p>
