An inlet, positioned to access the flow of air passing around and under a moving vehicle, may draw in air which is conveyed through a duct and discharged to cool a brake on a vehicle. The inlet has a closure. The closure is opened and closed on demand by a temperature-operated actuator incorporating an active or smart material under the direction of a controller. In embodiments, a sensor, suitably positioned to sense a temperature representative of the brake temperature, communicates the sensed brake temperature to the controller. The controller may respond to the sensed brake temperature, by triggering operation of the actuator. Typically the closure is opened to allow passage of cooling air to the brake when the sensed brake temperature exceeds, or is anticipated to exceed, a predetermined temperature.