Your cat may feel stressed at the idea of being in the car, in a closed carrier. Firstly, you can start by teaching it how to use its pet carrier. To get it used to the car, you can place it in its carrier in the vehicle without starting the car, progressively turn on the engine, and finally do trips of increasing lengths. Be careful not to precipitate things, it could make things worse, and you could create stress, fear, and even phobia. To facilitate habituation, a food supplement that attenuates reactions linked to stress and fear and helps learning processes can help to prepare your cat. A cover or towel on top of the pet carrier can also help limit stress and provide security.