Is it permissible to uncover the eyes or the entire face in the car at night?

A woman is permitted to uncover her face completely in an empty place where no non-mahram men can see her, such as a dark car. This is because the obligation to cover the face applies only in the presence of non-mahram men. This is supported by the hadith of Fatimah bint Qais (may Allah be pleased with her) in Sahih Muslim: "Spend your 'iddah in the house of Ibn Umm Maktum, for he is a blind man and you can put off your clothes there."