Is a woman allowed to ride a private car alone?

Question:

Is a woman allowed to ride a private car alone -without a Mahram (unmarriageable person), if the driver was an acquaintance of her family?

Answer:

1. What applies on the home applies on the private car, because both need a permission to enter (ride).

2. Therefore no one is allowed to be in it with the woman, other than her Mahram or husband, similar to the home.

3. Nothing is