Woman travelling with the driver in one car, and her mahram in another car, travelling with her
Question

                There is a woman who wants to travel to Madinah in a car with the driver, and with her brother in another car; is that permissible?
Praise be to Allah.
    Firstly: 

    The basic 
    principle is that it is not permissible for a woman to travel without a 
    mahram, whether the journey is long or short, because of the report narrated 
    by al-Bukhaari (1729) and Muslim (2391) from Ibn ‘Abbaas (may Allah be 
    pleased with him) who said: The Prophet (blessings and peace of Allah be 
    upon him) said: “No woman should travel except with a mahram.” 

    See also the 
    answer to question no. 110929 

    Secondly: 

    It is not 
    permissible for a woman to travel with a driver who is not her mahram, if 
    there is no one else with them, whether that is on a journey or otherwise, 
    because this comes under the heading of khulwah (being alone with a member 
    of the opposite sex), which is haraam. In the hadeeth it says: “No man 
    should be alone with a woman without there being a mahram present.” Narrated 
    by al-Bukhaari (5233); Muslim (1341). 

    See also the 
    answer to question no. 10374 

    Thirdly: 

    If what the 
    questioner means is that there are other women with her in the car, in such 
    a way that there is no forbidden khulwah (i.e., they are adults, of sound 
    mind and so on), and that her mahram is also present during the journey, but 
    he is in another car because there is no room for her in the car in which 
    her brother is, or the group is spread out in such a manner that the men are 
    in one car and the women are in another car during the journey, then there 
    is nothing wrong with that, if the two cars are travelling together. 

    Shakh Ibn 
    ‘Uthaymeen (may Allah have mercy on him) said: 

    Undoubtedly if 
    a person travels with his mahram, such as his wife or a female relative, in 
    the same car, that is better and is more on the safe side. But if there is a 
    group of cars travelling together and making stops together, then there is 
    nothing wrong with putting the women in one car and the men in the other 
    car. But it is essential that the driver of the (women’s) car should not get 
    separated from the car in which the male mahrams are, so that the mahram can 
    keep an eye on the car in which his female mahram is.

    Fataawa 
    al-‘Uthaymeen, 
    21/216 

    But if what is 
    meant is that the woman will travel on her own in the car with the driver, 
    that is not permissible, because of what we have mentioned above about 
    forbidden khulwah.

    And Allah 
    knows best.