In the Name of Allaah, the Extremely Merciful, the Bestower of Mercy. . .
Shaykh Ibn al-`Uthaymeen (rahimahullaah) says:
It is not permissible for a man to be alone with a woman (by herself) in a vehicle, except and unless he is her mahram, because the Prophet ﷺ said:
No man should be alone with a woman without there being a Mahram present.(1)
However, if there are two women with him or more, then there is no objection. This is because there is no privacy or seclusion (available between the lady and the driver) in this case – with the condition that it is safe and not a journey. And Allaah is the Granter of Success.(2)
Umm Sufyaan Fatimah
(1) Muslim no. 1241
(2) Fataawa li-Shaykh Muhammad bin Saalih al-`Uthaymeen wa `Alayhi Tawqee`ah.