Q: Are women permitted to travel alone?
A: According to the authoritative view, based on various hadith, females ages 7 and up are not permitted, in general, to travel without a mahram. This prohibition includes travel for a voluntary hajj, visitation, business, and any other journey (as defined by custom and not by distance) requiring a mahram.
It has been narrated that a mahram is not required for distances less than that which permit shortening and combing prayer.
The Imams do make mention of a view which permits the above mentioned types of travel along with all other permissible travel so long as the way is safe.
Source: Kashshaf al-Qina’, al-Insaf, and al-Furu’