A woman must have a legal (Sharee`ah legislated) mahram (male chaperone) before she can embark upon a journey. Without a mahram a woman cannot even travel for Hajj and Umrah – and these are from the greatest acts of worship – so it goes without saying that a journey lesser than these two mighty acts of worship also not permitted except with a mahram. It does not matter whether the journey (of leaving her home village, town or city) is short or long; it matters not whether she has a group of women with her or she is alone; it matters not whether she is young, pretty and vulnerable or old, unattractive and experienced; it does not matter whether she leaves by car or plane or ship – regardless of these things, a woman is required to have a mahram upon her travels. This is due to the hadeeth of Ibn ‘Abbaas (radiyallaahu `anhumaa) who narrated from the Prophet (salallaahu `alaihi wassallam) that he said: “A woman is not allowed to be alone with a man unless there is with her a mahram. And a woman is not allowed to travel except along with a mahram.” A man stood up and said: “O Messenger of Allaah! My wife has left out to perform Hajj and I have enlisted for the army in battle.” So the Prophet (salallaahu `alahi wassallam) said: “Go and and perform Hajj along with your wife.” (Bukhaaree and Muslim) So the Prophet did not seek from him details of whether she were with her a group of other woman, or whether she was young and beautiful, or whether the trip was going to be safe. So the mahram is a means of protection and preservation of the woman from harm and corruption; and harassment from wicked people who have not no scruples, honour or respect for woman. It is the duty of the male chaperone to prevent the woman from coming to harm or from falling into that which is forbidden. Before is a mind map illustration of the permissible male chaperones (mahaarim) of a woman, as explained by the great scholar and jurist, Shaikh Muhammad Ibn Saalih Al-`Uthaimeen (rahimahullaah).
Here’s a PDF version:
A journey in the Arabic language: To exit from the dwellings/buildings of a township wherein one resides. In the Sharee`ah: It is any leaving out that requires preparation that is not required by the resident of a town. A traveller no doubt makes a particular type of preparation for his journey – and a resident of a town does not do that, and the first of that is the intent. (Shaikh Al-Albaanee, Silsilah al-Hudaa wan-Noor, tape 025)
There are rare circumstances where a woman is forced to travel due to a necessity beyond her control, and she not able to find a mahram. In this situation she must seek guidance from the Scholars of Sunnah and Salafiyyah.