Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
1- Muslim scholars views that as long as women are in a safe company and the path is safe, it would be allowed from them to travel without mahram.
2- However, if there is a long distance between major cities where there is a significant isolated area, women should travel with a mahram for their safety and protection.
Answering your question, Sheikh Mustafa Umar, President of California Islamic University, states:
The Prophet said, “A woman should not travel except with a mahram [unmarriageable close-relative], and no man should visit her except in the presence of a mahram.” (Al-Bukhari)
This applies to traveling long distances [where one is allowed to shorten their prayers] and does not apply to living at home alone or wandering around one’s own city for everyday reasons.
The reason for the prohibition of travel without mahram is for the protection of women, and not because of some defect in them, as some people may ignorantly read into the text.
The Prophet’s statement was made in an environment where people would travel through deserts and encounter areas of isolation where virtually no one lived.
Throughout history, a number of Muslim scholars made exceptions to this rule, stating that as long as a women were in a safe company with other women present and the path was safe, it would be allowed.
Since most people travel via airplanes or trains, going direct from one city to another, there is no period of crossing through an isolated place, since there are always men and women inside the train/plane with them.
This would fulfill the condition of other women being constantly present and the path being safe.
However, if traveling by car through a long distance between major cities where there is a significant isolated area, the command of the Prophet would apply in order to protect women from passing through those areas. A car may break down on the road or some other incident could happen.
Almighty Allah knows best.