According to popular fiqh, Muslim women cannot travel without mahram. But in today’s age, travel has become so convenient, safe and secure that I think it is lawful for women to travel without mahram. The Prophet once said in this regard:

"A time will soon come when a woman will travel from al-Hira to circumambulate the Kaaba without needing any protection" (Sahih Ibn Hibban, Hadith No. 6679). There is an addition in the narration of Al-Bukhari, "fearing none but Allah" (Sahih al-Bukhari, Hadith No. 3595).

It means that at the time of peace and convenience, the condition of the mahram is optional. Islam, however, does not permit the free mixing of men and women. For instance, in the view of Islam, it is not suitable for a man to share a room with a woman if they both are unrelated. Islam asks its followers to maintain a distance of respect, dignity and modesty with each other. This is a safeguard for the personal and private spaces of both genders.

Source: The Seeker’s Guide