Q. Is one permitted for a man to sit next to a woman on a bus, train, or plane? Is it permitted to ask to have one's seat changed? If a woman does sit down next to him, is it more proper to get up and find another seat or is it more proper to stay put?
A. Horav Shlomo Miller’s Shlit’a opinion is that there are many variables and dynamic factors in any such situation and common sense and good judgment is imperative and must be kept. One must maintain the balance between maintaining proper tzenius and morality, while avoiding embarrassing people and creating a chilul Hashem.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a