Is it permissible to travel on a bus, subway or trolley in Shabbat if payment is rendered before Shabbat such that no handling of money is involved?
Rav Shemuel Pinhasi (contemporary), in his work "Daber Davar" (1:21; listen to audio recording for precise citation), rules that traveling on public transportation on Shabbat is strictly forbidden under all circumstances. If one travels outside his city, then the trip is certainly forbidden due to the prohibition of "Tehum Shabbat" traveling a distance of two thousands cubits outside one's city. And even traveling within the city, Rav Pinhasi writes, entails several Shabbat prohibitions, including the prohibition of "Uvda De'hol" performing weekday activity. Furthermore, one's mere presence on a bus or train may constitute a Shabbat violation in that it increases the activity of the vehicle's engine. The Hatam Sofer (Rabbi Moshe Sofer, Hungary, 1762-1839) went so far as to classify those who travel by train on Shabbat under the category of "Mumar" (apostates). In any event, the consensus among all authorities is that one may not travel by public transportation on Shabbat, even for the purpose of a Misva such as attending the synagogue, and even if the conductor/driver and crew are all non-Jews. Rav Ovadia Yosef codifies this Halacha in his work Yehaveh Da'at (6:16).
Similarly, it is forbidden for a person to travel in an airplane during Shabbat, even if he boards before Shabbat and disembarks only after Shabbat. This often occurs on westbound flights from Los Angeles to the Far East that leave Los Angeles on Friday afternoon. The plane flies through time zones where it is currently Shabbat, and then lands in the Far East on Saturday night. Rav Pinhasi (Daber Davar 11:15) rules that it is forbidden to take such a flight even if the pilot and crew members are not Jewish, since one's mere presence on the airplane increases the engine's activity. Furthermore, it is all but impossible to avoid activating electricity while walking about the aircraft, not to mention that one will be unable to recite Kiddush and conduct a Shabbat meal as required by Halacha under such circumstances.
Summary: It is forbidden to travel on public transportation vehicles on Shabbat under any circumstance, even if one paid before Shabbat. It is likewise forbidden to fly in an airplane on Shabbat, even if one boards before Shabbat and disembarks after Shabbat.
