Riding the Subway on Shabbat
Under the following conditions:
- One is not required to pay for public transport
- The transport is operating (stopping, starting, driving) for the purpose of non-Jewish passengers as well
Is it permissible to use such public transport?
For instance, it is commonly told that observant Jews in Boston used to use the (formerly) free outbound green line on Shabbat, but the practice was later abandoned. I have never seen any formally written evidence of this practice and whether it was officially sanctioned.
(An extension of a previous question: Is it prohibited to ride public transport that also operates on Shabbat)