Why is it ok to travel on shabbat elevator but not on an electric bus or train that stops on every station and no money is required just like an elevator ride ?
Every issue of the use of electricity , automation and the use of non-Jews on Shabbat requires serious consideration with each case studied individually. Many issues which have been ruled as permitted by some Rabbis are still considered forbidden by others. There are issues of Amirah le'Akum, Marit Ayin, increased weight resulting in the additional fuel consumption or more electric power, and Uvdin de' Chol. The example of the use of "Shabbat" elevator is not ok according to all.It was not allowed by all Rabbis. Rav Weiss zt"l forbade the usue of an elevator on Shabbat.(Minchat Yitzchok 3:60) .His reasoning is that the increase of passengers would require an additional usage of current and fuel and should be forbidden on Shabbat. This logic would apply equally to an electric bus. Also Rav Levi Halpern Director of the Institute for Science and Halacha, does not allow the use of a Shabbat elevator.. Although, it is permitted in Shmirat Shabbat Kehilchata (Shmirat Shabbat Kehalacha Vol. 1-23:49). However, the heter given there does not automatically apply for the use of an electric tram. Regarding the use of a bus, if we were to assume that all the electric issues were solved, there is still an issue of going out of Techum Shabbat which is the distance of approximately one kilometer out of city limits. (without going into all the Halachic details of Techum Shabbat and what constitutes city limits.) On the other hand though, I found a Teshuva of Rav Bentzion Chai Uziel in Piskei Uziel (siman 13). He was asked regarding if a Jew would be allowed on Shabbat to travel on an electrically or steam operated street car driven by a non- Jew. He allowed it with the following restrictions. It must be in an area where most of the residents are non- Jews. Otherwise, it is considered that the driving is for the Jew. If it goes through a Jewish area, however, it is forbidden to do so. He further stipulated that it be driven within city limits and the Jewish passenger would not have to use money. Also, the issue was discussed in Mareh Habazak (Vol. 3 answers 37 &38). But as in all these matters, the decision is in the hands of Gedolei yisrael who weigh and consider all the issues at hand and then decide for further generations in order to insure the preservation of the continued sanctity of Shabbat. We have seen over the years how many poskim were anxious of the ramifications of certain Heterim. In regard to the use of the Shabbat clock for the sake of cooking. In Shut Even Yekara of Rav Binyomin Aryeh Hacohen Weisszt"l (Av Bet Din of Tzernowitz)Part III, siman 85, he writes that he will not take part in a heter of using a Shabbat clock for cooking on Shabbat. This was reiterated in Shut Chelkat Ya'akov Part I. siman 57.Also in Yalkut Yosef on Shabbat siman 253. So there is much to learn and consider before the applying the heter for one thing to another. Kol Tuv.