my family is planning to take the new train from Jerusalem to the airport tomorrow. I heard there are serious halachic problems using it because of work done on Shabbos. any insight?

ב"ה Shalom If we take into consideration the classic laws of benefit of Chilul Shabbat, when someone does Chilul Shabbat intentionally it is always forbidden for the person who desecrated Shabbat to benefit from the desecration. However, for others it is permitted to benefit immediately after Shabbat. (שו"ע סימן שי"ח סעיף א) Perhaps, we can compare this issue to someone who wants to get on a bus after Shabbat is out, which started travelling before Shabbat was out . In this case, since all that involves Chilul Shabbat has already passed, and none of the actions which are considered Chilul Shabbat, created any change in the vehicle, using the bus is permitted. (according to many Poskim) (פסקי תשובות אורח חיים סימן שיח, אות י"ז). However, since this is not a technical question, but one that has to do with religious character of the State of Israel, I don't feel it is my place to answer this question but it is something to be addressed by the Chief Rabbis. I heard that in a public oral discourse, the Sephardi Chief Rabbi, Rav Yitzchak Yoseph Shlit"a, ruled that although to our dismay Chilul Shabbat was committed in order to prepare the train, nonetheless ,according to the Shulchan Aruch, using the train is permitted. (Not on Shabbat, of course). Although, he himself mentions that there are considerations made by which some feel that by refraining from using the train, it may be leverage to prevent further Shabbat desecration in the future, this does not alter the ruling of the Shulchan Aruch , of being able to use the train . All the best