"When is the metro train arriving?"
Translation:מתי מגיעה הרכבת התחתית?
According to Wikipedia these are two different types of trains - one is light rail and the other heavy rail -
PS, the Tel Aviv future mass transit system would also be light rail, not metro, as far as I know.
Do I understand correctly that הרכבת התחתית, literally the train underneath, refers only to a heavy rail train? And that by "metro" you mean heavy rail?
FWIW, in the USA we don't really distinguish between light and heavy rail, especially since many transit systems have elements of both. The terms "subway", "metro", and (insert the name of your local system here) are used interchangeably to mean the entire urban rail system. For instance, in Boston the Green Line uses light rail cars and runs above ground along streets for most of its length, and is an integral part of the "T". Los Angeles' Metro Rail system consists of four light rail lines and two heavy rail (aka rapid transit) lines. I would unhesitatingly refer to all of the vehicles in these networks as "subway trains" or "metro trains".