We will be taking a long trip by car that will be spread out over three days with a break for Shabbat in the middle. What is the halacha for saying Tefilat HaDerech (Prayer for the traveler)? is it said just once for the entire journey? Or do we say it the beginning of each days journey?
While what Shalom writes is the generally accepted view, there is in fact a halachic opinion (Pri Chadash 110:5) that Tefillas Haderech should be recited only once, at the beginning of the trip.
As a compromise, R' Shneur Zalman of Liadi states (in his Siddur) that it should indeed be recited on all days of the trip - including, he says, days when you're not traveling but are still away from home (e.g., when staying at a hotel); however, from the second day of the trip onward, the names of G-d should be omitted at the beginning and end of the blessing (i.e., start out "...יְהִי רָצוֹן מִלְּפָנֶיךָ שֶׁתּוֹלִיכֵנוּ", and end with "בָּרוּךְ אַתָּה שׁוֹמֵעַ תְּפִלָּה"). In this way there is no concern about reciting a possibly unnecessary blessing.
Whether to say it on Shabbos is a different question. Rabbi L.Y. Raskin, dayan of the Chabad community of Stamford Hill, comments (in his notes to R.S.Z.'s Siddur) that most likely it would be like other petitionary prayers, which are not recited on Shabbos.
At the beginning of each day's journey that you're travelling. Any mitzva that gets stretched out over multiple days gets a new bracha each morning (e.g. involvement in Torah study, which is a continuous obligation).
It should be said when you leave a city (or a place where you've spent the night) when you're leaving to travel through uninhabited areas for at least 72 minutes. It should be said a maximum of once per day.
In Hayom Yom for the 19th of Tammuz, the following custom of the Rebbe Rashab (5th Lubavitcher Rebbe) is recorded:
A practice of my father's: When travelling, even when spending months in one place, he would recite t'filat haderech, the prayer for travellers (p. 86) daily after davening, omitting G-d's name in the conclusion.
In Eliezer Wenger's book, The Travelling Companion, he brings sources that explain that:
- any day of travelling requires Tefillat HaDerech
- It appears from many poskim that Tefilas Haderech does not need to be said during non-traveling days, i.e. when one is staying in one place for vacation, business, etc.
- with some exceptions, consecutive days of travel require Tefillat HaDerech every day.
See there for more details and sources