We are beginning siman 2. Tefillas Haderech does not begin with baruch atah, like other brachos, but with yehi ratzon. Tosfos points out that tefillas haderech is primarily a tefilla and bakasha, rather than a bracha, so there is no need to begin with baruch atah. The bracha at the end is an outgrowth of praise and thanks to Hashem for listening to our tefillos.
The Maharam MiRottenberg would precede tefillas haderech to another bracha in order to begin tefillas haderech with a bracha. We have a halachic concept of bracha semucha lechaverta. When one recites multiple brachos in succession, the first bracha begins with baruch atah Hashem, and the subsequent brachos do not need to begin with Hashem’s name, because they follow the first bracha. Examples include birchos krias shema, where the bracha of yotzer ohr begins with baruch atah hashem, and ahavah rabba does not; or in birkas hamazon between the first bracha and subsequent brachos.
The opinion of Rabbeinu Tam is that the concept of bracha semucha lechaverta only applies to a bracha arucha, a bracha which begins and ends with baruch atah Hashem. A bracha ketzara, where the bracha does not end with baruch atah Hashem, cannot be used to precede tefillas haderech.
The Chayei Adam writes that one should precede tefillas haderech with a bracha achrona on food, in accordance with the opinion of the Maharam MiRottenberg. He chooses a bracha achrona following the opinion of Rabbeinu Tam that tefillas haderech must be preceded by a bracha arucha. Alternatively, a person could relieve themselves and use asher yotzar as their preceding bracha, but it must be a bracha arucha. The bracha rishona on food, in addition to the concern of Rabbeinu Tam, has another issue. The Mishnah Berurah raises the concern of a hefsek if one were to precede tefillas haderech with a bracha rishona, as a person would have to take a bite from the food or smell their item before reciting tefillas haderech.
Regarding the brachos used to precede tefillas haderech, if one recites birkas hamazon, they would recite tefillas haderech right after the bracha of al yechasreinu. If they are reciting al hamichya or borei nefashos, they recite tefillas haderech immediately following those brachos. Although borei nefashos appears to be a bracha ketzara, the poskim consider it a bracha arucha since its ending is similar to that of a bracha arucha.
Summary
One should precede tefillas haderech with a bracha arucha, such as any of the brachos achronos, or asher yotzar. If using birkas hamazon, tefillas haderech is recited immediately following the bracha of al yechasreinu.
