Konkrét példák (Amerika): https://www.star-k.org/articles/kashrus-kurrents/6949/a-halachic-guide-to-tefilas-haderech/
One should say it after one has hit the road. And one should not say it other than in the case that one has to go a parsah [approx. 4 km]; but [if] less than a parsah one should not end [the prayer] with "barukh...". And ab initio, one should say it within the first parsah (Rashi and the R"i) And one forgot to say it, one may say it the entire time one is on the road, as long as one did not yet reach within the parsah adjacent to the city in which one wants to lodge; and from that point on, one should say it without the blessing.
A feltétel még csak magjában sem látszik a Talmudban, de a Metivtá hoz egy sor risont, akinek látszólag mégiscsak pontosan ez a girszája (hechzik, 270. o., 6. lábjegyzet).
The Gemara discusses specific details pertaining to this prayer. When does one pray? Rabbi Ya’akov said that Rav Ḥisda said: From when one sets out on his journey, and not before. How long must one’s planned journey be in order to require him to recite this prayer (Ba’al Halakhot Gedolot)? Rabbi Ya’akov said that Rav Ḥisda said: At least a parasang. How does he recite this prayer? Rav Ḥisda said: Only while standing in one place. Rav Sheshet said: Even walking or sitting.
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When one desires to leave, he should say, "May it be Your will, God, my Lord, to allow me to depart from this metropolis in peace." If one departs in peace, he should say:
I thank You, God, my Lord, for allowing me to depart in peace. As You have allowed me to depart in peace, lead me [on my way] in peace, direct my steps in peace, support me in peace, and save me from the hands of the enemies and lurking foes on the way.