From u- + -safiri.
usafiri (u class, no plural)
I haven't ever heard it before - for "bon voyage"/"safe travels" You would wish somebody "Safari njema"
Usafiri (...) mzuri is used in sentences on transportation. "Usafiri wa umma hapa si mzuri sana, lakini kumiliki gari pia ni ghali mno, vinginevyo ningekuwa nimeshajipatia moja - Public transport here is not very good, but getting a car is very expensive. I would’ve got one"... (from https://mymemory.translated.net/en/Swahili/English/habari-yako-mzuri-sana)
I would like to know the same. Perhaps a native speaker can explain it better.
I can only share information from the web here, but I am still learning to read in Swahili so I am not sure if this is about transportation services:
Here is a text from a newspaper in Swahili (I am afraid I cannot read it well, just some words):
And this is just an example sentence from Glosbe:
Tumetumiaje hali ya amani na mfumo mzuri wa usafiri?
How have we made use of peaceful conditions and convenient transportation?