sans contact embarqué

17:16 Apr 29, 2018 

That's not quite accurate, I'm afraid: 'sans contact' very specifically means 'contactless' — this is long-established and well-document standard terminology. It refers to the fact that there is not ELECTRICAL contact required — the nexst step on from the 'smartcards' containing a chip but requiring conductive contact.
'Touch free', however, is a newer and I think woollier concept — it is more descriptive, and does not make any specific statement about electrical contact — although of course the latter would be impossible without touch! Conversely, though, there are things like bathroom taps that if they were not touch free would not involve ELECTRICAL contact, just hand contact.

So as such, 'touch free' is if you like just one subset of all 'sans contact' possibilities

In my view, departing from the standard, accepted translation of a technical term on the basis of supposition as to what the actual situation MIGHT be amounts here to over-interpretation — extrapolating beyond "what is written" to "what we think they meant".

Whatever the wider context may be, it couldn't invalidate 'contactless'; it is possible, however, that it might invalidate 'touch free'.

17:00 Apr 29, 2018 

Tony, I don't know whether "touch free" and "contactless" are synonymous but if they're not, then I agree with your original point that a precise translation would require knowledge of the specific bus system. Without that, the issues are (1) whether the bus uses the "vaguely near" system and, if we can't know, then (2) whether contactless is more inclusive and therefore a safer choice than touch-free. On the first issue, I'm willing to guess yes because the buses in my town do use the "vaguely near" method, which to you implies "touch free," and because Googling images of "valideur sans contact" produces many pictures of "vaguely near" swipes. On the second, again, I don't know but will defer to you.