we don’t usually map the thickness of walls or doors, turn stiles are typically mapped on nodes.
While it is not forbidden to map full height turnstiles on ways, it is done only 14 times, compared to 2851 on nodes (and I would expect all of these barriers (or nearly) to be oneway).
https://wiki.openstreetmap.org/wiki/Tag:barrier%3Dfull-height_turnstile
In the case of a oneway entrance, the suggestion is to map something like a 4cm-long stretch of oneway? For such kind of restrictions the typical solution is restriction relations.
Imagine being one step on this bridge and asking your router for indications to somewhere which requires going back:
https://wiki.openstreetmap.org/wiki/File:One_way_for_pedestrians_on_Fye_Bridge_-geograph.org.uk-_6507482.jpg
Would you want to be taken over the bridge and make a detour, or would you make a step back?