Well, the question is in the title…
Thanks
I do a parking=entrance, or you can make the roads going into the carpark as one way.
In my opinion, It’s kind of hard to tag entrances, perhaps they all should be under entrance instead, entrace=subway, entrance=parking…
I like the one-way road solution.
The risk is that it may be considered as a one-way street by some driving assistance software (sorry, i don’t have the real name of these software on the top of my mind), in which case going through a parking may be considered as a shortcut… (which it may be, but an expensive shortcut…)
This will lead to my next question in another thread. (about “private roads”…)
Could add
- higway=gate on a node
- access=permissive to the carpark roads
as well, but might be a bit over the top 
But this is Q&A stuff, not development → moved
Ha, ha!.. 
I would like that:
Turn left into “times square parking garage”
Go down 12 floors
[…]
Go up 12 floors
Turn right at Norrmalmstorg.
I prefer to map cap parks as areas, and then I add one-way service roads for the entrance and exit, that link the road and the perimeter of the car park, thus leaving no through route.
I do sometimes mark out the main “roads” in big ground-level car parks, but if the entrance and exit are on different roads and you’re concerned about routing programs sending people through them, don’t add these, or add access = permissive/private or something.