Turnstiles for directing people in a single direction are a useful but klunky invention. I always approach them with great caution, especially when carrying a laptop bag over my shoulder.
It occurs to me that we could get the same effect with greater ease of use (and less tangled straps).
Picture the kind of hanging flaps used to keep cold in a walk-in refrigerator.
Now make them out of some kind of smart material.
When touched or pushed from one side, they become flexible, allowing people to pass through. Otherwise they would be set to be hard, preventing passage in the other direction.
The material could be transparent, or could have a no-entry sign imprinted on one side of it.
The material cost would likely be significantly lower than traditional turnstiles.