First, the facts. later, the personal observation ("The good stuff").
This interesting device is similar to a
revolving door or
turnstile in some of its structure, but has a very different function.
It has a
central vertical axle, with vertical
rows of
horizontal bars on it. It can be passed by pushing on the bars and
rotating them ahead of you on the axle, like a
revolving door. It has walls on two sides, so it can only be passed through along one line. Along one of the walls, it has a vertical row of bars, similar to the rows on the axle, but
staggered vertically by the space one bar takes up, so the rows on the axle can pass it.
Assuming that the gate can only rotate in one direction, then a person can only pass through it in one direction, because if they try to go in the wrong direction, they will be trapped between one of the rotating gates and the
stationary row of bars.
I've seen them used instead of turnstiles in many public facilities, such as
New York City subway stations, and at the entrances/exits of the
Bronx Zoo.
Here's a front-view diagram:
The gate rotates towards you on the left and away from you on the right.
___________________________
| | | |
|========) |R| |
| |O| |
| (========|T|========) |
| |A| |
|========) |T| Walk |
| |I| into |
| (========|N|========) |
| |G| this |
|========) | | side. |
| |C| |
| (========|O|========) |
| |L| |
|========) |U| |
| |M| |
| (========|N|========) |
| | | |
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Now, the anecdote. Ever since I was little (probably since I was
five or
six and first saw a revolving gate at the
Bronx Zoo) It's always seemed to me that these things were designed with the intent that anyone trying to go through the wrong side of the gate would, because of the stream of people traveling through the other side, be pressed into
jam.
(That last line used to end "...pressed into a jam-like substance." I had originally intended to write "pressed into jam." because it has a nice ring to it, and I don't know why I originally wrote something stupid-sounding instead. I like to say "Pressed into jam." referring to people.)