It depends on a lot of things to be honest. There's the local area, the actual degree of crowding, the seats themselves, the BMI of the people on either side...
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I'm kind of brining this back up, but I'd like to give some ideas on the flaws of 3+2 seating based on my observations over the past week on busy class 320 trains on the North Clyde Line, Glasgow. Of course, as I've already said
3+2 airline seating simply doesn't work. It's very difficult for people to use the middle seat, because naturally people use the window then aisle seats, leaving the middle one unused (as you would do, to respect the personal space of others). The problem comes when someone wants to use the seat in the middle. It's very hard to get in to it, especially if the person on the outside doesn't move to facilitate maximum utilisation. Yesterday morning, I noted 50% capacity on a busy (definitely more passengers than seats) service within the airline section at the end of the carriage, with people struggling to board the train. (That whole part of the train had 71% seat usage, as not all the seats were in airline-style - better, but still rather poor).
This morning, there was overcrowding (didn't count, but undoubtedly over the 135% threshold) due to a short formed train followed by a train with the middle carriage locked out of use. So it was pretty bad. Again, this morning, I noted 69% of seats (18 out of 26) used in my section of the carriage, with people choosing to stand rather than ask to use the middle seat (one person eventually plucked up the courage, but it took them a while).
Based on these figures, and assuming full use of 2+2 seating (which is very likely), a 2=2 arrangement would have been more successful than the 3+2 seating arranegement. Whilst there would have been more seats, uptake of the seats would have been greater, and therefore more people would have gotten a seat, so there would have been fewer standees and less of a "crush" in the vestibules.
So, it may work in some places, but I'm undeterred in my opposition to them in Glasgow.