I’ve travelled extensively in trains that had lower and upper berths, and most commonly 3 levels. Bogies with 2 levels were limited to “First Class”.
The advantage of a lower berth is that, on a long distance journey, you can sit in your seat, walk around, look out the window, etc. The upper berth also had very little head-room, so you couldn’t really sit up, you had to lie down. Also, you couldn’t keep your legs dangling, because there were people right below you.
Let me try to help you visualize it:
3 berths:
o
Upper
------------------
Middle
------------------
[]Lower
------------------
= Window
o = fan at ceiling level
During the day, in a long-distance overnight journey, the middle berth folds into the wall, so you have:
o
Upper
------------------
[]Lower
------------------
The bench is long enough for 3 people to sit on, but anytime the persons who have Lower or Middle decide to sleep, the Middle will fold out to look like the first diagram. Once this happens, the Upper guy who was sitting on the Lower bench, has to climb up and stay there through the night. No window (so you never know which station you’re stopped at), and a (sometimes) annoying sounding fan right above your head.
The Lower also had the advantage of access to bags and food stuffed below the Lower bench. The Upper and Middle guys have to carry everything to bed with them once they all fold out.
Personally, I would always prefer Upper because I like to sleep in. Per etiquette, the Middle has to fold early in the morning so that Lower and/or Middle and/or Upper can sit and have chai and biscuits in the morning.
The best berth was the side-lower berth (explained below), which had a special configuration of only 2 levels, with the lower level getting 2 windows and the upper getting none.
In any given compartment, there were 2 sets of the diagram shown above facing each other (for a total of 6 people), and one set at 90 degrees with 2 levels (for 2 more people).
Upper
------------------ . | |
Middle []
------------------ . | |
[]Lower []
------------------ . | |
. = aisle
= windows
o = fan at ceiling level
| | = imagine this bench at 90 degrees to the benches on the left (cross-sectional diagram shown above), but with 2 levels instead of 3. The lower level of this set was always the best seat, because you could sit and get up any time you liked (the Upper in this case had to go up whenever you chose), and you got 2 windows.