BTW, from reading this thread, it appears to me not everyone is on the same page as to "levels". (Most I think understand the differences but from reading it appears that some may not be.)
From what I understand, it comes down to the placement of the doors between cars, is it at the "standard" height of single-level cars, or at the higher height of the Superliner cars. This can make a big difference in how easy it is to get between cars on the train and as a result really makes a difference in functionality for folks.
With any of the bilevel/multi-level cars I'm available on the NEC, they're all have passageways to the next car at the standard height. This, among other things allows them to run in the same train as single-level cars without issue. HOWEVER, it means that while the door is at the level and some of the seats (and I think in all cases at least one vestibule), the majority of the seating requires you to go up or down. So to simply walk from one end of the car, you have to either go down, walk between some seats and go back up, or go up, walk between some seats, and then go back down. So if you want to move the length of say a 6 car train, you're going up and down 6 times. This is why a cafe car, or other car where passengers may want to move to is problematic for some passengers.
On the other hand, with Superliner, Surfliner/California Cars, they all have the passageway between cars at the upper-level. Once you're on the upper-level, you can go from car to car w/o having to ascend or descend any stairs what-so-ever. So, in theory, you can board at the lower-level and while still in the station and the train is not moving, ascend to the upper level, and stay there for the length of your trip. And in fact, I would say, especially for something like the Superliner configuration, I could easily see a Superliner III, incorporating a wheelchair left in say the cafe car, so that passengers could embark/disembark in one car, and have some freedom to move about the train (assuming they can navigate the narrowness). This simply isn't possible with the other form of bi/multi-levels since you'd need TWO in every car.
Like I say, I think most people in this thread realize the differences, but I was getting the feeling from reading some comments that some folks may not.
So I apologize for stating the obvious to anyone who already knew.
(oh so to put in my two cents, since you'll never likely have enough clearance on the NEC to have a car-type where you can have the passage strictly on the upper level and avoiding 2 sets of stairs in every car, it's unlikely you'll see any form of bilevel on the NEC).
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