According to the New York Times, the New York City Metropolitan Transit Authority is considering, in the future, replacing the current subway trains with ones featuring "articulated train cars." These are in fact the opposite of what they sound like: instead of individuated cars making up a larger train, the train would become, essentially, one long train. New York wouldn't be a trendsetter: Cities like Shanghai and Paris have begun incorporating this kind of train.
There are clear benefits to this sort of train for a crowded city that's only getting more crowded, of course. Riders can be more easily distributed throughout the whole train, rather than bunching up uncomfortably in cars that happen to be near staircases and doors. It is the most scientifically efficient use of space. Fine.
But although I can think of some logistical snarls that single car trains might bring (wouldn't it be much worse, God forbid, if someone with a gun got loose on an articulated train?), mostly I think it'd break my heart a bit to see the subway change over to articulated trains. The subway car is the perfect miniature metaphor for living in New York. You are thrust into a small space with strangers, and sometimes that is just awful. Smells you can't escape, creeps with wandering hands, unstable people aggressively invading your personal space. That car also becomes a temporary community, though. It is something that feels finite and knowable in a city where the appeal lies in its infinite unknowability, but survival depends on finding friendly, smaller pockets. On a subway car, you share in the delight of an unexpectedly good dance troupe or share in the misery of an especially weird smell. On an uncrowded car especially, you can look around and imagine a life story for everyone sharing it with you. Or you can guess what they look like smiling, and who or what makes them grin. If the subway were one long car, sure, you could do that, but you'd also turn your head and a distant mass of faceless people would stretch in front of you, reminding you of the city's occasionally unfriendly vastness. Call me crazy (which, hey, would make me fit in on the subway!) but I think I'd rather put up with a crowded car than that feeling.