I see it all the time on off-peak trains. The rear coach (sometimes two) is closed off to passengers. When I ask the conductors about the closed car, the response ranges from "not enough people/staff," "manifest such-and-such," "broken but maintenance may let us open it down the line." Really, all these excuses ring a bit hollow. My guess is that the real answer is, "We don't want to open it unless the train gets uncomfortably full since it means less walking for us, and we can use it as our private, non-rev car. After all, one ticket entitles you to one seat, and there are plenty of (single) seats."

So, who makes the call on how many cars in the consist are opened? Do the operations folks centrally decide for each train based on loads? Do the conductors decide on their own? Is there pressure from upper management not to open more cars than necessary to save on cleaning?

While I have no problem with this practice during bona fide light loads, I really think that the every coach should be utilized once the train runs out of seat-pairs. I've seen fairly full trains with the rear coach closed. Letting people spread out is a welcome courtesy, and the incremental cost of cleaning can't be that much higher, especially if the labor for cleaning is a fixed cost.