When 23-year-old Patrick J. Stewart reviews a subway car for his subway-centric YouTube channel, he sometimes brings a white glove to stroke the poles, checking how besmirched his fingertips get. It is a good way to gauge how well a car is maintained, he says, and, by extension, how caring its overseers back at the rail depot are: The finger-swab is a health check on the entire system.

But a pristine car does not necessarily guarantee a good review. Subway cars, he believes, are supposed to be a little grimy. This is New York, after all.

“I love the subway system because of the fact that there is still some grit to it, some New York type of grit to it; there is still some of the old New York to be found,” said Mr. Stewart, a self-described subway fanatic and part of a posse called the Super Subway Bros., which over the past seven years has reviewed hundreds of trains and their lines in YouTube videos that cover every cranny of every car. “Everybody wants to come to New York City because of the fact that it’s New York City, not another city,” he said.

Rail fans are a phenomenon wherever there are locomotives, but the city’s subway system has its own ardent followers who study its maps and its tunnels, its history and its rail yards. The Super Subway Bros. are a group of young men, some from hard-luck backgrounds, who find an outlet for their obsession — and a measure of solace — in the labyrinthine train lines running stolidly beneath the streets. The members differ from many rail fans not just in their personal backgrounds (all of the Super Subway Bros. belong to racial minority groups), but in how they communicate their fandom: the internet. There, they supply a steady stream of videos, reviewing each subway line, critiquing car models or simply posting footage of trains coming and going. Though the footage might seem stultifying, it racks up views.