Lisa Reed, Coleen Lonas and Stephanie Collins joke about the men in their lives on the Amtrak MARC train. The trio a others have formed a clique that occasionally drinks mimosas. (Daniel C. Britt/THE WASHINGTON POST)

Some days they make the 5:28 p.m. train. Other days, they have to wait for the 6:55. But sooner or later, Coleen Lonas, Stephanie Collins and a select group of commuters board MARC’s Camden Line at Union Station and take up their regular spot at the back of the second car.

By the time the train begins edging its way through Northeast Washington toward Maryland, the laughter and the beers are flowing as Lonas, Collins and the rest of their circle celebrate the end of another day.

Such gaggles are not uncommon on commuter rail lines like MARC. The trains’ predictable schedules make it more likely that riders will see the same faces each day, and the sometimes long distances the passengers travel give them ample opportunity to chat. Often, these conversations evolve into a kind of clique. Some, such as the one Lonas and Collins are part of, are organized enough to have their own Facebook group.

For the people who run MARC, the cliques add to the appeal of riding the rail line.

“We encourage it,” said Dave Johnson, MARC’s chief customer relations officer. “We have people that come from southern New Jersey all the way to D.C., so, of course, some will say hello to others. It just happens naturally.”

It’s difficult to measure exactly how many MARC passengers consider themselves part of such groups, but Johnson says the phenomenon occurs on all three of MARC’s lines, which serve 32,500 passengers each day. The Camden Line, which runs between Washington and Baltimore, carries about 4,500 of those.

Whether they started riding MARC a decade ago or just a few months back, Lonas, Collins, and most of their friends started out as solo travelers. But for extroverts such as them, perhaps the greatest thing about commuting by train is that you don’t have to be alone for long.

Today, they rarely are solo, with up to 12 at a time clustered around as many seats. Although some can only make it in the morning or the evening, Lonas and Collins and other core members tend to ride together both ways.

The recruiting of new members is informal. “One of these guys said ‘hello’ one morning, and it just kind of went from there,” said Lisa Reed, a financial officer at the Art Institute of Washington.

Some passengers try to wile their way in.

“They creep,” Collins said of such aspirants. “We call those people creepers, because they creep up the rows toward us. That’s what I did.”

“We don’t say no to anybody who wants to join us,” said Lonas, 58, an executive assistant at a lobbying firm and the Camden clique’s mother hen.

But this inclusiveness is not absolute, according to Collins.

“It depends on how mean you want to be,” Collins said. “If someone’s real annoying, we’ll just ignore them altogether.”

Frank Vallee, 49, who moved to Maryland from Boston last year to take a job with the Veterans Benefits Administration, was subjected to this selectivity as he made his move to join.

“I actually feel honored to be in this group,” Vallee said. “It was like hitting the lottery when we walked by these guys.”

Of course, not everyone seeks to join. Each group has its own character, and the Camden folks can be a little loud, especially after throwing back a few. Indeed, the freedom to consume alcohol sets MARC apart from other rail options in the region, and makes its clique culture a little more free-spirited.

“One group, they have a wine-tasting club,” MARC’s Johnson said.

Alcohol is not allowed on Virginia Railway Express, and all food and drink are banned on Metro. But on MARC, you can bring aboard whatever you like.

When Lonas and company launched into their own high-speed happy hour one recent evening, they brought a smorgasbord of Sbarro pizza, potato chips, Coors Light and chardonnay, all conveniently gathered within Union Station.

“It’s distracting; it makes it very hard to work,” said passenger Endymion Cooper, 28, a geneticist, after the bulk of the clique got off at the Dorsey station in Howard County. “I don’t know why I keep sitting here.”

Although Cooper seemed to prefer silence on the train to revelry, he sat well within creeping range of the Camden clique. With just one shared joke, someone such as Cooper could easily be pulled into the group.

“Some people hate us, but some people love us,” Collins said. “People have literally come up to us and said, ‘That was the funniest train ride of my life.’ ”

For the members of this group, the fun has spilled from the train into the rest of their lives.

“We were going to the bar a while ago and my husband said, ‘Are your train friends coming?’ ” Reed recalled. “I told him: ‘They’re not my train friends. They’re my friends.’ ”

When the train pulled into Union Station one recent morning, the group quickly dispersed onto the platform and beyond. Lonas stayed on the train as usual, waiting for the crowd to clear before disembarking. Eventually, she made her way to Metro’s Red Line and managed to find a seat. The train was packed, the fluorescent light harsh, and Lonas fell silent for the first time all morning.

Separated from her friends and nearing her office, Lonas gave up her cheery, matriarchal air for a more subdued, professional version of herself. But she perked up when asked which train she thought the clique might take home that night.

“I’m not sure yet,” she said. “But I can’t wait to find out.”