Dolly kept her mouth shut. She didn’t whimper or whine. She didn’t soil herself, either. So it was, I suppose, a successful trip by all accounts.

Dolly is a Maltipoo, a toy-sized mix of Maltese and miniature poodle. The pup is also a pioneer, of sorts, having ridden with her mistress, Shaunette Moore, on Amtrak’s Northeast Regional line from Washington’s Union Station to Newark, N.J.

On the way back to New Jersey, Dolly attracted celebrity-worthy attention.

“I’m so excited!” a woman exclaimed when she saw Dolly boarding with her pet carrier. “Can I bring my cats, too?”

Now, I have this theory that no matter how lovable a person’s pet may be to its owner, no one else wants to be bothered. (This is true of everyone except maybe hardcore pet lovers, but they’re usually the type who work at animal shelters enforcing regulations on pet adoptions as if they were handing over humans.)

But riding along part of the way Moore and Dolly, I don’t think anyone except Shaunette knew the dog was there. The only sign that she had a living creature aboard was that the mesh carriage seemed to be breathing. The truth is, people’s early morning train station breakfasts – who eats a hotdog at that hour? – were more nauseating.

Since Amtrak expanded its “Pets on Trains” program, the only complaints I heard during a couple trips with pets aboard were mild ones, and those were from conductors who declined to give their names because of the railroad’s policies forbidding them to comment.

So I’ll keep my yap shut for now. But I wonder how this is going to work when someone’s beloved Fifi brings a taste of all the fun and frolic of a dog park inside a fully booked train car.

Amtrak expanded its “Pets on Trains” program in October to the East Coast, just in time for holiday bedlam. The program built on a successful pilot program in Illinois.

Amtrak announced this month that Pets on Trains is going national. The program will be in effect on trips up to 7 hours beginning Feb. 16. A  weekend-only pilot program on Acela Express is starting on Feb. 20.

More than 2,700 pets have traveled on the Northeast Corridor since the program was expanded there in October, the railroad said.

The idea was first tested in the Midwest and has spread since. Amtrak spokeswoman Chelsea Kopta said more than 200 animals traveled on the railroad’s inaugural pilot in Illinois, and there were no complaints. Not one. And no incidents, either. Amtrak officials say the program came in response to passengers who wanted to travel with pets. The federally subsidized (and money-losing) railroad also hopes the program will boost ridership and revenue.

Pet owners have to register. They are permitted to take a small cat or dog in an enclosed carrier. Maine Coons and Great Danes are out, unless those breeds of cats and dogs can somehow conform to the requirement that animal and carrier weigh no more than 20 pounds. The carrier also has to fit under its owner’s seat.

Animals must be at least eight weeks old and they have to have current vaccination records. Owners must arrive at the station 30 minutes before boarding to check in and sign a waiver form. The cost is $25 for a pet’s one-way trip. For Moore, that meant laying out $200 on fare for her and her pooch.

Moore said traveling with her dog was a bit of a hassle, at least until she could take a seat. That’s because she was also schlepping a purse and luggage. Getting up the train’s stairs from the platform was a pain. The trip to Washington, she said, was cramped but otherwise fine.

“We had to, like, squeeze in. They don’t want them to come out of the cage. But, eventually, she started crying,” Moore said. “She gave a couple barks, but she calmed down.”

“I try not to even see them,” said one conductor when asked what he thought of dogs riding in his carriage. “I don’t really think they thought it through.” Already he said he’s seen pet owners remove them from the carrier and put their animals on the seats. He’s had to tell them to put them back in the carriers.

During other recent trips, neither of two conductors working the train was aware that pets were aboard. One of them was Baxter, a Jack Russell terrier who belongs to William Hartmann.

Hartmann, 23, of Germantown, said this was his second run with Baxter, who seemed amazingly sedate for a Jack Russell terrier.

“I mean, I gave him a half a Benadryl, and that helps calm him down a bit,” Hartmann said, referring to the antihistamine that can act as a mild sedative. “But, no, I’ve never had a person complain.”

Hartmann was on his way to New Jersey for Christmas. He also had traveled with Baxter during the Thanksgiving holiday. His only hassle came from a conductor who told him the carrier was too large. But fellow passengers rose to his defense. He’s also seen a cat riding the rails, and also without much trouble.

“I love it. Being able to commute to my family and take my pet is perfect. I’d feel horrible leaving him at home with a sitter,” Hartmann said.

Leslie G. Lewis is no stranger to taking her pooch on the train. Before Amtrak’s program began, she said, she sometimes smuggled her dog aboard, a tiny cocoa-and-white Pomeranian named Mia who even has her own Instagram feed (miathepom, for those asking).

Mia was under the weather: it was thought that she picked up a bug from other dogs at a celebrity-themed holiday dog party in Brooklyn, despite being attired in her nattiest Christmas sweater. (The hostess was one Chloe Kardoggian.)

“It’s easy to travel with her,” said Lewis, 30, who lives in dog-crazy Alexandria, Va. and teaches yoga.

Sitting on the floor of Penn Station before taking a red-eye back home, Mia panted nervously inside her carrier. Lewis had unzipped the flaps to give her some air. When it came time to board, Lewis stowed the carrier under her seat. As the train rumbled along, now and then her dog emitted a hoarse, chuff, chuff, chuff. It was audible, but just barely. The squeaky baggage shelf overhead was louder.

“Normally, you wouldn’t even know she was here,” Lewis said. “But I had a friend who had a nasty little Chihuahua that would bark. They threatened to throw her off the train.”