"I look forward to this every year," said McLaughlin, a multimode operator who's been with SEPTA for 15 years and has decorated cars for five. "It keeps my creativity going. On the bus, you're just driving all day - you're isolated. There's not much conversation. So this keeps you human. . . . You're not just a bus driver. This is like our break from the world."
McLaughlin didn't originate the SEPTA decorating tradition, which has been going on for at least 20 years and now includes seven cars and buses. But she has helped take it to a new level. Two years ago, she recruited her sister, a bus operator, to help out.
Both sisters, of Upper Darby, stopped decorating their homes for the holidays when their kids got older.
Now, they just go all-out on the public-transit cars.
The bus they decorated, to run on Route 38, included a mailbox for letters to the North Pole, a chimney with Santa emerging, and garlands laden with bells to jingle all the way from Fifth and Market to the Wissahickon Transportation Center.
The sisters wanted to add twinkle lights to the exterior of the bus, McLaughlin said, but they ran out of money. Supplies are saved from year to year, purchased by volunteers and SEPTA managers, or scavenged from the Santa Express, the train that runs every Black Friday, bringing Santa to his monthlong indenture at the Gallery mall.
The bus' wheels, fenders, and lug nuts, meanwhile, were getting a red-and-green paint job from Frank Toscani, a body mechanic, who said he was chosen for the job because he has the two requisite attributes of a good SEPTA elf: Avid attention to detail, and a deep appreciation for the trappings of the holiday season.
"If you go into any shop, I'm probably the only one that has the spirit," he said, gesturing toward speakers pumping out Christmas carols.
Toscani was allotted work hours to do the job, but said he'd finish on his own time if needed.
Come January, he'll have to return the flamboyant wheels and trim to the fleet's standard black-and-chrome treatment.
Back in the trolley barn, the sisters planned to give the windows a dusting of faux snow and wrap the trolley's signage like gifts.
After that, they'd start decorating a car running on the Norristown High Speed Line in a candy-cane motif.
Birton, a bus operator for 22 years, said her taste tends toward the conservative - pine garlands and dried cranberries - while McLaughlin opts for more sparkle and flash.
"We wind up putting it together, and we have a creation," Birton said.
Getting to collaborate with her sister is a nice Christmas bonus.
"Over the years we've been working here, we've become really close," she said.
Despite all that work, they don't usually get to drive the cars they decorate.
"Some of the drivers take credit for it and say, 'Yeah child, it took me all day to do this! And I did it all by myself.' We don't mind that they take the credit," McLaughlin said. "We know the real deal."
At the transportation center, though, everyone knows who's responsible.
"I get a lot of comments: 'Were you the one who decorated car 53? It looks great. And by the way, you got any tape? Because the garland's falling.' "
Really, though, it's not about recognition, Birton said.
"I like to do it because I know it's going to make someone happy," she said. "If someone's having a blah day, it's going to brighten up their day."
A week before Christmas Eve - with what the ad men would call seven shopping days till Christmas - a weary Hanifah Stevens, 44, broke into a smile as the Route 10 trolley approached, covered in loops of blinking twinkle lights that illuminated the dark subway tunnel.
"I wasn't in the Christmas spirit," the West Philly resident said, "and then this happened."
That holiday trolley - the handiwork of Gary Mason, a SEPTA operator who's been doing his own decorating for 20 years - was festooned with garlands, ornaments, bows, and even a miniature snow-covered village in front of the driver.
Insong Kim, 28, was one of several passengers to snap a photo of a shiny, plastic portrayal of a Santa of African descent; the piece holds a prominent place behind the driver.
Kim works as a sushi chef at Pod, so he's used to being surrounded by colorful, blinking lights - but he said he'd never seen a trolley like this.
"I was stressed out today, so it's a little relief."
SEPTA spokeswoman Heather Redfern said riders have started seeking out the decorated cars, which will be running through New Year's Day.
"We do get phone calls from people looking for the holiday trolley and when can they possibly catch it," she said. "We try to get the number of the vehicles and their schedule, but sometimes it's hit-or-miss."
Of course, the moment of surprise when passengers step off the platform and into a holiday party on wheels - that's what this tradition is all about.