Every night, while they try to sleep, thousands of vehicles zip along just above their hidden home, showering them with road spray, an occasional piece of trash, and the dissonant melodies of squealing tires and groaning engines.
As the temperature plunged below zero and the snow piled up, it has become even harder for Jesus and Tanya Rodriguez to eke out an existence beneath the twin spires of the Zakim Bridge.
``We pay attention to the weather very closely,'' said Jesus Rodriguez, 29, who has lived in his secret spot since the fall with his wife, her younger brother, and their friend. ``We're trying not to take any chances.''
The group members, living on a wooded perch within the maze of overhead and surrounding roads, are among dozens of people in the city who persist in living outdoors, putting themselves at great risk, city officials say.
``We're really concerned about those people who feel they can stay out now because they have stayed warm so far this winter,'' said Jim Greene, commissioner of the city's Emergency Shelter Commission. ``The difference between 20 degrees above zero and below zero can be life and death. The layers that protected you at 20 degrees above aren't going to cut it at 20 degrees below.''
In the city's annual homeless census in early December, when the weather was still comparatively balmy, officials counted 182 people living outside. More recently, they estimate there are fewer than 40 people living on the streets regularly, but that number doesn't include those in the Rodriguezes' encampment, which, like others, was designed to elude authorities.
Officials who oversee the city's homeless shelters say it has become even more of a challenge in recent months to persuade some homeless people to come inside. The closing in October of the Boston Night Center, which allowed those barred from other refuges to stay the night, has made other shelters more crowded.
Beth Grand L'Heureux, co-director of the homeless service bureau of the Boston Public Health Commission, said that in the past couple of weeks there have been 33 more people staying in the city's largest shelters every night and 508 more beds filled than in the same period last year - due in part to the weather and the closing of the Night Center.
The Rodriguezes said they often slept at the Night Center because it was the only shelter where they could sleep together, even if on a floor.
Since it closed, they, like others who used to stay there, have preferred to live outside rather than go to other shelters, where they and their friends say they have been robbed, attacked, or gotten sick. But they said they would much prefer to live in their own apartment and hope to get subsidized housing soon.
``I would say if you're not homeless, don't go here,'' said Tanya Rodriguez, who said she started living on the streets three years ago after graduating from high school in West Bridgewater. ``It's not easy doing this every night.''
The couple, who had to replace one tent that collapsed, said they married six months ago and have since been joined by her brother Shawn Cagnina, 18, and a friend, Anthony Auger, 21.
As the weather has grown more blustery, they relied on each other and found ways to survive. They have received tents, air mattresses, jackets, socks, blankets, and other necessities from groups and people in the city. They share granola bars, bottled drinks, and other food. They use money from panhandling to buy hand and foot warmers.
But as temperatures plunged, it has become impossible for Cagnina to sleep through the night. ``It's just too cold,'' he said, adding that they spent the weekend staying with friends.
``The hardest part is when the snow collapses my tent,'' Cagnina said, adding that he has had money and shoes stolen at shelters. ``This isn't ideal, but it's better here - when it's not so cold.''
For Auger - homeless for two years since his family's house burned down in Braintree, his mother was killed shortly after, and his father moved out of the country - surviving such cold temperatures means taking the right precautions.
He sleeps inside three sleeping bags with additional blankets covering his head, and with multiple hand warmers. ``As long as it's not overly harsh winds and subzero temperatures, I think I'm good,'' he said.
The harder part is figuring out how to get out of what he recognizes is a bad situation. Inside a garbage bag in his tent, he keeps a tie, blazer, collared shirts, and dress shoes, which he uses to apply for jobs.
``I'm just frustrated with being homeless for so long,'' said Auger, who hopes to enroll in college. ``I feel stuck and out of control. It's bad, and I'm ready for things to change.''
David Abel can be reached at email@example.com. Follow him on Twitter @davabel.