To some, it's a party on wheels. To others, it's a rolling protest. To many, it's just a recreational ride; a nice, safe way for bicyclists to get together. But for their car-driving counterparts, the monthly ritual is little more than an intentional traffic jam.
Whatever you want to call it, Critical Mass attracts dozens of cyclists who take to the streets of Boston - and about 300 other cities - on the last Friday night of every month.
Brian Duffy, who has been commuting to work by bicycle every day for more than 20 years "in rain or shine," was one of the first to arrive at Copley Square for the late-December ride. He brought his 17-year-old son for an introduction to the "CM" experience.
"He tells lots of stories about Critical Mass. It's all he talks about," Griffin Duffy said of his dad. "He even has the hat," he said, pointing to his 50-year-old father's helmet cover, a bright yellow blowfish skin with fins, googly eyes, and 10-inch Lycra spikes.
Critical Mass originated in San Francisco in 1992 when a group, originally called the Commute Clot, distributed fliers before a ride. Though it's a loosely organized group and members fiercely resist being identified as activists, they promote alternatives to automobiles and try to increase awareness of bicyclists' needs.
The group appeared in Boston during the summer of 1999. A leaflet touted "bicycles riding together in joy and solidarity and stuff, changing the world and all." It continued: "But you don't even have to think about that. It's just lotsa fun."
Though participants say it's not their intention to disrupt traffic, they try to assemble as large a group as possible to attract attention and boost the camaraderie. The result, whatever the intention, is a traveling traffic jam.
About 30 riders left Copley Square shortly after 5:30 p.m. on Dec. 28, riding five abreast, and proceeded to cut up and down the streets of Chinatown and downtown. When they approached intersections with traffic lights, one cyclist swooped to the side, jutted out an open palm and stared down a driver, allowing the rest of the group to safely coast through in a tactic known as "corking," "plugging," or just blocking traffic.
Police say this maneuver isn't legal, but nobody gets arrested unless police see them in the act.
"We always get calls about them," said Officer Frank Pasquarello, spokesman for the Cambridge Police Department. "If there's a violation, we will stop them. . . . At red lights they have to stop. On some occasions, we have had a talk with them. But we have no problem with them if they obey the laws."
Critical Mass has caused contention in many communities - from New York, where hundreds of massers were arrested at the 2004 Republican National Convention, to San Francisco, where Mayor Willie Brown declared war on the group. The group's activities have spawned the term "U-lock justice," which describes revenge taken on an overly aggressive car by means of a metal bike lock.
Several participants have disassociated themselves with CM members who step over the line.
"There is a classic group called the testosterone brigade," said Adam Kessell, who helped organize the Boston group and created its website. "The more aggressive bicyclists that are not friendly to the car drivers, or other riders, kind of get pushed out because they don't understand what we're trying to do."
Still, Kessell isn't advocating diplomacy. Instead, he said, CM allows participants to assert their rights to the road through civil disobedience.
"Stop and wait at a red light and get better treatment?" Kessell pondered. "There is no evidence that that works. . . . There is a position that bicyclists should behave exactly like drivers and follow all the rules of the road. If you look at the history of societal change, that's counter historical. Now conditions are much better in terms of bike racks, lanes, rules, and laws that are favorable to bicyclists."
For Lindsey Barcebal, a Boston College senior who memorialized a fellow bicyclist in August by painting and placing a "ghost bike" in the South End, the monthly ride serves a positive purpose - even though she has seen violent retaliation, as when her friend was punched in the face by a disgruntled driver during the ride in May.
"A lot of cars just aren't aware of bikes in the streets, and there are accidents," said Barcebal, sporting a yellow reflective jacket while riding with the group. "This is to show cars we have every right to take the road, even in the winter. There are a lot of fair-weathered bicyclists out there that need to be shown we can do this."
As the group crossed the Longfellow Bridge, taking up two lanes of traffic, they set off a crescendoing chorus of car horns. Logan Wangsgard, 26, of East Cambridge, simply turned his head toward the cars, smiling and waving.
Under a pitch-dark sky, the cavalcade stopped at about 6:30 before the colonnade of the main building at the Massachusetts Institute of Technology.
The riders filed in, one by one, with their bike frames hung from their shoulders, then remounted once inside and biked through the building.
"This is the first time we've done this," Wangsgard said, rolling by bulletin boards, classrooms, and students. "I'm surprised there aren't more confused-looking people here."
After returning to Boston via the Mass. Ave. bridge, the group had dwindled to about 10 at 7 p.m. One rider blocked a whole lane of traffic, sending the woman in the van behind him into a frenzy of honking and hand gesturing.
Farther up, the drivers who were able to blow past the group let off their horns. The driver of a PT Cruiser slowed by the side of the group, rolled down the window, and let out a litany of obscenities.
"I gave his car a little love tap," one cyclist said afterward.
"I spit on him," said another.
His friends let out a laugh and kept pedaling into the night.