As with all great parties, I heard Friday night’s bike fiesta before I found it. Pedaling my old-school aluminum Trek road bike up one of Baltimore’s main drags — in a black bow tie, ruffled shirt, and cummerbund, naturally — I suddenly caught Whitney Houston’s “I Want to Know What Love Is” blasting from a nearby park. And then, up the hill a little further, I saw the 20-, 30-, and, yes, 40-something couples in retro tuxes, chiffon and satin gowns, with flowers in their lapels and corsages on their wrists, posing for pictures next to decorated bicycles.

There were even women with tiaras atop their helmets. One friend managed to dangle a sparkling disco ball off the front of her handlebars — lit by her bicycle light once we started riding and the sun went down. Close to 1,000 people in all. Not everyone, but most, dressed to the nines for that once-in-a-lifetime occasion.

Welcome to Bike Party: Bike Prom edition, part of a burgeoning movement nationwide that is putting the fun into bicycling activism.

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Last April, the traditional, anarchy-inspired Critical Mass rides here evolved (how long can something be both traditional and anarchist?) into the newer, safer, more traffic-friendly — and happier — last-Friday-of-every-month Baltimore Bike Party. Critical Mass rides, for the unfamiliar, date back two decades and have taken place in cities all over the world. They are historically political, punk, and confrontational in manner.

Bike Party, by contrast, is gentle, ’60s-style protest/celebration. It’s theater, activism, bicycling, and social gathering all at once. Or, as I overheard one woman tell a girlfriend on a ride: “It’s like everything I love rolled into one … and it’s going out on Friday night to a great party.”

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The rides are basically inclusive, 12-mile, recreational-speed cruises around Baltimore’s core downtown neighborhoods, including many neglected by the city and bypassed by other events. As a bonus, there’s always an awesome, eclectic soundtrack. Organizers launched a Kickstarter campaign earlier this year to pay for a kickin’ all-directional sound system that gets pulled along on a bike trailer in the middle of the action.

And, of course, there’s after-Bike-Party parties each month at a local bar. The monthly route gets shared with police, who occasionally help block traffic, but otherwise, it’s all very informal.

The Bike Party concept was apparently first launched in San José, Calif., where Baltimore organizer Tim Barnett, a Maryland Zoo zoologist by trade, says he got the idea to create a similar version in his adopted hometown.

Barnett, who was active in Baltimore’s Critical Mass rides, says he stumbled across San José Bike Party on the web while trying to find ways to attract more riders. He’d learned through social media outreach that Baltimore bicyclists wanted something more organized than the “leaderless” Critical Mass rides. And, he figured out, it needed to be fun — joyful even — if people were going to forego Friday night happy hour and participate.

“One thing people always said was, ‘I want to come [to the Critical Mass ride], but, you know, I’ve got this other thing to do,’” says Barnett, who doesn’t drive a car and says his motivation in organizing Bike Party is to help make bicycling a more acceptable, practical form of transportation in the city. “I wanted this ride to be the thing people did on their Friday nights.”

San José Bike Party volunteer Katie Heaney told the San José State University college newspaper that the group has been garnering more people each month since its formation in 2007. Many of the original riders of the group, she said, filtered through other bike party groups, such as Critical Mass in San Francisco and Midnite Ridazz in Los Angeles. On Facebook, the San José Bike Party now has nearly 14,000 “friends.” In March, they organized a Jedi-themed Star Wars ride, and late last year, attracted 3,500 riders to their fifth anniversary ride.

In 2011, San Francisco created its own popular Bike Party, followed by nearby East Bay and Peninsula Bike Parties in northern California. (There’s also Fresno Bike Party, Salinas Bike Party, etc.) Traverse City, Mich., and Philadelphia also recently gave birth to monthly Bike Party projects, as did Washington, D.C. A glance around the internet uncovered a Johnson City, Tenn., Bike Party, whose motto — “The Revolution Will Not be Motorized” — you gotta love. And, get this, there’s also Bike Party Seoul and Bike Party Changwon in South Korea, and Bike Party Sao Paulo in Brazil, too.

The Washington, D.C., Bike Party still has yet to capture the city’s imagination like Baltimore Bike Party has, perhaps unexpectedly to those who know the city only through The Wire. (The monthly rides in D.C., held since last July, attract about 400 riders a month.) But Baltimore Bike Party is merging bicycle commuters, recreational cyclists, and bike advoates, as well as the art and green communities, into a moving monthly parade that’s also moving city officials to pay attention to the burgeoning alternative transportation community here.

April’s ride, for example, was also associated with Baltimore Green Week, which hosted daily events in the week around Earth Day, including several bike rides. Next month, Barnett said, Bike Party will partner with the Station North Arts & Entertainment District on their May Final Fridays event. And in June, Mayor Stephanie Rawlings-Blake is expected to join Bike Party as it partners with the west side Bromo Tower Arts & Entertainment District.

The pure, mad joy of bicycling in costume with adventurous friends, literally filling a dozen blocks of Baltimore streets on a Friday night, is almost impossible to capture in words and photos. However, the absolute best part of any Baltimore Bike Party is the reaction along the route. More taxi, truck, delivery, and automobile drivers honk and toot in support than you’d think. But better are the diverse group of kids, teenagers, and adults in every neighborhood, east to west, north to south, who leave their rowhouses, come off their porches, step out of the corner bars and restaurants, stop whatever they’re doing to high-five Bike Party bicyclists, and shout encouragement — and often, shoot cellphone pictures and videos.

Young kids sprint and roller-skate on sidewalks to keep pace. Older kids jump on their BMX bikes and join in. Families wave from their windows. And some of these streets half-consist of boarded up, vacant houses. From one little boy with his sisters and mom during Bike Prom: “They wearin’ prom dresses! They’re SO beautiful.”

It’s also interesting to listen to Baltimore Bike Party riders themselves as they pedal. The bicycling culture in Charm City and the Bike Party — a year old — seems to be growing so fast now that it’s almost hard to grasp at times.

I actually heard another guy at a rest stop say, “I’ve been waiting for a bike ride like this my whole life.” He was probably in his mid-20s, but still.

I heard another cyclist ask, out loud, “How is it possible that this is the most fun thing I’ve ever done?”

I figure that sentiment has to bode well for the future of bicycling in Baltimore. Elsewhere, too.