Environment Transportation Zoobombing: Portland Phenomenon of Grown-Ups Speeding Downhill on Kiddie Bikes (Video) By Kimberley Mok Writer McGill University Cornell University Kimberley Mok is a former architect who covered architecture and the arts for Treehugger since 2007. our editorial process Twitter Twitter Kimberley Mok Updated November 27, 2019 CC BY 2.0. Gabriel Amadeus Share Twitter Pinterest Email Transportation Active Automotive Aviation Public Transportation Biking has generated a subculture unto itself, as seen with global naked bike rides, the decades-old Critical Mass and an endless parade of creatively customized vehicles. In Portland, Oregon -- long-known as a bike-loving locale -- a new form of wacky bike-riding called "zoobombing" has emerged, where adults ride customized kiddie bikes downhill at furious speeds. Taking place at an uphill spot during Sundays at 11 p.m., near the Oregon Zoo (hence the moniker "zoobombing"), the weekly gathering attracts an eclectic crowd ranging from pre-adolescents to middle-aged adults. The preferred vehicle is a bike with 12-inch wheels -- typically used by three-year-olds -- but many others choose 16 and 20-inch wheels, though the feeling of speed increases as the wheels get smaller. But it's not restricted to bikes; others have used skateboards, rollerblades and seated scooters --all sizes are welcome but most remains child-sized. Zoobomb has already marked its twelfth anniversary this year, despite some initial years of ambivalence from city officials regarding safety issues. But acceptance came about five years ago when the city unveiled a regional arts council-funded zoobombing sculpture that now doubles as parking for the group's kiddie bikes. The group's emphasis on strict safety protocol (which includes having a medic ride at the back of every ride) and open acceptance to people of all creeds has earned it a commendation from the city's police chief, who calls it a "great Portland institution." Gabriel Amadeus/CC BY 2.0 This urban sculpture is now nicknamed "The People’s Bike Library of Portland" or "The Pile." New riders are often lent a little bike from The Pile if they lack one. Says organizer and "bike librarian" of The Pile, Dave Terry, via Oddity Central, who estimates that over 10,000 people have zoobombed since 2002: We’re kind of the most badass thing you can be without having any discernible talent. It’s the original open source bike club. To our knowledge it’s the biggest bike club in the world. It’s open to anyone over 18 who is ready to have fun, be safe, be responsible and just have an unbelievable downhill bicycle ride that is rivalled by few, few places in the world. The group's approach to biking is fun and thrilling while keeping safety in mind, says Terry: There’s no routine, it’s absolutely chaos. You know, we don’t have a uniform like all the other bike clubs. The agenda is – grab bikes, go to the top of the biggest hill anywhere that we can find, and ride down at very appropriate speeds. It's another fascinating development in the evolution of bike culture that could potentially take root in other cities; for more info, check out Zoobomb.