"fixie" bikes - one speed (and no brakes!)

"In some of the toughest traffic in the country – New York, Atlanta, Chicago, Los Angeles – recreational bikers are stripping down their Schwinns and Cannondales and going back to the original setup that can be seen in pictures from the first Tour de France. Put another way, they're riding bikes torn from the velodrome and plunked down in the urban jungle... It is also rooted in a rebellion against the overaccessorized culture of spandex and 21-speed bikes of normal cycling... Yet, as with any edgy movement, a backlash is brewing. Some motorists question the sanity – and legality – of no-brake biking, while even a few professional riders, though impressed with the devotees' courage, worry about their astuteness. "These guys are adrenaline junkies," notes Atlanta track racer Leigh Foti. "They're going out there with no brakes!"

"Because it is possible to slow down or stop a fixed-gear bike by resisting the turning pedals, some riders think brakes are not strictly necessary. However, since the rider can apply braking force only to the rear wheel, the maximal deceleration is significantly lower than on a bike equipped with a front brake... A rider can also lock the rear wheel and skid to slow down or completely stop on a fixed-gear bicycle, a maneuver sometimes known as a skid stop... Other riders dismiss riding on roads without brakes as an unnecessary affectation, and that it is based on image rather than what is practical when riding a bicycle. Furthermore, riding brakeless may jeopardize the chances of a successful insurance claim in the event of an accident and, in some jurisdictions, is against the law..."

Text above from this article and from the Wikipedia entry. Image source here.