http://www.besportier.com/archives/chalk-bike---contrail-biking-community-tool.html

Riding a Chalk Bike with a Contrail is a cool way to develop bicycle communities. To make your bike a Chalk Bike, simply attach the Contrail Biking Community Tool to the wheels of your bike. The Contrail then applies a thin layer of colored chalk to a bike's tire, and as you ride, it leaves a faint chalk line behind your bike. This concept was created by Studio Gelardi which states, "The goal is to encourage a new cycle of biking participation by allowing the biking community to leave a unique mark on the road and to reclaim this crucial shared space." This will work towards reminding car drivers of the ever mounting presence bikers have on the road. Very cool, and we hope to see this playful artwork on the street soon!