Bike 'Contrails' to Create DIY Bike Routes

Contrail is a tool for developing bicycle communities. As you ride, contrail leaves a faint chalk line behind your bike. 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.

http://www.treehugger.com/files/2009/03/bike-contrails-diy-bicycle-path-chalk-design-concept.php