http://gelardi.com/portfolio/contrail/
http://www.bikecontrail.com/
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.

The old cycle: More cars on the road more perceived danger for bikers fewer bikers on road even more cars on the road.

The new cycle: A few bicyclists ride with contrail a couple times per week faint lines on the road inspire curiosity and remind bikers where it's safe to ride new bikers are encouraged to ride and use contrail contrail lines get brighter as community grows.

By using this device, bicyclists will have a clearer path on which to ride safely and out of the way of vehicular traffic. At the same time, as more bicyclists using the Contrail go over a line created by a cyclist before them, the line gets brighter allowing drivers to clearly see a marked bike path where there might be none. It's sort of similar to what happens when a dirt path appears in a grassy field after lots of people have taken the same shortcut over a period of time.