Like ants leaving a scent trail for other ants to follow, cyclists can follow the trail of other cyclists with the Contrail Biking Community Tool designed by Pepin Gelardi and Teresa Herrmann for a competition.
A doodad deposits chalk powder on the rear tire, which in turn leaves a trail of chalk on the road showing the bicycle’s path on the road.
As more cyclists ride along the chalk marked route, the routes become more visible to cyclists and motorists, just like ant trails are reinforced as more ants use the path.
I really like this, though I hope I’m not directly behind a cyclist using one of these — it could be pretty bad for the asthma. Doobybrain describes this concept as useful for showing cyclists where to “ride safely and out of the way of vehicular traffic,” but the illustration above accurately portrays that the safest place can be in the lane with vehicular traffic if lane width warrants it. Gutter bunnies are dead bunnies.