The Contrail is a conceptual bicycle device that would allow bicyclists to leave a trail of chalk where they ride, to create de facto bike paths with unique marks on the road and thus, in the words of its creator Pepin Gelardi, "reclaim this crucial shared space." Click here to check out the concept drawings, then weigh in:
Interesting idea -- get that thing into production pronto!
Kinda useless -- let's just begin with two words: "rainy day"
Love it -- The Contrail is a marvel of chalk engineering!