a huge balloon, tied to a car�s vent-pipe, depicting the amount of exhaust emissions a car releases a day.
the "bursting earth" project is similar, but more dynamic. activists attach world globe balloons on exhaust pipes of cars in Berlin. the exhaust gas inflates the ballons. after the message becomes readable, there is a big "bang".
[link: frederiksamuel.com & adsoftheworld.com & 20to20.org]