As income levels in China increase, more people are driving cars, and China Environmental Protection Foundation hired DDB China to come up with a way to hammer into people’s heads that walking can be a better choice than driving. The result was beautiful — a public art campaign that had pedestrians “painting” leaves onto a tree with their feet as they crossed the street.

The company set up an “outdoor advertisement on the street” — a 41-foot-by-21-foot painting of a tree spread out across a pedestrian crossing. It was flanked on either side by sponge pads filled with washable, quick-dry paint. As people walked through the paint and onto the tree — sometimes on purpose, sometimes without realizing what was happening — their footprints created a green canopy on the once-bare branches.

These trees ended up being installed in 132 roads in 15 cities in China, where almost 4 million pedestrians participated. The idea was to make people feel the connection between walking and the environment more directly — it’s one thing to tell everyone that avoiding cars is good for trees, but a whole other thing to watch a forest blossom under your feet.