On Nov. 14, a crosswalk appeared at Seattle’s busy intersection of Olive Way and Harvard Avenue. The city’s department of transportation was not happy about it.

This new crosswalk was unauthorized; a group of residents of the city’s Capitol Hill neighborhood painted it themselves. Two days later, Seattle Department of Transportation workers were at the scene, power-washing the zebra stripes into oblivion…

Such acts of unsanctioned “tactical urbanism” are of a kin to many other DIY street interventions, such as pop-up bike lanes. But they are not without risks. Affluent communities could have more residents willing to volunteer time and resources, for example, even though pedestrian deaths are concentrated in low-income neighborhoods.